Module 1 The Nervous System

Unit Intro

Unit 1 - Nervous and Endocrine Systems

In This Module

Introduction

Module 1: The Nervous System Aids in Maintenance of the Status Quo

In this module you will explore both the conscious and unconscious communication of your body. You will do this through an examination of the structure, organization, and function of the nervous system. You will discover how the nervous system works to maintain homeostasis, and you will learn what occurs when communications are disrupted or interrupted. You will research how imbalances and disorders cause the nervous system to function improperly and how medical technologies can be applied to correct these situations.

As you progress through the course, you will be encouraged to use science and technology to acquire new knowledge and to solve problems. The scope and characteristics of science, its connections to technology, and the social context in which it is developed will be examined. You will be asked to critically address science-related societal, economic, ethical, and environmental issues.

Throughout this course you will find references to “The Key.” This is a Castle Rock Publication available for purchase from the Distance Learning Resources Branch, and from local book stores. This reference for Biology 30 includes multiple choice, numerical response and written response questions from past Diploma exams. You will find this a useful resource for review and studying. In addition to providing sample questions, an explanation of the marking rubrics used to grade the Diploma exam is also provided. It is an invaluable resource available to students preparing for the Diploma exam.

In This Module

Lesson 1: Structure and Organization of the Nervous System

When you were attracted to the new person in the room, you couldn’t control your breathing rate or your heart rate.  You withdrew your hand without thinking about it. The only thing you seemed to be able to control was walking across the room. But what would happen if you couldn’t even control the muscles moving your skeleton? Can technology help your body communicate with its’ various parts?

In this lesson you will investigate the following focusing questions:

• How is the nervous system organized and how do these parts communicate with each other?
• What interrupts the normal communication mechanisms of the sympathetic and parasympathetic parts of the nervous system?

Lesson 2:  The Brain and Spinal Cord—The Boss and Unthinking Boss

All information about your internal and external environment is transmitted to the brain and/or the spinal cord. The brain is the control centre for your body, just like the nucleus controls cell function. But if the spinal cord is damaged, then your brain can’t communicate successfully with your body. What are the implications? 

In this lesson you will investigate the following focusing questions:

• What are the main structures of the brain and spinal cord, what are their functions, and how do they coordinate those functions?
• What happens when the information to or from the brain or spinal cord is disrupted or interrupted?

Lesson 3:  The Basic Units of the Nervous System—The Neuron and the Reflex Arc

How embarrassing! You yanked your hand away from the very person you wanted to meet. How did something like that happen? You certainly didn’t plan it that way! Could this be like burning yourself on a hot stove? Why is your reaction so fast? Why do you become aware that the stove was hot only after you have moved your hand away from the source of heat?

This lesson helps you to understand the following focusing questions:

• What are the structures and functions of the neuron, and how do they support communication?
• What are the components of a reflex arc?

Lesson 4:  Sensory Perception—Taste, Smell, Touch, and Temperature Sensations

In the group of people that you approached, perhaps someone was eating pizza.  You could just taste it, even if all you could really do was smell it. Then there was the pain of the handshake, and you felt the room heat up. Or were you just embarrassed and getting hot and flustered? The nervous system responds to environmental stimuli. It does this through the senses.

The following focusing question will be addressed:

• What information about our environment do the sensations of touch, smell, and taste communicate to our nervous system in order to maintain homeostasis?

Lesson 5:  Photoreception—The Eye

Vision is our dominant sense. Do you wear contact lenses or glasses to help you see? If so, which parts of your eyes are not functioning well? Do we all see the same things?

The following focusing question will help you to understand the concept of photoreception:

• What are the major parts of the eye, how do they function and how do they communicate with the nervous system to support the integrated act of seeing?

Lesson 6:  Mechanoreception—The Ear

Your phone is ringing, but you can’t find it. No point asking your parents because they can’t hear it. Do we all hear the same things? Do other people in the room notice the laughter? Your heart starts to beat faster and you are breathing faster. Maybe you remember a time when this happened to you and you get dizzy. The ear also plays a role in establishing balance.

Understanding the following focusing questions will help you to learn about mechanoreception:

• What are the sturctures of the ear and what are their functions in communicating sound?

• How does the ear impact your ability to maintain balance within your changing environment?

Lesson 7: The Nerve Impulse—Transporting the Message

When you see the rotating dancer or you hear the mosquito ringtone, how are the image from the retina of the eye and the sound vibrations from the Organ of Corti communicated to the brain? Sometimes the messages are disrupted by disorders such as multiple sclerosis. What happens when communication is interrupted?

You will investigate the following question:

• How does the structure of a neuron facilitate the reception and transmission of a nerve impulse to the synaptic gap?

Lesson 8:  Synaptic and Neuromuscular Transmission—Crossing the Divide

Neurons are physically separated from each other by tiny gaps. The nerve impulse must be transmitted across this gap by chemicals called neurotransmitters. What might compromise synaptic transmission? Why does coffee excite your nervous system whereas alcohol inhibits it? How do anesthetics work so that you do not feel pain during surgery? Michael J. Fox and Mohammed Ali both have Parkinson’s disorder. How does this disorder interrupt synaptic communication?

To understand the concept of synaptic transmission you will investigate the following focusing questions:

• How do the anatomy and function of the synaptic gap and neuromuscular junction facilitate the transmission of nerve impulses between neurons, and between neurons and effectors?

• How do chemicals that we take into our body and disorders such as Parkinson’s Disease compromise synaptic transmission?

Big Picture

Big Picture

You are at a gathering with your friends and a person across the room catches your eye. You notice their smile and can hear their laugh from across the room. You decide you want to communicate with this person, so you walk across the room to say “ hi”. You notice that you’re breathing faster, your heart is pounding, and your hands are clammy. You are introduced and you shake hands. Without thinking, you yank your hand away from the handshake that’s hurting your sprained finger. You’re so embarrassed! Your body is communicating even if you didn’t want it to! You stammer out a hello and they say hello back. You can see from their body language that they are nervous as well. Whether you end up with a friend, or someone who rejected your attempts at communication will ultimately be up to you.

While you may have felt like your nervous system was not working correctly because you could not control what your body was communicating, it was in fact responding and working to regain homeostasis. You take a deep breathe and the unconscious parts of your nervous system bring your heart rate back to normal.

In this Module you will learn about the many ways your Nervous System communicates with your body to speed you up, slow you down, and establish homeostasis.
 
In this module, you will explore how the body communicates through the nervous system? 

To do this, you will need to explore the following focusing questions:

• How is the nervous system organized? How do its parts communicate with one another? What could interrupt this communication?

• What are the main structures and functions of the brain? How does the brain establish communication? What happens when this communication it is interrupted?

• What are the main features of the spinal cord? What role does the spinal cord play in the communication and coordination of the rest of the body?

• What are the features of the building blocks of the nervous system?

• What information about our environment do the sensations of touch, smell and taste communicate to our nervous system in order to maintain homeostasis?

• What are the major parts of the eye? How do they function? How do they support the integrated act of seeing?

• What are the major parts of the ear that facilitate your response to sound and facilitate your ability to maintain balance within the changing environment?

• How does the structure of a neuron facilitate the reception and transmission of a nerve impulse to the synaptic gap?

• What are the events in the synaptic gap that affect how neurons communicate with each other?

Lesson 1.1.1

Lesson 1—The Structure and Organization of the Nervous System

Get Focused

Remember from the Big Picture when you were in a room full of people and you hoped to meet a new friend? You started to breathe fast and your heart rate went up as you made your approach. It took an effort to calm yourself down. In this situation, you could not control your breathing rate and your heart rate, but you did have control of your legs.

Can you imagine being able to control your breathing and heart rates like you control your legs? This is where the nervous system gets divided into the unconscious or involuntary sections and the conscious or voluntary parts. Processes vital to life, like breathing, are controlled unconsciously. Just try to see how long you can hold your breath. In this lesson you will explore mechanisms that increase your breathing rate and slow it down, returning you to a normal or balanced state. This state is termed homeostasis.

Controlling your skeletal muscles, such as your legs, is a conscious or voluntary act. In Lesson 1 you will discover the part of the nervous system responsible for voluntary control and what happens when these pathways are interrupted.

Injuries, such as paralysis or the loss of a limb, can interrupt communication in the conscious nervous system. In the case of someone recovering from a car accident, this person may learn how to walk again through the re-establishment of conscious nervous system communications. This may be achieved through physiotherapy, surgery, and other technologies developed to enhance or repair communication pathways.

In this lesson you will investigate the following focusing questions:

• How is the nervous system organized, and how do these parts communicate with each other?

• What interrupts the normal communication mechanisms of the sympathetic and parasympathetic parts of the nervous system?

While you are working through Lesson 1, you will start working on the module assessment.

Module 1: Lesson 1 Assignments

 Once you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio 30 1.1.1 online assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut# 1.1.1

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Explore

Watch and Listen

View the BiologiX 1 video “Electrochemical Control Systems in Humans:Regulating Physiological Process.”

This video presents the two divisions of the nervous system. These are the central nervous system, composed of the brain and the spinal cord, and the peripheral nervous system. Watch for the divisions of the peripheral system and how they control the body consciously and unconsciously. This video demonstrates communication and homeostasis. The video also explains the structures of the neuron, which is a basic building block of the nervous system, and outlines how neurons aid communication.

“Electrochemical Control Systems in Humans: Regulating Physiological Process” also examines the organization of nerves and shows how nerves network to support communication. As you explore typical communication, keep in mind what could result when interruptions occur in, for example, multiple sclerosis and Alzheimer’s disease.

Read

The video provides a good foundation on the various parts of the nervous system and how they work. You may wish to read pages 366 to 369 in your textbook and make summary notes for your course folder to increase your understanding of the nervous system.

Try This

TR. In both the video and the reading, the divisions of the nervous system including the autonomic nervous system and the somatic nervous system were presented as being vital towards maintaining homeostasis.

This is your opportunity to practice your understanding of the autonomic and somatic nervous systems and how they communicate to maintain balance.

You can revisit the video or the reading if you need to review these systems.

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Self-Check

SC 1. Complete this Self-Check activity which compares the autonomic nervous system with the somatic nervous system.

Self-Check

Test yourself to see whether you have learned the concepts in this lesson.

SC 1. Define homeostasis. Illustrate your answer by using body temperature as your example.

SC 2. Explain why the nervous system is critical for maintaining homeostasis.

SC 3. Identify what basic neural pathway is involved as you dodge a misdirected tennis ball.

SC 4. How is the autonomic nervous system different from the somatic nervous system?

SC 5. Why do you have to learn how to walk but not how to breathe?

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Lesson Summary

In this lesson you investigated the following focusing questions:

• How is the nervous system organized and how do these parts communicate with each other?

• What interrupts the normal communication mechanisms of the sympathetic and parasympathetic parts of the nervous system?

To answer these questions, you explored the human nervous system as a complex communication system organized into the central nervous system and the peripheral nervous system. These systems work together to maintain homeostasis.

The motor neurons of the peripheral nervous system take information from the brain and spinal cord to the somatic nervous system and/or the autonomic nervous system. The autonomic nervous system is composed of two subdivisions (parasympathetic and sympathetic systems).

The functional unit of the nervous system is the neuron. Neurons bundle together to form nerves. The nervous system gathers information using sensory neurons or a sensory pathway. And the nervous system integrates information using interneurons like those found in the brain and spinal cord. Instructions are then transmitted by motor neurons or motor pathways to muscles and glands. These muscles and glands are called effectors because they initiate a response.

Lesson Glossary

autonomic nervous system (ANS): a division of the peripheral nervous system that conducts nerve impulses to cardiac and smooth muscles, as well as to glands; may also be called the involuntary motor system

central nervous system (CNS): the part of the nervous system that includes the brain and spinal cord

homeostasis: a state of body equilibrium or a stable internal environment of the body

nerve: message pathway of the nervous system; made up of many neurons grouped into bundles and surrounded by protective tissue; there are 12 pairs of cranial nerves that insert into the brain and 31 pairs of spinal nerves that emanate from the spinal cord
nervous system: an elaborate communication system that receives input, processes, integrates, stores information, and triggers muscle contraction or glandular secretion

neuron: the basic functional cell of the nervous system that is specialized to generate and transmit nerve impulses (messages)

parasympathetic nervous system: division of the autonomic nervous system that oversees digestion, elimination and glandular function; often works opposite the sympathetic nervous system to bring the body back to normal
peripheral nervous system (PNS): the portion of the nervous system consisting of nerves and ganglia (collections of nerve cell bodies) that are outside the brain and spinal cord
somatic nervous system (SNS): a division of the peripheral nervous system that conducts nerve messages to the skeletal muscles; may sometimes be called the voluntary nervous system
sympathetic nervous system: division of the autonomic nervous system that activates the body to cope with some stressor, such as danger, excitement, or fear; sometimes referred to as the fight, fright, flight subdivision

Lesson 1.1.2

Lesson 2—The Brain and Spinal Cord: The Boss and the Unthinking Boss

Get Focused

Everyone has a brain and a spinal cord. Most people are born with both working the way they should. The brain is the centre of “who” you are—your personality, your values, and your ability to determine right from wrong. Your brain communicates with your spinal cord allowing you to walk, move, feel, experience life, and perform body functions like breathing.

When you walked across the room to meet your new friend in the Big Picture, it was your brain that projected your personality and your spinal cord that got you there.

In this lesson you will explore the relationships between the brain and the spinal cord and how dependant they are on each other to function correctly. When the communication is interrupted between the two, bad things happen. For example, your personality could change, you might lose the ability to walk, or your senses could be altered. Each of these is an example of interrupted communication.

In this lesson you will investigate the following focusing questions:

• What are the main structures of the brain and spinal cord, what are their functions, and how are these functions co-ordinated?
• What happens when the information to or from the brain or spinal cord is disrupted or interrupted?

Module 1: Lesson 2 Assignment

Once you have finished all of the learning activities for this lesson, you can complete the online assignment.

Bio30 1.1.2 online assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#1.1.2 CNS

1.1.2 page 2

Explore

Read

The brain is the control centre of your body. To understand where the brain processes the sight of a friendly face across the room or the laughter you heard which motivated you to cross the room, and controlled your breathing and heart rate, read pages 386 to 395 of your textbook. Make summary notes for future study, and place these notes in your course folder.

Watch and Listen

The following videos will provide an excellent introduction to the concepts that will be presented in this lesson. You may wish to return to these videos as you complete future lessons.

Introduction to nervous system video

Brain Parts and Functions

 Self-Check

SC 1. After reading the text and viewing the video, you will have come to know that the occipital lobe processes sight and the temporal lobe processes the sounds. There are, however, four major lobes of the brain. This diagram provides information on the functions of all four lobes. Consider this information as you identify and label the name for each lobe.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 390, fig 11.29. Reproduced by permission.

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Read

You must know the structure of the spinal cord to understand how it performs its role in the nervous system. Read pages 385 and 386 in your textbook. Make brief summary notes for your course folder.

The spinal cord is a major communication link between the brain and the peripheral nervous system (PNS). As you learned in your reading and in the video, the spinal cord is protected by the backbone and cerebrospinal fluid. You will learn about the role of protection to the nervous system and other functions of this fluid later in this lesson.

The spinal cord is made up of two special types of nerves. Sensory nerves communicate messages from the body to the brain for interpretation, and motor nerves communicate messages from the brain to effectors that initiate a response. In Lesson 3, you will learn about these communication pathways, and you will discover another communication role of the spinal cord, the reflex arc.

Self-Check

SC 2. After you have read the text and made your summary notes, complete the handout titled “The Spinal Cord.” To prepare for the next lesson, you may wish to include with the name of each structure in the diagram a statement about the structure’s composition. For example, a spinal nerve is composed of both sensory and motor neurons. Self-check your answers, and file your work in course folder.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 386, fig. 11.23. Reproduced by permission. 

The Meninges and Cerebrospinal Fluid

Try This

As you know from your lesson reading, the brain and spinal cord are essential structures in communicating and keeping your body in balance. They must be protected. The following activity reviews the role of the skull, meninges, and cerebrospinal fluid and what happens when the brain gets scrambled.

Use two plastic containers with lids that are a little bit larger than an egg. Put an egg into each container. Fill one container with water. Firmly close each container with the lid. Shake the containers. Make your observations. Consider what part of this demonstration illustrates the skull, the meninges, the cerebrospinal fluid, and the brain. What was the role of the water?

TR 1. To review these concepts, you should complete questions 2, 3, and 7 on page 395 of your textbook.

Self-Check

These questions provide the opportunity to review and evaluate your understanding of the concepts in Lesson 2. Complete the questions, self-check your answers, and file your work in your course folder for reference when you study.

SC 3. The old saying or adage that “an elephant never forgets” appears to have some scientific basis. What area of the brain would you examine to begin researching about this saying? Describe two technologies that might be useful in this research.

SC 4. Five situations in which you may find yourself are described below. Identify the part of the brain involved in processing these situations.

1. _____ You are on a boat. A sudden wind comes up. The boat rocks violently. You feel dizzy and nauseated, and you want to vomit.
2. _____ You are in a restaurant. The waiter brings you the bill. You reach into your pocket to retrieve your wallet.
3. _____ You are on a hike in the mountains, and, all of a sudden, you come upon a grizzly sow with her two cubs. She rears up on her hind legs and growls menacingly. Your heart rate increases dramatically as well as your breathing rate.
4. _____ You see a backpack.
5. _____ You hear a dog barking.

SC 5. Use the diagram of a neural pathway through the spinal cord to answer the next question.

1. Explain what would happen if only Structure 2 were cut.
2. Explain what would happen if only Structure 4 were cut.
3. Explain what would happen if Structure 5 were cut.

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Reflect on the Big Picture

In this lesson you have examined how the sensations from your eyes and ears at that gathering described in the Big Picture are communicated to the cerebrum of the brain and the occipital and temporal lobes for interpretation. You have examined the medulla oblongata and its role in communicating automatic, involuntary responses such as the control of your breathing rate and heart rate. You have considered the role that the spinal cord plays in communication and the parts of the nervous system that protect these vital structures so that communication continues to establish homeostasis

Lesson Summary

In this lesson you have explored the following focusing questions:

• What are the main structures of the brain and spinal cord, what are their functions, and how are these functions co-ordinated?
• What happens when the information to or from the brain or spinal cord is disrupted or interrupted?

You have examined how all information about the external and internal environment is sent to the central nervous system, which consists of the brain and spinal cord. Various part of the brain, including the cerebral hemispheres, the four lobes of the cerebrum, the cerebellum, the medulla oblongata, the pons, and hypothalamus are responsible for receiving, sorting, interpreting, and co-ordinating information. The central nervous system (CNS) also initiates action in either the somatic or autonomic nervous systems.

The spinal cord functions to receive sensory information via the sensory neurons in the dorsal root and either relays the messages to the brain or initiates an action through a motor neuron in the ventral root. In Lesson 3 you will learn about these neurons and the reflex arc, a major function of the spinal cord.

In Lesson 7 you will learn how multiple sclerosis destroys the insulating layer around the long fibres of nerve cells so that nerve impulses cannot be transmitted quickly or cannot be transmitted at all in the central nervous system (CNS) and peripheral nervous system (PNS).  As a result, muscles cannot respond resulting in the tell-tale symptoms of this disorder.

Glossary

cerebellum: the brain region most involved in producing smooth, co-ordinated skeletal muscle activity; also involved in balance

cerebrum: the largest part of the brain which divides into the left and right hemispheres; contains centres for intellect, memory, consciousness, and language; it interprets and responds to sensory information and initiates the contraction of skeletal muscles

corpus callosum: the bundle of white matter that joins the two cerebral hemispheres; involved in sending messages from one hemisphere to the other effectively informing each half what the other half is doing

hypothalamus: a region of the brain located below the thalamus that acts as a centre of the autonomic nervous system responsible for the integration and correlation of many nervous and endocrine functions; helps to regulate the body’s internal environment, e.g., temperature; produces several hormones that are stored in the pituitary gland located directly below it

medulla oblongata: a part of the brain located between the pons and the spinal cord that controls involuntary responses such as heart rate, breathing rate, constriction and dilation of blood vessels, swallowing, and coughing

occipital lobes: one of the four lobes of the cerebrum, it receives and analyzes visual information that is sent to association centres for recognition of what is being seen

pons: a bridge-like structure that provides linkages with the neurons of the two halves of the cerebrum, the cerebellum, and the rest of the brain

somatosensory cortex: a part of the frontal lobes; receives sensory information from the limbs and body wall

spinal nerves: the 31 pairs of nerves that arise from the spinal cord; spinal nerves have both sensory and motor fibres

thalamus: a region of the brain located at the base of the cerebrum that regulates the flow of information from all the other parts of the nervous system and the sensory system

Lesson 1.1.3

Lesson 3—The Basic Units of the Nervous System: The Neuron and the Reflex Arc

Get Focused

When you were introduced to that special person who you hoped would be your new friend, you shook hands. You were ready with a big smile, but your response to the handshake surprised you!  Right away you withdrew your hand. The finger you sprained in basketball practice hurt. How embarrassing! Then you blushed, stammered, and felt like a fool.

But your body knows what it’s doing. This immediate “no-brainer” response is exactly that. Your brain is not involved in this response. You didn’t think about the response. Instead, your spinal cord has immediately responded to a communication of danger to your body. This is termed a reflex arc.

It’s the same as burning yourself on a hot stove, stepping on a tack, or swinging your leg up when the doctor taps your knee with a hammer. You have an immediate response, and shortly afterwards you have other responses. You may be embarrassed, cry out in pain, or respond in some other way.

Why is your initial reaction so fast?  Why do you become aware that the handshake hurt or that the stove was hot and respond afterwards?

In Lesson 3 you will study the structure and function of the neuron. Neurons are the specialized cells of the nervous system. These cells make it possible for you to see a person across the room, hear laughter, and smell a fragrance. You will examine how the neuron’s design can aid the speed of communication and how changes in its structure can result in interruption of communication.

In Lesson 1 you learned about the three basic types of neurons and how each one carries out a specific function in the basic neural pathway. Sensory neurons communicate messages from the body to the CNS. Interneurons process information and communicate messages through motor neurons to effectors to produce a response. In this lesson you will examine the features of a neural pathway called the reflex arc. You will come to understand how this communication pathway produces extremely rapid responses that protect and enable the survival of your body.

This lesson helps you to understand the following focusing questions:

• What are the structures and functions of the neuron? How do they support communication?
• What are the components of the reflex arc?

Module 1: Lesson 3 Assignment

Download a copy of the Bio 30 1.1.3 Assignment to your computer now. You will receive further instructions on how to complete this assignment later in the lesson.

Here is a tutorial video for this lesson that you can watch if it suits your learning style. Bio 30tut#1.1.3

1.1.3 page 2

Explore

In Lesson 1 you learned the divisions of the nervous system that sent information to the brain for processing.

In Lesson 2 you learned the specific parts of the brain that are responsible for processing information. You also learned that the brain communicates with structures in your body using motor neurons to produce a response. You will now learn about the structures and functions of the neuron, the basic cell of the nervous system.

Read

To help you understand neurons, read pages 368 and 369 of your textbook. Then read pages 370 to 372. You may wish to make summary notes and place your notes in you course folder for future study. It is important to include a labelled diagram of the neuron similar to the one on page 369 of your textbook.

You are now familiar with the receiving area called the dendrite, a cell body that carries out the life functions of the nerve cell, and the sending structure called the axon. Motor neurons communicate nerve impulses rapidly to effectors. They are myelinated, which means their axons are surrounded by Schwann cells. Schwann cells produce a fatty material called myelin sheath, which insulates the axon. In Lesson 7, you will learn how the nodes of Ranvier help to increase the speed of nerve impulse transmission. The axon terminals have many bulbous knobs that produce neurotransmitters. In Lesson 8, you will learn how neurotransmitters complete communication between neurons. These neurotransmitters are necessary because neurons are not physically joined together.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 372, fig. 11.9. Reproduced by permission.

Watch and Listen

To review the structures of the neuron, you may want to watch the video below.
Neuron Anatomy

Self-Check

You should now be able to describe the three types of neurons and describe the structures and functions of the parts of a neuron.

SC 1. Match the following functions to their respective structures indicated on the image below. Identify and write the name of the correct structure in the space provided corresponding to that structure’s number on the diagram.

Functions:

• performs life functions and relays messages to the axon
• the control centre of the cell
• receives input from other neurons of sensory receptors and transmits toward the cell body
• a fatty insulating layer that increases the rate of communication transmission
• gaps in the myelin sheath that increase the rate of communication transmission
• transmits nerve impulses away from the cell body
• a type of supporting nerve cell that wraps around axons in the peripheral nervous system and produces myelin

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 372, fig. 11.9. Reproduced by permission.

1.1.3 page 3 Lab

Module 1: Lesson 3 Assignment—Lab Part 1

Retrieve your copy of Module 1: Lesson 3 Assignment that you saved to your computer earlier in this lesson. Complete Lab Part 1. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Try This

To complete your understanding of the structures and their functions, complete the following table by selecting your response and dropping it into the correct space on the chart.  Check your answers, and store your work in your course folder.

Reflex Arcs

In some sports, you need to be fast. In hockey, for example, the forward has to be faster than the defender to score. The goalie has to react quickly to stop the puck. Did the goalie think about it, or did the goalie just do it?  Remember when you withdrew your hand because the handshake hurt? After you thought about what happened, you were embarrassed.  Some neurons are organized into special neural pathways that allow you to react before you are consciously aware of what is happening. These unlearned, unconscious, and very rapid pathways are called reflex arcs. The resulting behaviour is called a reflex. Do the following lab to understand more about reflex arcs.

Module 1: Lesson 3 Assignment—Lab Part 2

Retrieve your copy of Module 1: Lesson 3 Assignment that you saved to your computer earlier in this lesson. Complete Lab Part 2. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

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Watch and Listen

If you choose to further review reflexes, watch the video below

The Reflex Arc

You can also check out an interesting applet about reflexes from the BBC. You can use search words such as “bbc,” “schools,” “bite size,” and “bireflexarc.”

Self-Check

SC 2. To review your understanding of the reflex arc, write a step-by-step description of the process illustrated below using all the terms that you have learned, and then name the type of reflex. Check your answers, and file the assignment in your course folder.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 370, fig. 11.8. Reproduced by permission.

Self-Check Answers

SC 2.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 370, fig. 11.8. Reproduced by permission.

A withdrawal reflex. Receptors in the skin perceive the stimulus (the cactus). Sensory information is conducted from the senses into the spinal cord. Motor information is then conducted away from the spinal

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Reflect and Connect

When you were introduced to that special person, you quickly withdrew your hand from the handshake and then became embarrassed and blushed. To reflect on your knowledge from this lesson, trace the reflex arc that occurred when you withdrew your hand. Include a description of all the parts of the motor neuron that communicated with your muscles, and include a description of the role of the myelin sheath. Reflect on why your embarrassment and blushing happened later.

Lesson Summary

In this lesson you have explored the following focusing questions:

• What are the structures and functions of the neuron? How do they support communication?
• What are the components of the reflex arc?

You have examined the dendrites that receive information and pass it to the cell body. The cell body performs life functions and passes the information to the axon. The axon then passes information to its terminal. The axon has many specialized parts. The Schwann cell is a special support cell that wraps around the axon and produces an insulating fatty layer called myelin. Myelin insulation increases the rate of communication. The nodes of Ranvier also increase the rate of communication. You will study how communication rate is increased in Lesson 7.

Whether you withdrew your hand from the handshake or from a hot stove, or you stopped a fast-moving puck as a goalie, the response involved three types of neurons. The sensory neuron is able to receive stimuli from the sensory receptor and pass this information to the interneuron in the grey matter of the spinal cord. The interneuron is structured so that it can send nerve impulses to the brain for further processing, or it can stimulate a third type of neuron—the motor neuron. Motor neurons stimulate muscles and glands. A motor neuron also initiates quick involuntary response called a reflex. The reflex behaviour gives protection to the body and enables survival.

Diseases, such as Alzheimer’s, alter neurons in the brain and interrupt communication between nerve cells. Other diseases, such as multiple sclerosis, interrupt communication by destroying the myelin sheath and slowing or stopping nerve impulse transmission. You will learn more about these diseases as you study the mechanism of electrochemical communication through and between neurons in Lessons 7 and 8.

Injuries can also interrupt communication. If a sensory neuron were damaged, would you be able to detect the heat of the hot stove? If a motor neuron were damaged, would you be able to block the shot on net? Physiotherapy currently involves technologies to speed up the development of new sensory and motor neuron communication pathways.

Glossary

axon: the process that emerges from the cell body and conducts the nerve impulse away from the cell body; the axon may be a metre long in motor neurons

axon terminal: numerous endings found at the end of an axon; axon terminals are enlarged into knobs that are specialized for producing neurotransmitters

cell body: a part of a neuron that contains the nucleus and other cell organelles for carrying out the metabolic reactions of the nerve cell; relays the nerve impulse from the dendrites to the axon

dendrite: a branching  process of a neuron that receives input from other neurons or sensory receptors and transmits a nerve impulse toward the cell body

effector: one of the three types of muscle or a gland that responds to a nerve impulse

interneuron: a type of nerve cell found either in the brain or spinal cord that transmits nerve impulses from sensory neurons within the various parts of the brain or to motor neurons

motor neuron: a type of nerve cell that transmits nerve impulses toward an effector, which can be a muscle or a gland

myelin sheath: a fatty insulating layer that surrounds axons that greatly increases the rate of impulse transmission

neuron: a cell in the nervous system that generates and transmits nerve impulses; consists of dendrites, cell body containing the nucleus, and axon that may or may not have a myelin sheath

node of Ranvier: a tiny gap in the myelin sheath surrounding the axon of myelinated neurons; nerve impulse transmission occurs between nodes of Ranvier in what is called salutatory conduction which causes the increase in the speed of impulse transmission

reflex: an inborn, unlearned behaviour that results from the stimulation of a special neural pathway called the reflex arc

reflex arc: an involuntary neural pathway that consists of a sensory receptor, a sensory neuron, a control centre that can be either the brain or spinal cord, a motor neuron, and an effector that results in a reflex behaviour that usually has survival value

Schwann cell: a type of supporting nerve cell that is found in the peripheral nervous system and wraps around axons of neurons and produces the myelin sheath

sensory neuron: a type of nerve cell that receives stimuli and conducts an impulse toward the brain and spinal cord (central nervous system)

Lesson 1.1.4

Lesson 4—Sensory Perception: Taste, Smell, Touch, and Temperature

Get Focused

When you spot that attractive person across the room, maybe it’s his or her happy laughter that caught your attention. No wonder this person is happy! Can’t you just taste the pizza that they’re eating! Smell that aroma! You decide to approach, but the room suddenly seems a lot warmer. And then you extend your hand for the shake. This person’s skin feels cool for a short moment but then you withdraw your hand in pain. Now you’re embarrassed and the room really feels hot! All this information is increasing your breathing rate and heart rate. But the friend you’re with doesn’t seem as agitated as you are. Your friend doesn’t seem interested in the same person that you are and is not drooling over the pizza. Your friend’s perception is quite different from yours.

In this lesson, you will explore some of the senses that help maintain homeostasis by responding to environmental stimuli, both externally and internally. In Lessons 5 and 6 you will further explore the very important senses of sight and hearing. Sensory receptors, which are specialized neurons, receive stimuli such as taste, smell, touch, and temperature. You will learn about the special receptors for these senses, and how they communicate information to the brain for processing.

You will also examine how the brain processes information differently depending on your experiences. Investigators in accidents are often frustrated by eyewitness accounts of the same accident that are widely different. One person’s perception can be very different from that of another person. What do you see in the following images?

Do you see a wine glass, or do you see faces?

In this lesson, you will investigate the following focusing question:

• What information about the environment do the senses of touch, smell, and taste communicate to a person’s nervous system in order to maintain homeostasis?

Module 1: Lesson 4 Assignment

When you have completed all learning activities for this lesson complete the online assignment.

Bio30 1.1.4 online assignment

1.1.4 page 2

Explore

Crash Course  - Taste and Smell

Read

You can undoubtedly name the five basic senses that allow you to gather information about your environment—sight, smell, touch, hearing, and taste. To begin this lesson, read pages 406 to 409 of the textbook to explore the special type of cells, sensory receptors, that responds to stimulation from the environment.

You may choose to summarize this information as notes, as a mind map, as a chart, as a diagram, or as a podcast. Store your work in your course folder.

The senses are classified by the type of energy that stimulates the sensory receptors. You will discover how each sense has unique receptors for detecting changes. Types of sensory receptors include photoreceptors, mechanoreceptors, chemoreceptors, osmoreceptors, and thermoreceptors. These special nerve endings—or specialized nerve cells—convert the energy stimulus into electrochemical energy, a nerve impulse. You will study the electrochemical transmission of nerve impulses in Lesson 7 of this module.

These changes, called sensations, are communicated to specific areas of your brain, including the occipital, temporal, parietal, or frontal lobes of the cerebrum; the hypothalamus; and the cerebellum. As you saw with your friend, your brain doesn’t interpret information the same way to produce a perception.

 

Try This

Prepare three bowls of water—one with ice water, one with room temperature water, and one that has hot water as you would prepare for a hot bath. Put one hand in the ice water for several minutes and then put it into the room temperature water. How does the room temperature water feel in comparison to the ice water? Put the other hand into the bowl with the hot bathwater for several minutes. Now put this hand into the room temperature water. How does the room temperature water feel in comparison to the hot bathwater, and how does it compare to what you felt after the ice water? Did the temperature feel different? Was your perception of the room temperature water different after the immersion of your hand in the ice water and the hot bath water?

After holding your hand in ice-cold water for several minutes, the pain of the cold does not seem so excruciating. If the sensory receptors are repeatedly stimulated, sensory adaptation occurs where the brain filters out these sensations—this is why factory workers no longer notice the hum of machinery after working for a period of time. If you worked in a feed lot, do you think you would get used to the smell to the point where you would no longer notice the odour? Sometimes the brain perceives information differently from the sensory information it receives. Look at “Figure 12.4” on page 408 of your textbook for examples of some optical illusions.

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Taste

Pizza! You could just taste it. To understand the sensation of taste, read pages 425 and 426. You may wish to make summary notes or support your learning with diagrams. Store this information in your course folder for reference.

When you smelled the aroma of pizza, you started to salivate. This is a polite term for drool! Taste buds on the surface of the tongue can only detect a taste when chemicals are dissolved on the tongue so that chemoreceptors can start an impulse to the brain. There are four basic tastes—salty, sweet, sour, and bitter. Try resting a sour candy on various parts of your tongue as you see in “Figure 12.25” on page 426 of the textbook. You’ll get the idea of where various taste receptors are located on your tongue!

Your taste likes and dislikes appear to have a homeostatic value, or an indicator for what the body may need to retain or restore homeostasis. A liking for sugar and salt helps satisfy the body’s need for carbohydrates, minerals, and some amino acids.  Because many poisons and spoiled foods are bitter, a person’s dislike of bitter food is an instinctive, protective response.

Self-Check

Complete the Taste Reception Handout below. After you have checked your answers, store your work in your course folder for reference when you study.

Taste Reception Handout

1. What four basic tastes do most scientists agree are sensed by most people? Name at least one food that illustrates each taste.
2. Supertasters are people whose sense of taste is significantly more sensitive than the average person. Hypothesize how the anatomy of taste reception may differ in a supertaster as compared to a normal person.
3. Explain why the taste bud is considered a “sense organ.”
4. Hypothesize whether the taste buds which are sensitive to saltiness are the same taste buds which are sensitive to bitterness or sweetness.
5. Draw a flow chart to illustrate the taster’s steps from taste reception to interpretation.

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Smell

Ah, the scent of pizza. Or maybe the scent of a fragrance as you approached that special person. It makes you want to get closer. But the friend that you’re with is sneezing a lot and his nose and eyes are running. Are your senses communicating perceptions that are quite different than those which your friend is perceiving? To learn more about smell and what it communicates, read page 426 of your textbook.

Smell, much like taste, detects chemicals in solution. Olfactory receptor cells are stimulated by chemicals only when in solution. A sensory nerve communicates this information to the frontal and temporal lobes of the brain. Cells in the olfactory epithelium produce a continuous secretion of mucous in which molecules of airborne chemicals dissolve. Mucous is continuously secreted to flush away old odour chemicals so that new odour chemicals may gain access to the receptors. Smells associated with dangers such as smoke, natural gas, or skunk musk trigger the sympathetic nervous system. The perception of unpleasant odours can trigger sneezing or a gag reflex. Your friend’s perceptions are very different from yours!

Self-Check

Complete the Smell Reception Handout below. Self-check and store your work in your course folder.

Smell Reception Handout

1. Label the structures 1 to 14.
   

   Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 427, fig. 12.26. Reproduced by permission.

2. What has to happen to airborne chemicals like those of a rose before they can be smelled?
3. What is the function of structure 10?
4. What is the purpose of the olfactory cilia on the olfactory cell (receptor cell)?
5. Where is the nerve impulse initiated?
6. Outline the specific sensory pathway involved in smelling a rose.

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Touch

You are about to be introduced. The room is so hot. Your hand is so sweaty that it feels sticky. Wow, this person has a firm handshake. Your brain tells you that the finger you sprained in basketball practice is hurting from the pressure of the handshake. You wince in pain and pull away quickly. To understand more about touch, read pages 427 to 429 of the textbook.

The mechanoreceptors for touch are all over the body, but they aren’t evenly distributed. Consider how sensitive your fingertips and lips are compared to the back of your hand. They can detect light touch, pressure, pain, and high and low temperatures. From the previous activity, when you put your hand into the ice water and held it there, it wasn’t long before you felt the freezing sensation. How would it feel if it was your elbow in the freezing water? Do you think you could keep your elbow in the cold water longer than your hand?

Some Human Sensory Receptors in the Skin

Inquiry into Biology u5_S12.27_p.429, from McGraw Hill Reproduced by permission.

In the graphic above, the figure marked "free nerve endings" is a free dendrite ending as found in thermoreceptors (hot and cold receptors) as well as some pain receptors. The remaining figures have enclosed dendrites in capsules. These sensory receptors are mechanoreceptors that sense touch, pressure, vibration (on and off pressure), and stretch stimuli. Krause’s end bulb shown by the third figure on the left and Meissner’s corpuscle shown on the top right are sensitive to light touch but are located in different parts of the body.

From the diagram, can you hypothesize which type of receptor is more concentrated in your hand than in your elbow, which would explain why your hand was more sensitive to the cold water?

Try This

Bend a paper clip into a U-shape with the two ends about 2 mm apart.  Close your eyes, and gently push down on the palm of your hand with the paper clip. Then gently press the paper clip on your shoulder, and your elbow. In which location could you distinguish the two prongs as being separate?

What do your results suggest about the number of mechanoreceptors for touch in the palm of your hand, relative to the number in your shoulder? You might want to look at Figure 12.27 on page 429 to review the various types of touch receptors.

Self-Check

Complete the self-check activity below.

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Reflect and Connect (optional)

The sensations of smell and taste are closely related. In Biology 20 you learned about the respiratory system. Based on your knowledge of physiology, reflect on why is it more difficult to taste or smell food when you have a cold? Choose one of the following formats to illustrate how Lesson 4 fits with the previous three lessons:Prepare a concept map, a diagram, or a podcast. Remember to link the sensory receptors to the appropriate parts of the central or peripheral nervous system, and include the specific parts of the brain that are involved.

OR

In the Get Focused section of this lesson, you were asked to consider sensing the smell of pizza or a person’s fragrance, the taste of pizza, the temperature of the room, or the pain in your hand. Write a poem, make a comic strip, or draw diagrams which illustrate the communication and processing of one of these sensations. Include in your example the stimulus, the type of sensory receptor involved, the sensory neuron, and the part of the brain that is used.

Submit your work to your teacher.

Self-Chec

To ensure that you have mastered the concepts of this lesson, try these self-check multiple-choice questions. Check your answers and file your work in your course folder for a future review.

1. Identify the statement that best compares sensation to perception.

1. A sensation occurs when nerve impulses from the sense organs reach the cerebral cortex; perception is an interpretation by the brain about the meaning of sensations.
2. A sensation occurs when nerve impulses from the sense organs reach the spinal cord; perception is an interpretation by the spinal cord of the meaning of sensations.
3. A sensation occurs when nerve impulses from the sense organ bypass the spinal cord and go directly to the brain; perception is an interpretation by the sensory receptors of the meaning of sensations.
4. A sensation occurs when nerve impulses from the sense organs reach the cerebral cortex; perception is an interpretation by the peripheral nervous system of the meaning of sensations.

2. You walk into a pizza restaurant and immediately notice the smells associated with cooking pizza. After a few minutes, you no longer notice these odours. This phenomenon can be explained by a process called

1. sensory accommodation
2. a reflex arc
3. sensory adaptation
4. sensory perception

3. Which of the following is an INCORRECT match between the sensory receptor and the stimulus that it responds to?

1. photoreceptor—light energy
2. chemoreceptor—pressure
3. mechanoreceptor—sound waves
4. thermoreceptor—change in radiant energy

4. The olfactory receptors in a dog’s nose would be classified as

1. photoreceptors
2. mechanoreceptors
3. chemoreceptors
4. proprioceptors

5. Which of the following structures would you NOT mention if you were tracing the path involved in tasting something sweet?

1. taste bud
2. olfactory receptor cell
3. sensory neuron
4. parietal lobe of cerebrum

Use the following information to answer multiple-choice questions 6 and 7.

The tips of the fingers are sensitive enough to discriminate raised points on a surface, as well as the locations of these points. Knowing this, in the nineteenth century Louis Braille invented the Braille system of reading for blind people. Each letter of a language alphabet is represented by up to six raised dots. A blind person who has learned the Braille system can read up to 50 words a minute.

6. Will a person preparing Braille script have to know if the blind reader is left-handed or right-handed and, thus, change the order of the script accordingly?

1. No, because the sensations from both the right hand and the left hand are carried by the spinal cord into the same hemisphere of the cerebrum.
2. No, because the sensations received separately by the left and right cerebral hemispheres from the right and left hands are integrated before they are interpreted into language.
3. Yes, because the sensations from the right and left hands are carried to the left and right cerebral hemispheres, respectively, and therefore the information is interpreted in reverse order.
4. Yes, because the movements of the right and left hands are initiated by opposite sides of the cerebral cortex.

7. This sentence can be read using the eyes, but it can also be read using the fingertips if the sentence is printed in Braille. This fact illustrates that

1. the brain can form the same meaning from different sensations
2. nerve impulses initiated by touch are identical to nerve impulses initiated by sight
3. receptors for touch and receptors for sight respond to the same environmental stimuli
4. the lobe of the brain that receives sensory stimuli from the eyes is the same lobe that receives sensory stimuli from the fingers

Reflect on the Big Picture

Lesson 4 focuses on how you gather information about your environment through the senses of taste, smell, and touch. In the “Big Picture,” you gathered information about the scents of pizza and fragrance, the pain of a handshake, and the temperature of a room, This information had to be received by your sensory receptors and communicated through sensory nerve impulses to different lobes of the cerebrum, such as the temporal and occipital lobes.

The brain interprets this information and causes your body to feel something or to do something in response. If the perfume is pleasant you may move closer to the person, inhale more deeply, and you may feel pleasure. But remember the sneezing response that your friend had to the odours? Using the information from this lesson, reflect on these possible responses to a stimulus. Store this response in your course folder.

1.1.4 page 7

Lesson Summary

In this lesson you investigated this focusing question:

• What information about the environment do the senses of touch, smell, and taste communicate to a person’s nervous system in order to maintain homeostasis?

 In this lesson you investigated how the body is able to gather information about the external and internal environment in order to maintain a constant internal environment, or homeostasis. The senses are the functional categories that scientists use to classify how the body gathers information. You studied the specialized neurons that respond to stimuli (types of energy). These specialized nerve cells are identified as

• mechanoreceptors

• chemoreceptors

• thermoreceptors

• photoreceptors 

The sensory receptors for taste and smell are chemoreceptors, while touch receptors are mechanoreceptors.  Hot and cold sensory receptors are thermoreceptors. The sensory receptors are able to initiate a nerve impulse that is transmitted through a sensory neuron to a specific part of the brain that is able to interpret the information. The brain initiates a response that maintains or returns the body to homeostasis. In Lesson 4 you learned how taste, smell, and touch reception occurs and how a nerve impulse is initiated so that the information can be transmitted to the brain for interpretation.

Lesson Glossary

chemoreceptors: a sensory receptor that transmits information about the solute concentration in a solution or about individual kinds of molecules in solution

mechanoreceptors: a sensory receptor that detects physical deformations in the body’s environment associated with pressure, touch, stretch, motion, and sound

olfactory (receptor) cell: a neuron located in the olfactory epithelium that is specialized to receive chemical stimuli and to initiate a nerve impulse

perception: the interpretation of sensory information by the cerebral cortex

photoreceptors: sensory receptors that respond to light stimuli, allowing people to see images as well as colours

sensation: the reception and processing by the brain of a nerve impulse sent by an activated sensory receptor

senses: specialized mechanisms or functions by which an organism is receptive and responsive to a certain class of stimuli which are typically external as in the senses of sight, hearing, touch, and pain but also internal as in sensing the temperature of the blood, or the levels of carbon dioxide

sensory adaptation: the tendency of sensory neurons to become less sensitive when they are repeatedly stimulated

sensory receptor: a cell or a group of cells located in various parts of the body that is specialized to receive stimuli that provide information about the body’s external conditions (through sight, hearing, taste, smell, or touch) and internal conditions (such as temperature, pH, glucose levels, and blood pressure)

tactile reception: the receiving of stimuli involving touch, pressure, vibration, and stretch

taste bud: a sensory organ composed of a taste pore, taste cells, and sensory fibres of a sensory neuron involved in initiating taste sensations

thermoreceptors: a sensory receptor that detects heat or cold

Lesson 1.1.5

Lesson 5—Photoreception: The Eye

Get Focused

When you are in a room full of people, you are constantly gathering information about those around you. You respond to the sights, smells, sounds, and even the feel of the room. Your eyes are one of the best sensory tools you can utilize to gather information from your external environment. In fact, 80 to 90 percent of all sensory information is received by your eyes. Consider this fact the next time you find yourself in a new environment or situation as you work to make sense of the information you perceive.

Your ability to interpret the visual information you receive is a complex process dependent on the physiology of the eye and a complex series of reactions which are not completely understood. In Lesson 2 you studied the parts of the brain, should now be capable of making the connection between how a nerve impulse is transmitted to the occipital lobe of the cerebrum and the interpretation an image. The work you did in Lesson 4 will help you understand how perception results from the cerebral cortex interpreting the meaning of the sensory information received.

How much do you remember about what you saw after you left a room full of people? If you were to compare your perceptions with another person who was also in the room, do you think that your visual memories would be the same? As you work through this lesson you will learn more about eye function and communication, and how these processes influence your perceptions of what you see.

In this lesson you will explore the following questions:

• What are the major parts of the eye?
• How do these parts function?
• How do these parts work together to communicate with the nervous system in order to facilitate the integrated act of seeing?

Module 1: Lesson 5 Assignment

 Bio30  1.1.5 assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style. 

** The Self-Check and Try This questions in this lesson are not marked by the teacher; however answering these questions will help you review important information and build key concepts that may be applied in future lessons. You can respond to these mentally, write out your response, or record your answer in any other way that works for you. **

1.1.5 page 2

Explore

The Structures of the Eye

Read

The eye is an amazing organ! It contains many structures that must all be functioning properly in order for you to see. Several of these structures refract and focus light before it even reaches the different photoreceptors that make up the structure called the retina. Once these photoreceptors are stimulated by light energy, they convert this energy into an electrochemical nerve impulse. Sensory neurons in the optic nerve communicate this nerve impulse to interneurons in the occipital lobe of the brain where visual information is then processed. To understand the parts of the eye and how they contribute to vision, read pages 410 to 412 of the textbook. As you work through the reading, keep track of the vision disorders and their respective symptoms. You will need this information for an upcoming assignment.

It is always an excellent idea to support your understanding of the concepts you are learning with a diagram. You may choose to include diagrams in the work you will store in your course folder. Should you choose to include diagrams, be sure to include any brief descriptions of the functions of any structures, as well as brief summaries of the steps of different pathways.

 Crash Course - Sight

Try This

Here are three Try This activities you can use to verify your understanding of the parts of the eye and their functions, as well as vision issues related to the dysfunction of one or more of these structures. Please note that there is a choice of two possible activities indicated under each Try This.

TR 1.

Review the structures of the eye and their functions by dragging and dropping the terms provided into their respective places in the following chart.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 411, fig. 12.2. Reproduced by permission.

Accommodation video

The ciliary muscle and suspensory ligaments are excellent examples of how the sympathetic and parasympathetic nervous systems work together to establish homeostasis in vision. By changing the shape of the lens they allow for light rays to be refracted, bent differently allowing you to focus on the words of this sentence as you read it, or on the words on a poster you see on the far wall when you look up. This process is called accommodation and can be summarized by the following activites.

TR 2.

Complete the following by putting the lists provided in the correct order. You may wish to look at Figure 12.10 on page 412 of the textbook to help you figure out the correct order of events.

1. Sympathetic Nervous System: 

   • ciliary muscle relaxes

   • tension on suspensory ligament

   • tension pulls on lens

   • lens flattens

   • focus on far objects

    

   Place the numbered list above in the correct order:
   
   ___, ___, ___, ___, ___

    

2. Parasympathetic Nervous System:
   
   

   • ciliary muscle contracts

   • tension on suspensory ligament relaxes

   • less pull on lens

   • lens bulges

   • focus on near objects
     
     

   Place the numbered list above in the correct order:
   
   ___, ___, ___, ___, ___

OR

Watch and Listen

Review the accommodation reflex by watching the video

The Lens video

As we grow older, the flexibility of our lenses decreases. As a result, many people must wear reading glasses to focus the details of nearby objects. Hyperopia is the term used to describe the ability to see distant objects clearly, and the inability to focus on objects that are close. You may have already heard the more common term for this condition, which is farsightedness. Inversely, myopia is the condition of being able to clearly see objects that are close, but not being able to focus on objects that are farther away. The common term for myopia is nearsightedness. To learn what enables the lens to change its shape in order to successfully focus an image, which will allow you to better understand the conditions mentioned above, read pages 412 and 413 of the textbook. When you have finished the reading, make summary notes on the concepts learned. You may also choose to support this information with a labeled diagram. Store your information in your course folder for review purposes.

Another condition that affects the lens is cataracts, while astigmatism is a condition which affects the cornea. These conditions distort your vision. Remember to add them to your table of disorders. At the end of this lesson, you will submit your table to your teacher for assessment.

To develop your mastery of the concepts you have been reading about, do questions 1 to 3 and 5 on page 418 of your textbook. You may discuss your responses with your teacher if you wish.

The Retina and Supporting Structures

The inner layer of the eye consists of the delicate retina which contains two different types of photoreceptors called rods and cones. Directly in line with the middle of the lens, is an area of the retina called the fovea centralis, or fovea. This small, depressed area is where the cones are most highly concentrated. Cones are the photoreceptors that are sensitive to different colours, whereas rods are sensitive to light intensity. Rods are more spread out on the periphery of the retina. The neural fibres from the retina form the optic nerve, which is the sensory pathway out of the eye. The spot where the fibres come together is the blind spot, or optic disc.

Organisms that see well at night, like deer and cats, have a reflective layer similar to spray paint on surface of the choroid layer. This structure is called the tapetum. The tapetum increases the animal’s sensitivity to low levels of light and helps these animals see at night. This layer also causes the eyes of these animals to appear iridescent or reflective in the dark.

In front of the lens is the anterior chamber filled with aqueous humour. This transparent, watery fluid is produced by the ciliary body. If the aqueous humour is not successfully drained from the anterior chamber, its buildup will eventually result in the eye disorder called glaucoma. Behind the lens is the posterior chamber filled with vitreous humour—a faintly clear to amber-coloured gel-like fluid. Both the aqueous and vitreous humours will aid the refraction of light to a small degree.

1.1.5 page 3

Module 1: Lesson 5 Assignment

Retrieve your copy of Module 1: Lesson 5 Assignment that you saved to your computer earlier in this lesson. Complete Part 1. Save your completed assignment in your course folder. You will receive instructions later in this lesson on when to submit your assignment to your teacher.

Self-Check

Complete the following crossword puzzle to consolidate your understanding of the different structures of the eye and their functions:

Read

The Retina

You should now be familiar with the different structures of the eye and have a good understanding of each structure’s role in vision. As such you should understand which structures are needed to alter and focus light on the retina. The retina is the key structure by which light energy is converted into an electrochemical impulse. This sensory impulse is then communicated to the brain via the optic nerve. When it reaches the occipital lobe of the brain, the information which was transmitted as an impulse is processed by inter-neurons. To further understand how the retina converts light energy into electrochemical impulses, read pages 414 – 416.

Study the diagram below to locate the four layers of cells in the retina:

pigmented cells

- closest to the choroid

- specialized to form the tapetum in some animals.

rods and cones
- the actual photoreceptors.
- located above the pigmented layer

You might expect the photoreceptors to be in the direct path of incoming light, but the rods and cones are further covered by layers of transparent neurons;

bipolar cells
- activated by rods and cones

 ganglion cells
- closest to the vitreous humour.

In the following diagram, note the direction of the light striking the retina. Light travels through the transparent layer and strikes the rods and cones. These photoreceptors are then prompted to stop emitting an inhibiting neurotransmitter substance, which you will learn about in lesson 8. The rods and cones can then communicate an electrochemical message first to the bipolar cells and then on to the ganglion cells. Axons of all ganglion cells of the retina converge at the back of the retina to form the optic nerve which carries impulses to the brain. Mouse over the diagram to see each part of the diagram highlighted

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 415, fig. 12.16. Reproduced by permission.

Rods and Cones

From the diagram, you may have noted that rods are the most abundant photoreceptors in the retina. They are necessary in distinguishing shades of black and white as well as distinguishing movement. Cones respond to specific wavelengths of the visible spectrum which allows us to see colour. Cones are also needed for acute vision as they are capable of finer discrimination of detail in bright light than are rods.

Based on your new knowledge of rods and cones could you develop a hypothesis explaining why the eyes of birds that roost at night have only cones, whereas the eyes of owls and bats that are active at night have only rods?

You have also read about colourblindness. There are three types of cones – red sensitive, green sensitive, and blue sensitive. One reason that we can see so many variations of colour is that the sensitivity ranges of these receptors overlap. For example, yellow light stimulates both red and green cone cells, but if the red cones are stimulated more strongly than the green cones, we see orange instead of yellow. Look at Figure 12.14 on page 414. If you see the *, you have normal colour vision. If you see a number 8, you have the full range of colour vision. If you see a number 3, you have red-green colour blindness. Can you explain the varying degrees and types of colourblindness in terms of the types of cones? Colorblindness is a genetically inherited trait that will be studied in more detail in the genetics module of this course (Unit C).

TR 4.

To review the concepts of vision, watch the video.

Colour Vision

How the Eye Works

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Rods and Cones Initiate Nerve Impulses

Rods and cones contain pigments called photopsins that absorb light and start chemical changes. Cones contain three different pigments called iodopsins. Rods have only one type of pigment called rhodopsin. When rhodopsin absorbs light it is bleached and it breaks down into opsin, a colourless protein, and a derivative of Vitamin A called retinal. This chemical change in the rods initiates a nerve impulse in the bipolar cells, which transfer the impulse to the ganglions. The ganglions, which make up the optic nerve, then transmit the impulse to the occipital lobe of the cerebrum to be processed.

Your eye then restores opsin and retinal to rhodopsin, but this takes energy in the form of ATP. This reverse reaction also requires vitamin A. Knowing this, could you explain why your eyes get strained in poor lighting, why nightblindness is caused by Vitamin A deficiency, and why you should eat your carrots?

Light and Dark Adaptation

Rhodopsin is extremely sensitive to light. Even starlight causes some molecules of rhodopsin to become bleached. In high intensity light, rhodopsin is broken down almost as fast as it is remade. In such a situation, the rods become nonfunctional and the cones take over completely. For example, think about what happens when the lights are turned on after a movie. You are momentarily “blinded” and all you see is white light. Your pupil constricts in a reflex in order to protect your retina from the bright light. Within a minute or so, the cones become sufficiently stimulated to take over once again. Over the next few minutes, visual acuity and colour vision improve. On the other hand, adaptation to low light occurs when you go from a well-lit area into a dark one. At first you see nothing but velvety darkness because your cones have stopped functioning due to lack of light, and your rods are not functioning because they have been bleached out by the bright light. Once in the dark, rhodopsin is remade and accumulated so that low intensity light can again stimulate the rods. During adaptation to both light and dark, reflexive changes occur in the pupil of the eye.

The Pathway to the Brain

Try This

Did you know that each eye sees thing differently?  Each eye has it’s own area of “blindness”, the blind spot. To find your blind spot, try the activity in Figure 12.17 on page 416.

The information you receive from each eye is communicated through the optic nerve to the brain. Your brain processes this information into one image for you without gaps or blind spots. The optic nerves enter the optic chiasm on the ventral, front of the brain (see Lesson 2). In the X-shaped optic chiasma some axons from each eye cross over to the opposite side of the brain while others continue to their respective side of the brain. The crossing over of about half of the sensory fibres ensures that each half of the occipital lobe receives the same image or part of the visual field as viewed by each eye. However, keep in mind that each eye will see the image from a slightly different angle. Study Figure 12.18 on page 416, or the illustration provided here very carefully in order to better understand vision interpretation by the brain.

Depth perception is possible due to the “fusing” or the superimposing of the slightly different images from the two eyes by the visual cortex. This creates a three-dimensional image. Thus, by working together, the eyes provide slightly different angles of view that allow the brain to estimate distance.

The image that was reversed and inverted in the lens is at his point interpreted correctly.

1.1.5 page 5

Try This 6

To review, you may choose to do questions 5 and 7 on page 418 of the text

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 416, fig. 12.18. Reproduced by permission.

Module 1: Lesson 5 Assignment—Defect/Disorder Table

As you worked through this lesson, you learned about the different structures of the eye and about their functions in facilitating vision. You were also introduced to some disorders that are the result of one or more of these structures malfunctioning.

Self-Check

To ensure that you have mastered the concepts of this lesson, you may wish to do the self test which includes a numerical response question as well as a closed written response question. This is an excellent opportunity to practice for the types of questions that will be presented on the Diploma Exam.

Use the following information to answer question 1:

Visual Interpretation

The brain integrates visual information from both eyes. Some of the steps in the visual pathway are shown below. Please note that these steps are NOT in the correct order and that NOT all steps are part of the visual pathway.

1. rods and/or cones change light energy into a nerve impulse

2. nerve impulse travels to the temporal area of the brain for sorting

3. nerve impulse travels to the occipital lobe of the cerebral cortex for interpretation

4. ganglion cells are stimulated

5. nerve impulse leaves eye via the auditory nerve

6. light energy enters the eye and strikes the retina

1. In the four spaces below, record the number of the four steps that are part of the visual pathway. Record the steps in the correct order in which they occur during the visual pathway.
   
   ____  ____  ____  ____
2. There are two chief types of light sensitive cells (called X and Y in this question) in the healthy human retina but they are not evenly distributed. An investigation on the distribution of sensory cell types X and Y across an area of the retina (shown as PQ on the diagram below) was developed.
   
   
   
   The relative numbers of cell types X and Y were more or less constant except in positions R and S. Using relative numbers, the following graph indicates the relative frequency of sensory cell type X along the axis PQ.
   
   

1. 1. Identify cell type X
   2. Identify cell type Y
   3. What structure is represented by region R?
   4. What structure is represented by region S?
2. Copy the graph above and clearly superimpose a curve to indicate the relative frequency of cell type Y along the axis PQ.

The diagram below represents the different states of the iris in bright and in dim light.

3. 1. What structures are represented by M and N?
   2. Briefly explain what causes the iris of eye B to have a different appearance than that of eye A.

1.1.5 page 6

Reflect and Connect (optional)

Most people are left-brain dominant but some are are right-brain dominant. The dominance of one side of your brain over the other affects how you perceive what you see. Your brain is crucial in the integration, interpretation, and perception of what you see. Two people looking at the same thing may see it very differently!

Choose one of the following written response questions. Reflect upon the question and then respond in paragraph format. Store your response in your course folder for future reference:

Look at a picture, clock, or some distinctive object located on the other side of the room. Cover or close one eye. Concentrate on that object for a few moments. Now, cover or close the other eye. What happens to the image when you switch from viewing it first with one eye, then with the other? What does this simple experiment illustrate about vision?
 
or

The actual visual sensation which we experience is not always an exact representation of the visual information that is picked up by our eyes. This is because the brain is susceptible to all sorts of past and present influences that modify our perception. Visual information modified by the brain image so that we see the image that our brain is conditioned to see. Do an Internet search using the term "old woman young woman perception." Your search engine will display a number of illustrations. Follow a link to an illustration that plays on perception. Look at the illustration. What do you see? It is possible to see a young woman, or it is also possible that you see an old woman. Perhaps you are able to see both. The image that you see, or your perception of the image depends on your brain and your life experiences.

Discuss

Would you have laser surgery to change the shape of your lens? Many nearsighted people are now considering laser surgery to eliminate the need for glasses. Research this technology and identify any possible benefits and risks associated with the procedure. Address and explain at least 2 benefits and 2 risks of the procedure. Post your findings on the discussion board. Ask classmates to comment on, based on your findings, whether or not they would have the surgery. You may prepare your findings as a chart that lists the pros and cons of the procedure, or you may record your findings in point form.

Reflect on the Big Picture

In this lesson you continued exploring the senses. Photoreception, or the sense of vision, involves the largest number of sensory receptors in the body.The eyes gather approximately 80 – 90% of the information about our external environment and transmit it to the brain. In the Big Picture you saw a person across the room. As you walked toward them, their image was kept in focus by what reflex? (as “pop-up text-the accommodation reflex”). The (“pop-up text - papillary reflex”) adjusted the amount of light entering the eye. (“as pop-up text –Cones”) were activated to allow you to see colours. The (as pop-up text - occipital lobes of the cerebral cortex) integrated and interpreted this information. Based on this information that you received and the visual perception that you formed, you decided to say hello to the person.

At this point, you should research any relationship between Alzheimer’s disease and vision. Store any additional information in your course folder in preparation for your module assessment. Keep the following key questions in mind when reviewing:

• What are the major structures of the eye?

• How do these structures function?

• How do they communicate with the nervous system to support the integrated act of seeing

Lesson Summary

In this lesson, you explored the following focusing question:

What are the major parts of the eye, how do these parts function, and how do they communicate with the nervous system to support the integrated act of seeing?

Through your readings, through the dissection you completed, through your research, and through the video presentations you learned about the structures of the eye and their functions. By exploring the structures of the photoreceptors, called the rods and cones, you learned how a nerve impulse is initiated and transmitted to the occipital lobe of the cerebrum. It is there that the sensations are interpreted. Things like: the frequency of nerve impulses, the origin of the impulse in the retina, and previous experiences and memory all factor into the interpretation of light stimuli. Not everyone will interpret these sensations in the same way as observed with optical illusions. Many common visual defects and/or disorders affect the functioning of the eyes and impede proper vision. Numerous technologies have been devised to correct these disorders.

Lesson Glossary

accommodation: the process of changing the shape of the lens from round and fat to thin and flat and vice versa so that light can be focused on the retina to accommodate vision of objects near and far away

adaptation: the process by which the iris adjusts the diameter of the pupil based on light conditions thus controlling the amount of light that enters the eye and strikes the retina

anterior chamber: space in front of the iris and behind the cornea that is filled with aqueous humour

aqueous humour: a clear, watery fluid in the anterior chamber of the eye that maintains the shape of the cornea and provides oxygen and nutrients for the surrounding cells, including those of the lens and the cornea

astigmatism: uneven curvature of the cornea or lens resulting in uneven focusing which in turn results in poor vision

bipolar cells: specialized sensory nerve cells located in the retina that are stimulated by either rods or cones; cones mostly have a one to one ratio with bipolar cells, whereas several rod cells may communicate with one bipolar cell

blind spot: the area at the back of the eyeball that is deficient in rods and cones; the area where the sensory fibres come together to form the optic nerve

cataracts: cloudy or grey-white areas on the lens caused by deterioration of the protein composing the lens; prevents the passing of light to the photoreceptors of the retina

ciliary muscle: a ring of muscle behind the iris that is attached to the lens by suspensory ligaments; involved in changing the shape of the lens

choroid: middle layer of the eyeball that lies between the sclera and retina which is highly vascular and heavily pigmented; absorbs stray light rays not detected by the

photoreceptors of the retina

colour blindness: an x-linked inherited disorder that results in nonfunctional or deficient cone function; inability to see certain colours such as red, green, or blue

cones: one of two types of photoreceptors in the retina of the eye that is sensitive to different wavelengths of light and are thus responsible for distinguishing colour; there are three types of cones – one sensitive to red light, one to blue light, and one to green light; they are responsible for acute vision, or distinguishing detail

cornea: transparent portion of the sclera, located at the front of the eye; allows light to enter the eye and, in the process, bends the light rays so that they can be focused on the retina

depth perception: the ability to see in three dimensions

fovea centralis: an area of the retina that is located directly behind the centre of the lens; has a very high concentration of cones which makes this part of the eye responsible for great visual acuity

glaucoma: disorder caused by the malfunction of ducts that drain excess aqueous humour from the anterior chamber; the resulting pressure created by excess aqueous humour ruptures delicate blood vessels in the eye and causes deterioration of cells in the eye due to lack of nutrients; can result in blindness if left untreated

ganglion cells: special sensory neurons that communicate with bipolar cells in the retina to transmit a nerve impulse to the brain; these cells have long axons that converge at the back of the eye to form the optic nerve

hyperopia: farsightedness, or the inability to focus objects that are close; caused by an eyeball that is too short which causes light to be focused behind the retina

iodopsin: the general name of any of the three visual pigments found in cone cells that is stimulated by light to initiate a nerve impulse

iris: the circular, coloured part of the eye which is a circular muscle formed from the choroid; it contracts and dilates to change the diameter of the pupil

lens: clear flexible structure located behind the iris which focuses light on the photoreceptors of the retina

macular degeneration: a disorder that results in the degeneration and death of cells (cones) in the fovea centralis and the surrounding area (macula) causing a loss of vision in the centre of the field of view but not at the periphery; the person sees a black spot in the centre

myopia: nearsightedness, or the inability to focus objects that are far away; caused by an eyeball that is elongated which causes light to be focused in front of retina rather than directly on it

optic nerve: a collection of sensory neurons that carries sensory information from the photoreceptors to the brain

opsin: a protein that is the result of the decomposition of rhodopsin

pupil: hole in the middle of the iris; its diameter is adjusted by the iris to control the amount of light entering the eye

retina: the innermost layer of the eye which contains the photoreceptors

retinal: a derivative of Vitamin A (retinol) that is the result of the decomposition of rhodopsin; is instrumental in initiating a nerve impulse

rhodopsin: a visual pigment found in rod cells that is decomposed by light into opsin and retinal; the change initiates a nerve impulse

rods: one of two types of photoreceptors in the retina of the eye that are sensitive to light intensity and detect movement; they do not distinguish colour

sclera: the white, tough, protective outer layer of the eye that helps gives the eyeball its shape; sometimes called the white of the eye

tapetum: a reflective layer of cells located in the choroid, and in some cases directly in the retina,) of some nocturnal animals; increases the likelihood of dim light stimulating the photoreceptors

vitreous humour: transparent, amber coloured, jelly-like fluid in the posterior chamber of the eye which helps to maintain the shape of the eyeball

Lesson 1.1.6

Lesson 6: Mechanoreception—The Ear

Get Focused

Where is your cell phone? You can hear it ringing but you can’t find it. There’s no point in asking your parents where it is. They can’t hear it. Older people who have some hearing loss may not be able to hear the high tone of the mosquito ring on your phone. Your cell phone is ringing in class, but your teacher can’t hear it. Could this also be an example of the mosquito ring tone? Being able to hear sound is an important factor in communication, however not all people are able to hear the same sounds.

The ear is also an important structure involved in balance. That queasy sensation you felt when you were watching the truck beside you slide down the hill last winter while your vehicle pulled forward was the result of conflicting information from your eyes and your inner ear. When you have an inner ear infection, communication between your eyes and ears is interrupted and you may not be able tell whether you’re laying down or standing up. You may become dizzy and suffer vertigo, the illusion of spinning in space.

In this lesson, you will explore such phenomena as you address the following focusing questions about the ear and mechanoreception:

• What are the major structures of the ear?

• How do these structures function to facilitate your response to sound in the environment?

• How do these structures function help you maintain your balance in a constantly changing environment?

Module 1: Lesson 6: Assignments

Once you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio 1.1.6 online assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style. 

** The Self-Check and Try This questions throughout this lesson are not marked by the teacher; however these questions provide you with the practice and feedback that you need to successfully complete this course. **

1.1.6 page 2

Explore

Crash Course - Hearing and balance

Read

Outer Ear

There are three major regions in the ear: the outer ear, the middle ear, and the inner ear the most obvious structure of the outer ear is the pinna. Some animals can move their pinnae to maximize trapping sound waves. By moving its pinnae, the fennel fox, pictured on the right, can pinpoint with great accuracy the direction from which a sound originates. For many animals survival can be dependent on early detection of sound. In humans, the muscles of the pinna are vestigial, or nonfunctional, and we can’t move our pinnae. However, people sometimes cup their ear with their hand to simulate an enlarged pinna in order to hear better. Do you know anyone who can actually move their pinnae?

© Khirman Vladimir/Shutterstock

Read page 420 and note "Figure 12.20."

Self-Check

• auditory canal: a short channel that conducts sound waves from outside the ear to the tympanum (eardrum); amplifies or makes sounds louder

  tympanum: a round elastic structure located in the middle ear that vibrates in response to sound waves; also called the eardrum or tympanic membrane

  Locate the pinna and the auditory canal. What is the function of these structures?

• What did cupping the ear accomplish?

• The auditory canal also produces ear wax. What is the purpose of this wax?

• What else does the auditory canal do?

• Wax build up can be a cause of conductive deafness. Look at the picture on the right. What is the syringe used for?

• The auditory canal ends at the tympanum, also known as the tympanic membrane, or more commonly the eardrum. Can you hypothesize what the function of the tympanic membrane might be?

To review the structures found in the outer ear and their functions, read pages 419 – 420 in your textbook. Summarize your findings in a table similar to the one below. File the table in your course folder for later access.

The Structures and Functions of the Outer Ear

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Middle Ear

The middle ear extends from the tympanum, or tympanic membrane, to the oval window. The structures of the middle ear are specialized to conduct and amplify the mechanical vibrations that sound waves produced. The tympanic membrane is connected to the ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup). In the following reading, consider how the tympanic membrane vibrates, causing the ossicles to act as a lever conduction, thus amplifying vibrations through the middle ear.

When you have a cold and are suffering from a throat infection, your throat infection can quickly develop into a terrible ear ache. It may feel like your ear drum will break or burst from the pressure that is building in the middle ear. In some serious cases, ear infections can cause the eardrum to rupture, which can results in partial hearing loss.

Read page 420 and note Figure 12.20.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 420, fig. 12.20. Reproduced by permission.

What structures make up the middle ear? Be careful here. The diagram seems to show that the semicircular canals are part of the middle ear. This is not so! The middle ear is bordered by the tympanum and the oval window.

Did you notice the Eustachian tube? Taking into account the location of the Eustachian tube, can you hypothesize what events may have occurred as a result of your throat infection that lead to the bursting of your ear drum? Have you ever notice your ears “pop”? Your ear drum “popping” indicates the process of pressures equalizing on each side of the eardrum. This is common when you’re in an unpressurized plane, under water, or travelling in the mountains. Yawning, chewing, or swallowing can help equalize these pressures.

At this time you may wish to make summary notes, a mind map, a table of structures and functions like the one below, or you may wish to prepare a diagram of the ear with all structures and functions labeled. File your work in your course folder.

The Structures and Functions of the Middle Ear

Self-Check

SC. To help you understand and apply the concepts on the outer and middle ear, complete the following questions. Remember that complete sentences using Biological vocabulary are necessary at the Biology 30 level. Check your answers and file the questions in your course folder. If you are unsure about an answer, consult with your instructor.

1. Describe what would happen if a person poked a hole in their tympanum while trying to remove ear wax.

2. On a plane ride, where the pilot is expecting to encounter significant turbulence, the attendants may give hard candies to the passengers. Explain the physiological basis of this gesture.

3. Propose a hypothesis to explain why humans do not have enormous, moveable pinnae like some animals.

4. Explain why middle ear infections are common.

1.1.6 page 4

Read

The Inner Ear

Sound has been collected, transmitted, and amplified, but you haven’t heard anything yet. The inner ear is responsible for converting mechanical stimulation to a nerve impulse to be communicated to the brain. The inner ear also converts mechanical stimulation into information on balance to be interpreted by the brain.

Read page 420 and study Figure 12.20 Can you determine which structures make up the inner ear? The inner ear is composed of two organs: one for hearing and one for balance. Note the structures for hearing which include the oval window, cochlea, round window, and auditory nerve. Note also the utricle, saccule, and semi-circular canals which function in balance. You may wish to record the information in summary notes, a concept map, or as additions to your diagram or table. Store your work in your course folder.

The Structures and Functions of the Inner Ear

Read

Organ of Corti

Special parts of the inner ear must be functional in order to facilitate hearing. From your study so far, you have not encountered the mechanoreceptors of these parts and how they function in hearing. Mechanoreceptors are specialized receptor cells that detect a stimulus such as pressure or vibration.

As you study these parts of the inner ear, you will discover why people can lose their range of hearing as they age.

Read the section on the inner ear and the organ of Corti on pages 420 and 421. Study Figure 12.21 on page 420 which shows a cross section of the cochlea and the location of the organ of Corti (blown up on the far left of the figure). The receptors for sound waves are located inside the organ of Corti. Make summary notes or summarize the functions of the structures of the organ of Corti in a table similar to the following. File your work in your course folder.

The Structures and Functions of the Organ of Corti

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Try This

To ensure that you understand the mechanisms of the inner ear involved in hearing, complete the drag-and-drop activity below. If you have any questions about the inner ear ask your instructor.

Self-Check

SC. The following self check will help you review the concepts of the outer, the middle, and the inner ear. Consult with your instructor if you were not able to give complete answers. Store your answers in your course folder.

1. Imagine that you are a sound wave. In order, describe the structures of the ear that you would encounter, starting with the outer ear and finishing with the Organ of Corti.

2. What happens to the energy of sound waves, which travel through air, once they reach the tympanum?

3. How is the surrounding medium of the inner ear different from that of the middle ear? What has to happen to the vibrations in the middle ear in order to accommodate this difference?

4. What is the role of the hair cells located in the organ of Corti?

5. Nerve impulses initiated in the organ of Corti are sent to which part of the brain?

  Self-Check

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 420, fig. 12.20. Reproduced by permission.

1. Which three parts of the ear are involved in amplifying sound waves?
2. The initiation of nerve impulses occurs in which structure?
3. Which structure first directs sound waves into the ear?
4. Which structure aids in the equalization of pressure between the outer and inner ear?
5. Which structure is most affected if pressure is not equalized?
6. Where is the organ of Corti located?
7. Middle ear infections affect which structure?
8. In the ear, which structure is considered analogical to the optic nerve in the eye?
9. Where are the wax glands located?
10. Which structure causes the ossicles to vibrate?

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Read

Hearing Pitch and Loudness

You have likely been to a concert, listened to your iPod, or perhaps you play a musical instrument, so you are probably familiar with high and low pitch sounds. However, do you know how or why you are able to hear high or low pitch sounds? How are you able to distinguish between yelling and whispering? To understand how we hear, read pages 421 – 424. When you have finished, make summary notes, a concept map, or a flow chart for your course folder.

Try This

To assure your understanding of the concepts of pitch and loudness, answer the following questions in full sentences. If you are unsure of any of the concepts, consult with your instructor. File your exercise in your course folder.

1. Define frequency.
2. What is pitch? What is the relationship between pitch and frequency?
3. What is the amplitude of a sound wave? How is the intensity or loudness of a sound related to the amplitude of a sound wave?
4. Each of the sounds described below predominantly illustrates either pitch or loudness. Classify each as one or the other according to its main feature.

1. whine of a mosquito
2. sound of a low note on the piano
3. sound of a jackhammer breaking up a cement sidewalk
4. sound of jet plane taking off
5. growl of a dog

Read

Loudness, Pitch, and the Organ of Corti

As you have read on pages 421 to 424, the hair cells in the organ of Corti are sensitive to the frequency (pitch) as well as to the amplitude (loudness) of sound waves. The basilar membrane closest to the oval window (where frequency is 20,000) is narrow and stiff as shown in the diagram below. It responds to high frequency sound waves.The basilar memrane by the apex of the cochlea (where frequency is 20) is wide and flexible. It responds to low frequency sound waves.

In the lab, you will be examining the differences between pitch and loudness. Notice in the diagram that the wider basilar membrane furthest from the oval window and closest to the apex or tip of the cochlea responds to lower frequency sound waves. Different hair cells are stimulated by different frequencies. In the diagram, the numbers correspond to the range of frequencies that humans can hear. In comparison to humans, dogs can hear very high sounds in the range of 40,000 Hz Reflect on how we use this knowledge in the use of a dog whistle. Mice can hear in the range of 80,000 Hz. And elephants can hear sounds as low as 16 Hz. Hair cells at either end of the basilar membrane can be damaged over the years and they do not regenerate. How would this damage affect the range of your hearing as you age? If you guessed that the ability to hear high and low sounds deteriorates, you were right.

Try This (optional)

You may choose from one of the following exercises:

Demonstrate your understanding of the concepts on how sound is perceived by answering the following questions in complete sentences.

1. How is the brain able to perceive sounds of higher or lower pitch and softer or louder sounds?

2. Mice and dogs can hear sounds in the range of 40, 000 - 80,000 Hz whereas elephants hear sounds as low as 16 Hz. Describe how the cochlea of these animals might be modified as compared to the human cochlea.

3. Why are elderly people often not able to hear very high pitched sounds?

OR

Do questions 6, 18, and 19 on page 432 of the textbook.

1.1.6 lab

Module 1: Lesson 6 Assignment—Investigation :

Investigation

Types and Causes of Deafness

Types of Deafness

Conductive hearing loss occurs when sound vibrations don't go from the air around a person to the moving bones of the inner ear as well as they should. If something is blocking the ear canal, like ear wax, there is a conductive hearing loss. If there is fluid inside the inner ear where the bones are, like the fluid from an inner ear infection, there is a conductive hearing loss. If the bones of the ear get a buildup of calcium, from a disease perhaps, and they can't move as freely as they need to, there is a conductive hearing loss. Generally, conductive hearing loss doesn't cause a total inability to hear, but it does cause a loss of loudness and a loss of clarity. In other words, sounds are heard, but they are weak, muffled, and distorted.

Neural hearing loss (Nerve deafness) occurs when the auditory nerve, which goes from the inner ear to the brain, fails to carry the sound information to the brain. Neural hearing loss can cause a loss of loudness or a loss of clarity in sounds.

Mixed hearingloss is a combination of conductive and neural hearing losses.

Causes of Deafness

Heredity. Some people are born deaf. Usually the cause is unknown. Sometimes people will say it's because of something that happened to the mother during her pregnancy, but this is often just guessing. Although deafness does sometimes "run in families," deaf parents often have hearing children and hearing parents often have deaf children.

Diseases of the Ear

Ear infections are diseases which can cause fluid or mucus to build up inside the ear. If pressure builds up inside the ear, the eardrum is less flexible than it should be. As the ear heals, the fluids drain out of the ear or are absorbed into the body. Some hearing may be lost during the infection; it may or may not return when the infection is healed.

Otosclerosis is a common cause of hearing loss. Although in the past people have thought that it was caused by diseases such as scarlet fever, measles, and ear infections, in fact these have nothing to do with its development. It is a hereditary disease in which portions of the middle ear or inner ear develop growths like bony sponges. The disease can be in the middle ear, the inner ear, or both places. When it spreads to the inner ear a sensorineural hearing impairment may develop. Once this develops, it is permanent. If it is in the stapes bone, in the middle ear, it can cause a conductive hearing loss. The amount of hearing loss depends on the amount of otosclerosis in the area.

Meningitis is an inflammation of the membrane(called the meninges) that surrounds the brain and the spinal column. Meningitis itself doesn't cause deafness, but since the brain is so close to the ears, sometimes the inflammation of the meninges can cause the inner ear to become inflamed also, and this can result in deafness.


Injuries of the Ear

Punctures of the Eardrum. Hearing loss can be the result of a hole in the eardrum, which could be caused by either injury or disease. The eardrum is the thin membrane that separates the ear canal and the middle ear. The middle ear is connected to the throat by the eustachian tube, which relieves the pressure in the middle ear. So a hole in the eardrum causes a loss of hearing and sometimes fluids can drain from the ear. Luckily the eardrum usually heals itself, although it can take a few weeks or months. While the eardrum is healing, it must be protected from water and from further injuries. If the eardrum doesn't heal by itself, it may need surgery. The amount of hearing that is lost depends on the size of the hole in the eardrum and a lot of other things.

Injuries which can perforate the eardrum include:

• Foreign objects, such as Q-tips or hairpins, which are pushed too far into the ear canal.
• Explosions, which cause an abrupt and very big change in the air pressure, which can cause an eardrum to tear.
• Car wrecks, fights, and sporting injuries.

Nerve Damage. Damage to the auditory nerve can also be the result of an injury or a disease. Injuries can happen in auto accidents or falls. The result of nerve damage is that the electrical signals of sounds do not get transmitted from the ear to the brain.

Loud Noises. A very common cause of deafness is repeated or long-term exposure to loud noises. This is why heavy equipment operators, firefighters, factory workers, and especially rock musicians suffer hearing losses after years of their work. Usually a single incident of exposure to loud noises will not cause deafness, but a repeated exposure to loud noises over a period of time will often cause moderate to severe hearing loss.

Going Beyond

• If you found the investigation interesting and you want to learn more about hearing loss, you may want to investigate tinnitus, which is a disorder experienced by many hearing impaired people.

1.1.6 page 8

Read

Homeostatic Imbalance in Hearing

In today’s world, health care workers are very concerned that your generation will experience increased numbers of hearing loss as it ages. Deafness can be defined as one of two main types: conduction deafness or perception deafness.

Self-Check

Answer the next two questions that deal with hearing loss. Check your answers.

1. What is meant by the term “deaf”?

2. State the parts of the ear that have been damaged or are non-functional in someone with
   
   
   1. perception (nerve) deafness
   2. conduction deafness

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Maintaining Balance

The ear has an important function in your ability to maintain balance. The inner ear has three additional structures known as the semicircular canals, the utricle and the saccule that are responsible for maintaining balance. When you twirl on the dance floor, ride a rotating ride at the midway or suffer through a rough boat ride, the semicircular canals are working overtime. This is called dynamic equilibrium or rotational equilibrium. That queasy feeling you experienced when you pulled ahead of the truck slipping backwards on the icy hill, or that similar feeling you get when a fast-moving elevator comes to an abrupt stop is the result of nerve impulses from the utricle and saccule. This is called static equilibrium or gravitational equilibrium. Some impulses from the vestibular apparatus travel to the spinal cord, where body position can be adjusted by reflex action. Other impulses are sent to the cerebellum, where other reflexive muscular coordination occurs. Further impulses move to higher centres in the cerebrum involved in the control of eye movement. Input from the eyes is very important in maintaining balance. To show this, try closing your eyes and standing on one leg!

To understand how the body maintains balance, choose one of the following two options. You may summarize the information in any format you choose and store this information in your course folder.

Read page 424.

OR

Watch and Listen

Watch the following videos
Hearing and Balance

Utricle and Saccule

Self-Check

After reading the text and/or watching the video segments, test your understanding of the concepts by completing the following questions. File your work in your course folder. If you do not understand a particular concept, consult your instructor.

1. Describe the structures of the inner ear that are involved in maintaining balance.
2. Explain how the structures of the inner ear allow for dynamic (rotational) equilibrium.
3. Explain how static (gravitational) equilibrium is attained.

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Self-Check

Study the lesson and then test how well you understand the concepts by doing this test. This self test reflects the kind of questions that you will encounter on the Diploma examination. The first 7 questions include both numerical response and multiple choice style questions. After doing these, you can autocheck to see how well you did.

Numerical Response Question

Use the following diagram to answer the next two questions.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 420, fig. 12.20. Reproduced by permission.

1. Match the following structures with those labeled on the picture of the human ear. Record the number from the diagram in the space that corresponds below. (Record all four digits of your answer in the spaces below.)
   
   __________              ___________           ___________           __________
   semicircular               tympanum                  middle ear               cochlea
   canals
2. The structure that is primarily responsible for maintaining dynamic equilibrium is represented by
   
   
   1. 1
   2. 2
   3. 3
   4. 4
3. Which pair gives an INCORRECT function for the structure(s)?
   
   
   1. Eustachian tube – equalization of pressure
   2. cochlea – initiation of nerve impulses
   3. round window – dissipation of pressure waves
   4. utricle and saccule – dynamic equilibrium
4. Place the following events in the correct sequence after the first event stated below: Record the four digits of your answer below.
   
   

   __________              ___________           ____________         __________

   First Event: Sound waves push against the tympanum.

   1. Tiny hair-like cells in the organ of Corti respond to vibrations by stimulating sensory fibres

   2. Vibrations are amplified by the ossicles.

   3. The basilar membrane begins to vibrate.

   4. The oval window receives vibrations from the ossicles

Use the following information to answer the next two questions.

A cochlear implant is very different from a hearing aid. Hearing aids amplify sound. A cochlear implant is designed to compensate for damaged or non-functional parts of the inner ear. When hearing is functioning normally, complex parts of the inner ear convert sound waves in the air into nerve impulses. These impulses are then sent to the brain, where they are interpreted and recognized as sound. A cochlear implant works in a similar manner. It electronically finds useful sounds and then sends impulses to the brain. Sounds heard through an implant may sound different than sounds heard without, but it enables many people to communicate orally in person and over the phone who would not be able to do so without such a device.

5. Identify the specific structure(s) of the inner ear that the cochlear implant is intended to replace.
   
   
   1. tympanic membrane
   2. hair cells located on the basilar membrane
   3. round window
   4. ossicles
6. Identify the specific structures of the ear that have the same function as a hearing aid.
   
   
   1. tympanic membrane and ossicles
   2. hair cells and sensory fibres on the basilar membrane
   3. round and oval windows
   4. vestibular apparatus
7. Which of the following statements is INCORRECT with respect to hearing in humans?
   
   
   1. The hair cells of the organ of Corti are able to distinguish both the frequency (pitch) and amplitude (loudness) of sound waves.
   2. The hair cells of the organ of Corti are able to detect sound within the frequency range of 0 Hz to 20 Hz.
   3. High frequency sounds most strongly stimulate the hair cells closest to the oval window.
   4. Low frequency sounds most strongly stimulate the hair cells farthest from the oval window.

1.1.6 page 10

Reflect and Connect

In the Big Picture for this module, you were introduced to the nervous system and communication. Hearing is a very important part of communication. If perception of sound had not been communicated to your brain, how would you have interpreted the events that occurred while you were in the room with your friends?

Reflect on the Big Picture

What might your perceptions have been like in a room like that described in the Big Picture without your being able to hear the laughter, the people talking and perhaps the music playing? How does music at the beginning of a movie help to communicate the tone of movie? What kinds of music communicate dangerous, scary, funny, or romantic scenes? Before a big game, athletes use “pump-up” music for motivation! How do you think Beethoven, who was deaf, was able to successfully convey all of the moods in his music? Sounds in today’s very noisy world are contributing to hearing loss in many people. Knowing now the things you have learned in this lesson, you may be more aware of the volume at the next concert, or the next wedding that you attend. Reflect on the precautions that you could take to protect your ears and your hearing the next time you mow the lawn, ride a snowmobile, listen to your iPod, or use power machinery. What do you notice when you shut the machine off? Could this be a indication of what you should do to safeguard your hearing? In the Get Focused section of this lesson, you could hear the mosquito ringtone of your phone. As you grow older, will you always be able to hear this ringtone, the music you love, the sounds that ensure your survival or those that bring you pleasure? Judging by your own habits when it comes to hearing,do you think that you might have to wear a hearing aid at some point in your lifetime?

Module 1: Lesson 6 Assignment—Part 3

Hearing Technologies Research

Discuss

Consider the following scenario:

Ethan was very excited to have landed a job as an assistant baggage handler at the airport. He got to drive the baggage train, and load and unload suitcases and parcels from airplanes. However, he found that the ear protection that he was supposed to wear was hot and cumbersome. He took it off whenever he could and sometimes he forgot to put it back on when the big jets came in or took off. After two years on the job, he began finding that was having difficulty hearing. It was suggested that he purchase a very expensive new type of hearing aid that would greatly improve his hearing. Ethan was very upset because his medical plan did not pay for hearing aids.

• Do you think that hearing aids should hearing aids be covered by our medical plans? Keeping Ethan’s story in mind, suggest several reasons why they should and several reasons why they should not. Using the discussion board, share and discuss the reasons supporting your argument as well as those that counter your argument. Share your final “for and against” reasons with your instructor. 

Lesson Summary

In this lesson, the following focusing questions were investigated:

• What are the major parts of the ear that facilitate your response to sound in the environment?

• How do the structures of the ear impact your ability to maintain balance within your changing environment?

You should now be familiar with the structures and functions of the outer, middle, and particularly the inner ear. Located in the inner ear, both the cochlea, adapted for hearing, and the vestibular apparatus, adapted for maintaining balance, rely on specialized hair cells to change mechanical energy of sound or movement to the electrochemical energy of a nerve impulse. The structures of the outer and middle ear conduct and amplify sound waves so that pressure waves can be created in the cochlea of the inner ear. The frequency of a sound wave results in your perception of pitch, whereas the amplitude (height) of the sound wave results in your perception of loudness. Conduction deafness and perception (nerve) deafness result when there is a dysfunction in the hearing apparatus.  Both dynamic and static balance are maintained by the vestibular apparatus, which includes the semicircular canals, the utricle, and the saccule.  Technologies, such as hearing aids and cochlear implants have been developed to help us deal with hearing loss.

Lesson Glossary

amplitude: the extent of a vibration; see intensity

auditory canal: a short channel that funnels sound waves from outside the ear to the ear drum or tympanum; it amplifies sound waves thereby making sounds louder

auditory nerve: a nerve composed of sensory fibres from the organ of Corti the vestibular apparatus which conducts impulses to the temporal lobe of the cerebrum

basilar membrane: one of two parallel membranes that comprise the organ of Corti in the inner ear (the other being the tectorial membrane); hair cells are attached to it

cochlea: contains the organ of Corti which functions to convert the mechanical energy of sound waves into a nerve impulse

dynamic balance (rotational equilibrium): balance resulting when the head and body are moved or rotated

 Eustachian tube: tiny passageway extending from the middle ear to the throat (pharynx); plays an important role in equalizing air pressure on both sides of the tympanum

 frequency: number of wavelengths per given time; number of waves that pass a given point in a given time

 hair cells: sensory mechanoreceptors attached to the basilar membrane in the organ of Corti within the inner ear

incus (anvil): the middle in the sequence of the three ossicles located in the middle ear; connected to the malleus and the third ossicle (stapes); part of a lever system which amplifies sound waves

inner ear: one of the three regions of the ear that is located deepest into the head and consists of a fluid filled chamber which contains the semicircular canals, the utricle and saccule, and the cochlea

intensity: measurement of the difference between compressed and rarefied areas of a sound wave used in physics; corresponds to amplitude of a wave

loudness: subjective interpretation of sound intensity

malleus (hammer): the first in the sequence of the three ossicles located in the middle ear; connected to the tympanum and the second ossicle (incus); part of a lever system which amplifies sound waves

middle ear: one of the three main regions of the ear which begins just past the tympanum and consists of a chamber containing three tiny bones (ossicles) called the malleus (hammer), the incus (anvil), and the stapes (stirrup);  leads into to a minute opening called the Eustachian tube

organ of Corti: contains hair cells that detect vibrations in the fluid of the inner ear and initiates a nerve impulse that is transmitted to the auditory nerve

ossicles: three tiny bones located in the middle ear that are connected to each other , to the tympanum, and to the oval window; involved in amplifying sound waves

otoliths: tiny particles of calcium carbonate found in the utricle and saccule that contact the hair cells of these structures and stimulate them

outer ear: one of the three main regions of the ear (outer ear, middle ear, and inner ear) which consists of the pinna and the auditory canal; ends at the tympanum or eardrum

oval window: a membrane covered opening located between the chamber of the middle ear and wall of the inner ear; the stapes (stirrup) is attached to it and transmits sound waves by it to the inner ear

pinna: the outer flap of the ear composed of skin and cartilage and shaped so that it funnels sound waves into the auditory canal, thereby enhancing them

pitch: corresponds to the frequency of a sound wave

round window: a membrane covered opening located between the chamber of the middle ear and the inner ear, and below the oval window; functions in dissipating sound waves in the inner ear

sebaceous gland: tiny glands in the auditory canal that produce wax

semicircular canals: three tubes that are situated at right angles to one  another; contain mechanoreceptors that detect head and body rotation; responsible for dynamic balance, or rotational equilibrium (rotational equilibrium dynamic balance), which is the balance that is established in response to the head and body being moved or rotated

sensory neurons: nerve cells that are stimulated by hair cells in the organ of Corti to conduct messages toward the temporal lobe of the brain

sound: pressure disturbance beginning at a vibrating object (source) and spread out by a medium such as air

sound wave: a series of compressions and rarefactions resulting in an S-shaped curve or sine wave

stapes (stirrup): the third in the sequence of the three ossicles located in the middle ear; connected to the second ossicle (incus) and the oval window; part of a lever system which amplifies sound waves and causes vibrations in the fluid of the inner ear

static balance (gravitational equilibrium): balance resulting from changes in the position or the movement of the head in one direction; usually in response to gravity

tectorial membrane: one of two parallel membranes (the other being the basilar membrane) that is found in the organ of Corti; during the transmission of sound waves, the basilar membrane vibrates and causes the sensory hairs to flex against the tectorial membrane

tympanum: a round elastic structure that vibrates in response to sound waves; also called the eardrum or tympanic membrane

utricle and saccule: tiny chambers in the inner ear that contain hair cells which respond to changes in head position with respect to gravity and movement in one direction; responsible for static balance, or gravitational equilibrium

vestibule: fluid-filled area of the inner ear located between the semicircular canals and the cochlea; contains the utricle and saccule

Lesson 1.1.7

Lesson 7: The Nerve Impulse—Transporting the Message

Get Focused

Your cell phone is ringing—how did you know?

In this lesson, you will explore how this special type of cell, the neuron, which makes up the pathways and structures of the nervous system, communicates messages through its cell structure.

You will also examine how communication is interrupted by diseases such as multiple sclerosis.

Once you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio30 1.1.7 online assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#1.1.7
 
** The Self-Check and Try This questions throughout this lesson are not marked by the teacher; however these questions provide you with the practice and feedback that you need to successfully complete this course. **

1.1.7 page 2

Explore

Read

The Neuron at Rest

In the previous lessons you examined how communication pathways throughout the Nervous System called sensory pathways sent information about taste, smell, touch, sight, and sound to the brain. Different lobes of your brain processed this information, and motor pathways communicated appropriate responses to your effectors. You can review how this works in the flow chart below:

Sensory receptors → sensory pathway → lobes of brain → motor pathways → effectors

Now you will examine some characteristics of the special type of cell, the neuron, that makes up the nerves in these pathways. As part of this exploration you will need to understand how messages are communicated through the neuron from dendrite to terminal end. To do this, you must investigate the neuron membrane and explore the role of sodium and potassium ions as well as negatively charged particles such as proteins and chloride ions which surround the neural membrane.

To understand the characteristics of a neuron at rest and a nerve impulse, read pages 372 – 374 of the textbook. Be sure to make summary notes for your course folder. Study Figure 11.12 on page 374 of your textbook, which describes how the sodium potassium ion pump works. Summary notes and a similar chart in your course folder will prove to be invaluable in mastering these concepts.

Action potential Crash Course

 Sodium Potassium Exchange Pump

• Identify two characteristics of active transport.
• In which direction are sodium ions moved across the neuron membrane by the sodium potassium exchange pump?
• In which direction are the potassium ions moved?
• Where is the carrier protein of the ion exchange pump located?
• What causes the shape changes in the carrier protein?
• Where is ATP used?

You should now know that sodium ions become more concentrated outside the neuron and potassium ions become more concentrated inside the neuron. The net result is that the interior of the neuron (intracellular fluid) becomes negatively charged compared to the exterior (extracellular fluid) which becomes positively charged. When this occurs, the neuron is said to be polarized. This can be verified by inserting a tiny electrode into the axon of the neuron and touching another to its surface. Usually there is a difference in charge or a resting membrane potential of approximately 70 mV. This may vary from cell to cell and in different situations. Use the illustration of the polarized or resting neuron below to review these concepts.

Where is the greatest concentration of the red circles, representing the sodium ions? If you guessed outside the membrane, you were right. Where is the greatest concentration of the blue circles, representing the potassium ions? If you guessed inside the membrane you were correct. Besides movement of potassium ions by the ion exchange pump, what other way can you see in the diagram that facilitates movement of potassium ions towards the outside of the cell? If you guessed diffusion and carrier molecules you were correct. What do the black circles represent? If you guessed chloride ions you were correct. Why are there no black circles on the exterior of the neuron? If you guessed that the membrane is impermeable to chloride ions you were correct. What is the net charge on the exterior of the axon membrane? If you guessed positive you were correct. What is the net charge on the interior of the axon? If you guessed negative you were correct.

Watch and Listen

The following video segments may help you to understand the processes of message transmission:

Neuron Structure and Function

Sodium Potassium Pump

Action Potentials

Self-Check

In your own words, answer the following questions in order to determine whether or not you understand the concepts to this point. When you have finished, autocheck your answers, make any corrections, and file your work in your Biology 30 Course Folder for later review.

1. What is the term used to describe the resting state of a neuron?
2. Explain what the resting membrane potential is and why it is significant to the functioning of the neuron.
3. Identify and explain the three factors that contribute to maintaining the resting membrane potential.
4. Describe the distribution of sodium ions, potassium ions, and negatively charged particles in a resting neuron.
5. What is meant by a “resting potential of -70mV”?

1.1.7 Page 3

Watch and Listen

You should now realize that communication through the neuron involves a series of action potentials.

When a neuron becomes sufficiently stimulated by a threshold stimulus, the point of stimulation becomes depolarized and the depolarization spreads along the length of the unmyelinated neuron. This depolarization is created by a rapid change in membrane permeability and a corresponding change in the balance of ions maintained at the resting state. Depolarization can be likened to a burning fuse. The flame, like the wave of depolarization progresses along the wick in one direction. However, in the fuse, the wick is burned and cannot be used again. In the neuron, after the wave of depolarization, an immediate recovery called repolarization occurs. To understand the next steps in communication, read pages 374 – 377. Summary notes in your course folder will prove to be invaluable in mastering these concepts. You may wish to create your own illustration of these events and add it to your course folder for review.

Watch and Listen

Animation 1: Action Potential Propagation in an Unmyelinated Neuron - Action potential video

• What is the net charge on the outside of a resting neuron?

• What is the net charge on the inside of a resting neuron?

• Describe the action potential.

• What keeps the action potential going along the axon of the neuron?

• What are localized electrical circuits?

• Why does the action potential proceed only in one direction?

• What is an absolute refractory period?

Animation 3: Voltage Gated Channels and the Action Potential - Voltage Gated Channels Video

• Draw an illustration of the voltage-gated Na+ channel and the inactivation gate.

• Draw an illustration of the voltage-gated K+ gate.

• Describe how depolarization occurs and what happens in repolarization.

Watch and Listen

The Refractory Period and the All or None Principle

Throughout this module, you have discovered that normal communication involves periods of interruption. In this case, while repolarization was occurring, there was no chance for communication. Another sodium inrush could not occur. This brief period when no stimulus can elicit a response is called the refractory period. Its duration is usually only one to two milliseconds.

The stimulus that begins the influx of sodium ions and starts depolarization has to be of certain intensity in order to open the voltage-gated sodium channels. Once this voltage shift is reached, depolarization begins. It doesn’t matter if the voltage shift is higher because once the gates are open a wave of depolarization occurs. It is just like lighting the wick in our fuse analogy—either it ignites and begins to burn or it does not ignite. Much the same, if the stimulus is not strong enough to open the gates in the neuron membrane, nothing happens. The voltage shift needed to open the sodium gates is called the threshold potential. This ability of the neuron to only respond to a disturbance in electrical charge of a specific threshold value is called the all or none response. Like your ski bindings which either release, or they don’t, the neuron either transmits the wave of depolarization, or it doesn’t. In an all or none response, there are no in-betweens. Like falling dominos, once the wave of depolarization begins, it results in an impulse.

To view watch the videos below

All or None Principle

Nerve Impulse

1.1.7 page 4

Self-Check

TR 1. One way to model the action potential is to line up several dominoes and initiate a cascade event, in which each successive domino knocks down the next domino.

1.  In this model, the hand provides the initial energy. What provides the initial energy in a neural impulse?

2. The finger has to contact the first domino just hard enough to get it to fall. Which response does this represent in a real neuron?

3. Once the dominoes start to fall, they all fall in succession. What does this action represent in the real neuron?

4. The dominoes always fall in one direction. Contrast this with the direction of impulse transmission in a real neuron.

5. No matter how many times the dominos fall, they always move at the same speed and intensity. What principle does this represent in the real neuron?

Check your answers before proceeding further in this lesson.

Self-Check

After reading the text, watching the animations, and comparing a nerve impulse to the falling of dominoes, do you feel confident that you understand and can explain the changes that are involved in the transmission of a nerve impulse? Complete this next activity without consulting any references. Check your answers, make corrections and/or additions and file these handouts in your Biology 30 Course Folder for easy access when studying.

Depolarization of the Neuron Handout

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), BLM 11.1.9. Reproduced by permission.

1. What is illustrated by Number 1? Explain what is happening in Number 1.
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________

    

2. What is shown by Number 2? Explain what is happening to Number 2 at this time.
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________
   
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3. What is indicated by Number 3? Identify one characteristic of Number 3 and identify the function of Number 3.
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________
   
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4. What structure is shown by Number 4? Explain its function.
   
   _____________________________________________________
   
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   _____________________________________________________
   
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5. What are 5 and 6? What is their function in nerve impulse transmission?
   
   _____________________________________________________
   
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Repolarization of the Neuron Handout

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), BLM 11.1.9. Reproduced by permission.

1. What is shown by Number 1 in this diagram? How do you know this?
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________
   
   _____________________________________________________

    

2. What is happening in Number 2 in this process?
   
   _____________________________________________________
   
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3. What is the function of Structure 3?
   
   _____________________________________________________
   
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4. What functions does Structure 4 serve in the process illustrated?
   
   _____________________________________________________
   
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5. What do 5 and 6 tell you about Structure 4?
   

   _____________________________________________________
   
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If your answers are similar to those in the self check key, you are ready to submit an assignment to your teacher to show your understanding. If you do not understand the concepts, then you need to access your teacher for further discussion before attempting the assignment.

1.1.7 page 5

Read

Watch and Listen

Myelin and Impulse Transmission

In lesson 4, you learned about the basic structures of the neuron. You discovered that some axons are wrapped in Schwann cells that produce a fatty material called myelin. Myelin acts as an insulator. In the following video clip, you will see the significance of insulation to communication in myelinated nerves versus unmyelinated nerves.

Watch this video before proceeding with the next section.

Myelinated vs. Nonmyelinated Neurons

In the video, you saw that myelin is not present on all nerve cells. Myelinated neurons can conduct nerve impulses over 100 metres per second whereas unmyelinated neurons are much slower, with speeds of only 0.5 metres per second. Even though the axon of the myelinated neuron is not in contact with the sodium rich extracellular fluid outside the neuron, there is rapid communication. The nodes of Ranvier facilitate this rapid communication.

In Lesson 3, you learned that these nodes lack myelin because they are between individual Schwann cells. Here, the axon is in contact with the extracellular fluid. The smooth wave-like nerve impulse that you studied in such detail in the previous sections does not apply to myelinated neurons because action potentials can only occur at the nodes of Ranvier. Scientists found that the neural impulse “jumps” from one node to the next all along the axon in what is called saltatory conduction. For more detail on this process read pages 377 – 378. Figure 11.16 on page 378 provides a good illustration of this process. Add this information to your course folder in a format that you prefer.

Saltatory conduction is like a skillfully thrown rock skipping along a water surface, permitting a greatly increased speed of transmission. The speed of impulses is also increased in axons of large diameter. The fast-reacting giant axons of the squid that allow it to “jet-propel” itself away from danger are several millimeters in diameter, or 100 to 1000 times the diameter of a human axon. However, the squid’s giant axons conduct impulses at only about 30 metres per second which is far below your own capabilities.

Watch and Listen

Multiple Sclerosis

In Lesson 4, you were introduced to the disorder multiple sclerosis (MS), and some of the ways it affects communication in the nervous system.

  Self-Check

MS is a disorder capable of slowing down, or even stopping impulse transmission. Prepare a paragraph, outlining the relationship between myelinated nerve function and the symptoms of MS. Indicate the specific losses of myelinated nerve function caused by MS. After autochecking your answer, put it in your Biology 30 Course Folder for easy access when studying.

1.1.7 page 6

Reflect and Connect

Module 1: Lesson 7 Assignment—Part 3

In previous lessons, you learned about the different parts of the nervous system and nerve transmission pathways. You also learned about sensory receptors that allowed you to hear the mosquito ringtone of a phone. Various lobes of the brain were involved in processing this information, and motor pathways lead to responses. This lesson focused on the neuron, the type of cell that makes up the communication pathways of the nervous system. You discovered the special parts and functions of a neuron, and you considered how these structures facilitated communication and could even accelerate the rate of communication. This leads to an appreciation of the significance of myelination, and an understanding of how symptoms of diseases such as MS indicate interruptions in communication.

Reflect on the Big Picture

In the Big Picture for this module, you were introduced to unconscious and conscious communication in your nervous system. You now know that communication within or between any part of your nervous system involves neurons.

Lesson Summary

In this lesson, you investigated the following focusing question:

• How does the structure of a neuron facilitate reception and transmission of a nerve impulse to the synaptic gap?

To answer this question, you explored the three major parts of nerve impulse transmission through a neuron:

(1)  the resting or polarized state,
(2)  the action potential involving depolarization, and
(3)  the reestablishment of the resting state or repolarization.

You investigated the importance of specific ions in communication. The distribution of the ions in the resting state produces a polarized membrane. In the resting state, the membrane of the neuron is impermeable to Na+ ions. The sodium potassium ion exchange pump uses ATP to pump Na+ ions out of and K+ ions into the neuron. K+ ions diffuse through the selectively permeable membrane, but the negative ions attract them to keep most of the K+ ions inside the neuron. Thus the positive charges dominate outside the neuron and the negative charges dominate the inside of the neuron. This creates the polarized state, with a voltage difference of about -70 mV. Stimulation of a neuron causes depolarization, a shift in ion concentrations and electrical charges. You examined the mechanism of this shift.

When the neuron membrane becomes permeable to Na+ and the Na+ ions flood the inside of the neuron, the voltage difference becomes approximately +40 mV and the permeability to Na+ is lost (sodium gates close). The K+ ions then leave the neuron and the resting potential of -70 mV is restored. The sodium potassium ion exchange pump works to bring the K+ back inside and kicks the Na+ out. This process takes only a millisecond or two and is called the refractory period. The neuron repolarizes in the refractory period and is then ready to be stimulated again. The nerve impulse is passed along the neuron in a wave of depolarization.

In this lesson you also learned that myelinated neurons conduct impulses much more quickly than nonmyelinated neurons because depolarization can only occur at the nodes of Ranvier. Action potentials at the node create enough current flow to activate the sodium gates in the next node so the impulse “jumps” from node to node. Electrical current flow between nodes is instantaneous. Multiple sclerosis is an autoimmune disorder that causes the destruction of the myelin sheath, which ultimately slows down and/or stops the transmission of nerve impulses. This can result in blurred vision, loss of balance, and an inability of muscles to respond to commands from the brain, among other possible symptoms.

Lesson Glossary

action potential: the change in charge that occurs when the gates of the potassium ion channels close and the gates of the sodium ion channels open; a large depolarization event that is conducted along the membrane of a nerve cell or a muscle cell

all or none principle (event): action that occurs either completely or not at all, such as the generation of an action potential by a neuron

depolarization: the loss or reduction of the negative resting membrane potential

hyperpolarization: the process of generating a membrane potential that is more negative than the normal resting membrane potential

membrane potential: a form of potential energy resulting from the separation of charges between the inside and the outside of a cell membrane; voltage across the cell membrane

millivolt: abbreviated as mV, a measure of electricity

myelinated neuron: a neuron whose axon is wrapped by Schwann cells which produce a myelin sheath; these neurons make up the white matter of the brain and the spinal cord and transmit nerve impulses very quickly

overshoot: the situation that results when more potassium ions leak out of the neuron than should because the potassium gates are slow to close; results in hyperpolarization

polarization: the process of generating a resting membrane potential averaging approximately – 70 millivolts

polarized membrane: state of a cell membrane of an unstimulated neuron in which the inside of the neuron is negatively charged in comparison to the outside of the neuron; the resting state of a membrane averaging approximately – 70 millivolts

refractory period: the short time immediately after an action potential in which the neuron cannot respond to another stimulus; period of time it takes to re-establish the net positive charge on the outside of the neuron and the net negative charge on the inside of the neuron, where there are more sodium ions on the outside and more potassium ions on the inside of the neuron

repolarization: restoring the resting membrane potential (- 70 millivolts) from the depolarized state

resting membrane potential: the voltage that exists across a cell membrane during the resting state of an excitable cell such as the neuron; ranges from – 50 to – 200 millivolts (mV) depending on the cell

saltatory conduction: rapid transmission of a nerve impulse along an axon resulting from the action potential jumping from one node of Ranvier to another, skipping the myelinated regions of the membrane

threshold potential: the smallest change in the membrane potential of a cell membrane that is needed to initiate an action potential; approximately 55 millivolts

threshold stimulus: weakest possible stimulus that is needed to initiate a nerve impulse

unmyelinated neuron: a neuron that does not have Schwann cells and therefore lacks a myelin sheath; these neurons make up the grey matter of the brain and spinal cord and transmit nerve impulses much more slowly than myelinated neurons

voltage: electrical potential difference across a membrane as measured by a voltmeter

Lesson 1.1.8

Lesson 8—Synaptic and Neuromuscular Transmission—Crossing the Divide

Get Focused

You hear the most wonderful laughter from across the room. You turn to meet eyes with the most attractive person you have ever seen. All of a sudden, they ask you a question – “do you know the time?” What will you say? You are so nervous! Will a response even come out of your mouth? Thank goodness your nervous system is working and you stutter out the time.

Your Nervous System is responsible for the communication between this person and yourself. Up to this point, you have learned about neurons, and are aware of the tiny gaps between them. Communication usually requires some sort of connection. Think of what happens when the land phone lines are down, or your internet connection goes out. You know what it’s like when there are gaps in your own communication path between the phone and the Iinternet.

So how did the sights and sounds from this attractive person get communicated from neuron to neuron, across the gaps between them? What happens when these “lines go down”?

This lesson is all about the events that occur in the synaptic gap. You will examine how neurons communicate with each other and with muscles. These events can be affected by many substances, such as coffee, energy drinks, alcohol, anesthetics. They can also be affected by disorders such as Parkinson’s Disease and Alzheimer’s Disease.

In this lesson, you will investigate the following focusing questions:

• How does the anatomy and function of the synaptic gap and neuromuscular junction facilitate the transmission of nerve impulses between neurons, and between neurons and effectors?
• How do chemicals that we take into our body and disorders such as Parkinson’s Disease compromise synaptic transmission?

Module 1: Lesson 8 Assignment

Remember that further practice and application can be completed by doing the many questions in the textbook. You can access the answers to these questions from your instructor. The Key will provide you with many Diploma exam style multiple choice, numerical response, and written response questions that will provide excellent review of the module and prove to be good preparation for the Diploma exam.

Once you have completed all of the learning activities for this lesson, you can complete the online assignment.

Bio30 1.1.8 online assignment

Here is a tutorial video for this lesson that you can watch if it suits your learning style.  Bio30 tut#1.1.8

 ** The Self-Check and Try This questions throughout this lesson are not marked by the teacher; however these questions provide you with the practice and feedback that you need to successfully complete this course. **

1.1.8 page 2

Explore

Read

Anatomy of the Synaptic Gap

Your retinal receptor cells registered that attractive person, the olfactory receptors detected the pizza, the pressure receptors were activated by the handshake. The receptor cells converted this information to a nerve impulse and information was on its way through a sensory neuron. But it came to a screeching halt at the end of the sensory neuron. Where to now? How does communication get to the next neuron? In the world of neurons, there’s a big gap to jump to the next neuron. To understand where the transmission goes next and the structures involved in the leap across the gap, study Figure 11.18 on page 379 of your textbook.

Notice that the impulse traveling down the axon reaches the axon ending or synaptic terminal. Recall from your study of the neuron that the tiny enlargement on each axon terminal is called a synaptic knob. Notice the synaptic vesicles in the synaptic knob. These tiny sacs contain chemicals called neurotransmitters which are represented by the little circles.

The synaptic knob is surrounded by the presynaptic membrane. The neuron that ends in the synaptic knob is called the presynaptic neuron. The synaptic cleft is the space between the presynaptic neuron and the next neuron, called the postsynaptic neuron. Remember that the receiving parts of the neuron are called the dendrites. Notice in the diagram that the membrane surrounding the dendrite is called the postsynaptic membrane. Find the sodium ion channels in the postsynaptic membrane. Notice how these channels are only open when the neurotransmitter fits into a receptor.

Crossing the Divide

Have you ever stood on a rock in a stream and struggled with whether or not you could leap to the next rock? You think you can do it: you’re strong and coordinated, but if you fall, your new shoes would get very wet. To understand how a nerve transmission takes the “big leap” across the synaptic gap, study figure 11.18 on page 379, and read pages 378-379.

From the diagram and from your readings you should now know that when the nerve impulse arrives at the synapse it stimulates several reactions that end with the movement of the synaptic vesicles toward the presynaptic membrane and then fusing with it. A neurotransmitter is released into the synaptic cleft and it quickly diffuses across the synapse. Neurotransmitter molecules lock into receptor molecules on the postsynaptic membrane, causing the sodium gates to open and sodium ions from the synaptic cleft rush into the postsynaptic neuron.  You have also already learned that an inflow of sodium ions causes depolarization, and the start of an action potential. This now happens in the postsynaptic neuron (dendrite).

Watch and Listen

To visually explore synaptic transmission,

1. Go to Crash Course - Synapses

As you watch the video, answer the following questions. These questions will be an excellent reference for studying.

1. Outline the reward pathway.
2. What is a synapse?
3. What happens at a synapse during synaptic transmission?
4. What is a synaptic cleft? Is a synaptic cleft different from a synapse?
5. What is a synaptic vesicle?
6. What is the neurotransmitter in the reward pathway?
7. Where are dopamine receptors located?
8. What does the arriving nerve impulse do?
9. What happens to the released neurotransmitter?
10. Why is there a sucking sound in the video?
11. What happens to the dopamine?
12. How is the nerve impulse started in the second neuron?
13. Identify two things that stop nerve impulse transmission.
14. Does one neuron always synapse only with one other neuron? Suggest where this might be true.

1.1.8 page 3

Reabsorption of Neurotransmitters

Why don’t neurotransmitters continue to start new nerve impulses over and over again? This normally does not happen because the neurotransmitter is transported back into the presynaptic neuron, or it is broken down by enzymes and the fragments are moved back into the synaptic knob. For example, if the neurotransmitter is acetylcholine, then the enzyme cholinesterase breaks it down and the fragments are reabsorbed into the synaptic knob. Scientists have created insecticides that bind up cholinesterase causing acetylcholine to stay in the synapse and continually stimulate the muscles until they become fatigued and no longer contract. The insect dies because it can no longer contract muscles to get oxygen into its body. If the neurotransmitter is norepinephrine, then it is reabsorbed directly into the presynaptic neuron. You can review what happens to the neurotransmitter by reading pages 380 and 381.

Self-Check

To ensure that you understand the events that occur in synaptic transmission answer the following questions. If you do not understand any part of synaptic transmission, you should contact your instructor. Remember to phrase your answers in complete sentences using correct biological terminology. Consult the key for examples. Discuss any questions or concerns with your instructor. File your completed answers in your course folder.

1. Summarize the events involved in impulse transmission starting at the presynaptic neuron and ending at postsynaptic neuron.

2. Identify the function of neurotransmitters in the nervous system.

3. Place the following events in the correct sequence:

1. an action potential is initiated in the dendrite
2. neurotransmitters are released into the synaptic cleft
3. sodium gates are opened and sodium ions rush into the dendrite
4. a wave of depolarization arrives at the axon terminal

4. Deadly neurotoxins produced by some organisms, such as the rattlesnake and black widow spider, could have medical implications. One neurotoxin found in rattlesnake venom blocks receptors on postsynaptic neurons. Venom from the female black widow spider stimulates exocytosis of synaptic vesicles from neurons. Speculate how these neurotoxins might affect the body, and suggest a possible medical use for each of them.

5. Explain what happens to the neurotransmitters once an action potential has been started in the postsynaptic neuron.

1.1.8 page 4

Neuromuscular Junctions

Now you know how messages are communicated from neuron to neuron through the nervous system. However, when you try to talk, how do the muscles in your mouth “get the message” from the neurons?

Read

To understand how muscles and neurons communicate read pages 380 – 382, which detail the events that occur at the tiny gap located between the axon terminal and the muscle cell. Once you have done the reading, you should choose to do one of the following:

make summary notes for your course folder

OR

prepare a fully labeled diagram which outlines the process that occurs at the synaptic gap

OR

prepare a flow chart that outlines the events at the synaptic gap

Make sure that your work addresses the following questions:

• What causes the synaptic vesicles to move toward the presynaptic membrane and fuse with it? 
• What does the neurotransmitter that is released do? 
• What does the fusion of the neurotransmitter, in this case the chemical acetylcholine, with the protein receptor do?
• What event does this initiate?

Please note that the figure incorrectly labels the sarcolemma as the neural membrane, when in fact the sarcolemma is a muscle cell membrane.

Try This

Interruption of neuromuscular transmission can have deadly effects on the body, particularly if the breathing muscles such as the diaphragm are affected. Research the following neurotoxins that act directly on neuromuscular junctions.

1. The native tribes of South America apply a plant extract called curare to the tips of their arrows. Research how curare specifically affects neuromuscular junctions and why it is such an effective poison for the tribesmen.
2. Botulism is a dreaded food poisoning that can be contracted by eating improperly canned foods. The neurotoxin involved in botulism is also the main ingredient in wrinkle reduction injections called Botox. Research botulism to discover how the toxin specifically affects neuromuscular junctions. What is the result of this toxin on the body? Is there an antidote? How does botulism, in the form of Botox injections, reduce wrinkles?

1.1.8 page 5

A Closer Look at Neurotransmitters

When you saw that attractive person with the beautiful eyes across the room, something made you want to get moving across the room, but at the same time, something held you back. Neurotransmitters can be somewhat like that too. They are either excitatory or inhibitory at the synapse or at the neuromuscular junction. Sometimes the same neurotransmitter may be both inhibitory and excitatory!

Read

To find out how neurotransmitters work read pages 379 – 380 of your text.

By opening potassium channels or chloride channels in the postsynaptic membrane, inhibitory neurotransmitters make it harder to initiate depolarization in the second neuron because the neuron develops a much lower membrane potential. Just like opening the windows on a winter day and letting the heat out, it is harder to warm the room up. Excitatory neurotransmitters open up sodium channels and make it easier to start depolarization because the membrane potential becomes less negative. Putting an electric heater into the room makes it easier to warm up the room. Acetylcholine and norepinephrine are excitatory neurotransmitters.

Acetylcholine is a common neurotransmitter in the somatic nervous system, and it is also found between the parasympathetic neurons of the autonomic nervous system. It is also found in some synapses of the brain. Norepinephrine (also called noradrenalin) is an important neurotransmitter in the sympathetic nervous system, and is also found in some synapses in the brain. Review pp.378 – 382 in your textbook and study the table below to learn more about some important neurotransmitters and their characteristics.

Characteristics of Selected Neurotransmitters

Try This

Using your textbook, the Internet, and any other sources that may be available to you, research what happens in the body when acetylcholine, norepinephrine, dopamine, serotonin, glutamate, GABA, or endorphins are not produced in appropriate amounts in the body. Add this new information to the table above.

OR

You may choose to do Questions 6, 7, 8 on page 384 of the text. Check your answers with your teacher.

Try This

The inability of the body to produce appropriate amounts of a neurotransmitter can result in serious consequences for the body. Michael J. Fox and Mohammed Ali are two famous people who have been afflicted with Parkinson’s Disease.  This disease seriously interrupts communication in the nervous system. Research the following questions on Parkinson’s Disease. Post your research on the discussion board or build a wiki with a group of students. If you are building a wiki, you can split up the questions for different group members to complete.  Make any modifications to your work, discuss your research with your instructor, and file your research in your course folder.

• Define Parkinson’s Disease.

• List the symptoms that are associated with Parkinson’s Disease and explain these symptoms based on your understanding of this lesson.

• Outline the causes of Parkinson’s Disease.

• Describe 2 possible treatments for someone with Parkinson’s Disease.

• Briefly explain what a stem cell is, and how it can be used to treat Parkinson’s disease.

Outline the societal and technological issues associated with using embryonic stem cell transplants to treat Parkinson’s Disease.

Self-Check

Check your understanding of the concept of neurotransmitters by answering the following questions in full sentences. If at any point you require more help, consult with your instructor.

1. Compare the effects of excitatory and inhibitory neurotransmitters on the postsynaptic membrane.
2. Explain the relationship between acetylcholine and cholinesterase.
3. Parkinson’s Disease is associated with which neurotransmitter? Identify which area of the brain is affected by this disease and the evident symptom that results.

1.1.8 page 6

The Effect of Drugs on Neurons and Synapses

A drug is a substance that changes the way the body functions. Most drugs, whether they are legal or illegal, affect the neural synapses by either enhancing or decreasing the action of a neurotransmitter. They do this by affecting the vesicles, the receptor proteins, the ion gates in the postsynaptic membrane or the re-absorption of neurotransmitters.

Read

To understand how drugs interrupt communication, read page 383 of your text.

Try This

Explore one of the following:

• Drugs of Abuse
• Physiology of a High
• Hardwiring an Addict
• Changes Last Long after Use
• How PET Scans can Measure Brain Activity
• Death by Overdose

Self-Check

Synaptic and neuromuscular transmitters are important and often challenging concepts to master. To ensure your understanding, you should do the following self check.

Use the following information to answer the next two questions.

Opiate Drugs

The human body naturally produces its own opiate-like substances and uses them as neurotransmitters. These substances include endorphins, enkephalins, and dynorphin, often collectively known as endogenous opioids. Endogenous opioids modulate our reactions to painful stimuli. They also regulate vital functions such as hunger and thirst and are involved in mood control, immune response and other processes.

The reason that opiates such as heroin and morphine affect animals so powerfully is that these exogenous substances bind to the same receptors as our endogenous opioids. There are three kinds of receptors widely distributed throughout the brain: mu, delta, and kappa receptors.

These receptors, through secondary messengers, influence the likelihood that ion channels will open, which in certain cases reduces the excitability of neurons.  This reduced excitability is likely the source of the euphoric effect of opiates, and appears to be mediated by the mu and delta receptors.

This euphoric effect also appears to involve another mechanism in which the GABA (gamma aminobutyric acid) inhibitory interneurons of the ventral tegmental area come into play. By attaching to their mu receptors, exogenous opioids reduce the amount of GABA released. Normally, GABA reduces the amount of dopamine released in the nucleus accumbens in the brain. By inhibiting the effects of this inhibitor, the opiates ultimately increase the amount of dopamine produced and the amount of pleasure experienced.

Source:  The Brain from Top to Bottom: http://www.thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_heroine.html#drogues

1.  The two receptors thought to be involved in the euphoric effects of opiate drugs are

1. mu and delta
2. exogenous and endogenous
3. dopamine and GABA
4. endorphins and enkephalins

2.   Which of the following naturally occurring substances regulate hunger and thirst?

1. mu, delta, and kappa receptors
2. exogenous opioids
3. endogenous opioids
4. dopamine

Use the following information to answer the next two questions.

Avoiding a Collision

You are driving down a highway at night when a deer jumps in front of your vehicle. You slam on the brakes and avoid a collision.

3. Which row below best describes the initial reaction of your autonomic nervous system to this situation?
   
   

   Row	System Involved	Neurotransmitter	Response
   a.	Sympathetic Nervous System	Norepinephrine	Heart rate increases; pupils of eyes dilate
   b.	Parasympathetic Nervous System	Acetylcholine	Heart rate increases; pupils of eyes dilate
   c.	Sympathetic Nervous System	Acetylcholine	Heart rate increases; pupils of eyes constrict
   d.	Parasympathetic Nervous System	Norepinephrine	Heart rate decreases; pupils of eyes constrict

   
   
   
4. Which row below best describes the reaction of your autonomic nervous system several minutes after the incident?
   
   

   Row	System Involved	Neurotransmitter	Response
   a.	Sympathetic Nervous System	Norepinephrine	Heart rate increases; pupils of eyes dilate
   b.	Parasympathetic Nervous System	Norepinephrine	Heart rate increases; pupils of eyes dilate
   c.	Sympathetic Nervous System	Acetylcholine	Heart rate decreases; pupils of eyes constrict
   d.	Parasympathetic Nervous System	Acetylcholine	Heart rate decreases; pupils of eyes constrict

Use the following information to answer the next question.

5. Destruction of the synaptic vesicles of Neuron 1 will
   
   
   1. block the nerve impulse at W
   2. cause X to be constantly stimulated
   3. prevent depolarizations from occurring at Y
   4. result in the action of cholinesterase in Neuron 2

Use the following information to answer the next question.

6. If the structures labeled Q were absent, what effect on neural transmission would be expected?
   
   
   1. The axon would not release acetylcholine.
   2. The axon would not become depolarized.
   3. The speed of transmission would be reduced.
   4. No action potential would arrive to release neurotransmitter.

Use the following information to answer the next question.

The disease myasthenia gravis causes a person to experience muscular weakness because of the failure of neuromuscular junctions to transmit signals from nerve fibres to muscle fibres. The weakness is due to a reduced sensitivity to acetylcholine, which is necessary to stimulate the muscle fibre. People suffering from this disease are often treated with neostigmine, an anticholinesterase drug, which can result in some normal muscular activity within minutes.—Guyton and Hall, 1996

7. Neostigmine is effective in treating this disease because it
   
   
   1. binds with cholinesterase to form acetylcholine
   2. binds with cholinesterase to increase acetylcholine production
   3. reduces the amount of active cholinesterase, thereby increasing the amount of acetylcholine available to stimulate muscle contraction
   4. increases the amount of active cholinesterase, thereby increasing the amount of acetylcholine available to stimulate muscle contraction

Use the following information to answer the next question.

Observations About a Synapse and Synaptic Transmission

1. Only axon terminals release neurotransmitters.
2. A neurotransmitter diffuses from an axon terminal across the synapse to the dendrites or cell body.
3. Many transmissions across a synapse in a short time may cause fatigue of synaptic transmission.
4. Electron micrographs of a synapse show that there is no direct connection between the axon terminal of a presynaptic neuron and the dendrites or cell body of a postsynaptic neuron.

8. The assumption that axon terminals contain a limited amount of neurotransmitter could account for observation
   
   
   1. 1
   2. 2
   3. 3
   4. 4

Use the following information to answer the next question.

Alternative medicine, such as aromatherapy, is becoming increasingly popular in western society.  Aromatherapy uses natural oils and plant extracts. The scents of the oils and extracts are inhaled or the fragrant oils are massaged into the skin. Proponents of aromatherapy hypothesize that odours affect the brain and its release of neurochemicals. These neurochemicals may then relieve pain.

Hypothesized Steps in Aromatherapy Action

1. Olfactory neurons depolarize.
2. Olfactory receptors are stimulated.
3. Neurochemicals affect pain interpretation.
4. Neurochemicals are released from axon terminals.

Numerical Response

9. If it is assumed that the hypothesis is correct, the order in which the steps above would occur to result in pain relief in a person having just inhaled the scent from an aromatherapy oil or extract is ______, ______, ______, and ______.

10. While working in a lab, you accidentally mixed some unknown chemicals together and a vapour was produced which diffused throughout the lab.  Soon the lab animals in the room collapsed, unable to move. You made a quick examination of the animals and found their musculature to be very loose and relaxed. You concluded that the vapour became internalized in the animals by way of the lungs to the blood, which then distributed the vapour throughout the animals’ bodies. The symptoms shown by the lab animals may lead you to conclude that the vapour could have
    
    
    1. stimulated the action of the enzyme cholinesterase
    2. inhibited the production of acetylcholine by the axon endings of neurons
    3. inhibited the formation of synaptic transmission chemical produced by the dendrites
    4. stimulated the axon endings to secrete large amounts of acetylcholine

1.1.8 page 7

Reflect and Connect

Reflect on the Big Picture

From the Big Picture scenario, your rapidly beating heart, your increased breathing rate, and the simple walking across the room take on a whole new meaning. In this lesson, you have examined how the information communicated through neurons can then be transmitted across the gap between neurons, or between a neuron and a muscle. You have examined the various types of neurotransmitter substances found naturally in the body, and you should now understand how they can speed up or slow down communication. You have also looked at the effect of drugs on the synaptic gap.

Lesson Summary

In this lesson, you have explored the following focusing questions:

• How does the anatomy and function of the synaptic gap and neuromuscular junction facilitate the transmission of nerve impulses between neurons, and between neurons and effectors?
• How do chemicals that we take into our body and disorders such as Parkinson’s Disease compromise synaptic transmission?

The parts of the nervous system: neurons, neural pathways, receptors, effectors and synapses all fir together like the pieces of a puzzle. If one piece fails to fit, the system doesn’t work right. Disorders such as Parkinson’s Disease and chemical substances such as drugs can interrupt the function of the system.

Glossary

acetylcholine: one of the most common neurotransmitters of both the somatic nervous system and the parasympathetic nervous system; functions by binding to receptors on the postsynaptic membrane and either depolarizing or hyperpolarizing the membrane

cholinesterase: an enzyme necessary to decompose acetylcholine in the synaptic cleft so that the products (choline and ethanoic acid) can be reabsorbed by the presynaptic membrane; also called acetylcholinesterase

dopamine: generally an excitatory neurotransmitter in the CNS

excitatory neurotransmitter: neurotransmitters that promote nerve impulse transmission in the postsynaptic membrane by opening sodium channels

GABA (gamma aminobutyric acid): an inhibitory neurotransmitter in the CNS

glutamate: an excitatory neurotransmitter in the CNS

inhibitory neurotransmitter: neurotransmitters that hinder nerve impulse transmission in the postsynaptic neuron by hyperpolarizing it

neuromuscular junction: tiny gap located between an axon terminal and a muscle cell

neurotransmitters: chemical messengers released from the synaptic knob of a neuron at a synapse that diffuse across the synaptic cleft, bind to specially shaped protein receptors on the postsynaptic membrane, and stimulate the postsynaptic neuron

norepinephrine: neurotransmitter released by sympathetic neurons of the autonomic system to produce an excitatory effect on target muscles; also called noradrenalin

postsynaptic neuron: the receiving neuron

postsynaptic membrane: the cell membrane of the cell body, or  the dendrite on the other side of the synapse

presynaptic neuron: the sending neuron

presynaptic membrane: the surface membrane surrounding the synaptic knob and facing the synaptic cleft

receptor proteins: protein molecules located on the postsynaptic membrane that have complementary shapes to certain neurotransmitters, allowing the neurotransmitter to fit into them

serotonin: an inhibitory neurotransmitter in the CNS

synapse: the location or junction in a neural pathway where one neuron communicates with another neuron; a tiny gap between the synaptic terminal of an axon and the signal receiving dendrite or cell body of another neuron or an effector, such as a muscle

synaptic cleft: a tiny space separating the synaptic knob of a transmitting neuron from a receiving neuron or effector cell

synaptic knob: the tiny enlarged ending on an axon terminal

vesicles: tiny membranous sacs that, in this case, contain neurotransmitters; also called synaptic vesicles

Module Summary

Module Summary

In this module, you studied the nervous system and how it communicates to maintain homeostasis in the body. You investigated how various sense cells/organs help you to see a person, notice their smile, and hear their laughter from across the room. You explored how these sensations were transmitted electrochemically between neurons to specific areas of the brain so that they could be interpreted. Your discovered how your brain was able to send nerve impulses to your leg muscles so that you could walk in the direction of the person of interest. These communications were conscious. Other parts of the brain, such as the medulla oblongata, sent out unconscious messages via the sympathetic nervous system that altered your heart rate and caused your hands to become clammy. After that initial “hello”, your parasympathetic nervous system slowed the heart down and returned your body to homeostasis. You investigated how several disorders, such as multiple sclerosis, Alzheimer’s Disease, and Parkinson’s disorder disrupt communication in the nervous system, cause a loss of homeostasis, and require corrective technologies to attempt to bring the system back to homeostasis.

In this module you should have completed the following assignments Bio30 1.1.1 - Bio 1.1.8.

You should have also submitted tutorial summaries for tutorial videos 1.1.1 - 1.1.8 (Eight in total)

If the above is complete, you can now write the Nervous System Exam or the Nervous System Exam IPP .  Your key contact should send a password request.