Module 1 The Nervous System
Lesson 1.1.3
Lesson 3—The Basic Units of the Nervous System: The Neuron and the Reflex Arc
Get Focused
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
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
sensory neuron: a type of nerve cell that receives stimuli and conducts an impulse toward the brain and spinal cord (central nervous system)
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
effector: one of the three types of muscle or a gland that responds to a nerve impulse
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
** 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. **