1. Module 1

1.14. Page 2

Lesson 3

Module 1—The Nervous System

Explore

 

In Lesson 1 you learned about 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.

 

In Lesson 3 you will learn about the structures and functions of the neuron, the basic cell of the nervous system.

 

Read

 

To help you understand neurons, read “The Structure of a Neuron” on pages 370 and 372 in your textbook. You may wish to make summary notes and save them in your course folder for future study. It is important to include a labelled diagram of a neuron similar to “Figure 11.9” on page 372 of your textbook.

 

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

 

axon: the long extension that emerges from the cell body and conducts the nerve impulse away from the cell body

 

The axon may be up to 1 m long in motor neurons.

 

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

 

myelin sheath: a fatty insulating layer that surrounds axons and greatly increases the rate of impulse transmission and maintains the strength of the impulse by preventing the loss of ions along the length of the axon

 

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.

 

axon terminal: numerous endings found at the end of an axon

 

Axon terminals are enlarged into knobs that are specialized for producing, storing, and releasing neurotransmitters.

You are now familiar with the dendrites, the parts of the nerve that receive impulses; the cell body, which carries out the life functions of the nerve cell; and the axon, which takes nerve impulses away from the cell.

 

Motor neurons communicate nerve impulses rapidly to effectors. Motor neurons are myelinated, which means their axons are surrounded by Schwann cells. Schwann cells produce a fatty material called the myelin sheath, which insulates the axon. This insulation prevents the loss of ions into the extracellular environment. You will learn about these ions and their role later in the module.

 

You will also learn how the nodes of Ranvier help to increase the transmission speed of nerve impulses and how the axon terminals produce neurotransmitters that complete communication between neurons. These neurotransmitters are necessary because neurons are not physically joined together. It is important to understand the basic structure and the function of the neuron in this lesson to help you master these more complex concepts.

 

In the nervous system, there are no physical connections between neurons to facilitate the transmission of an impulse. In electricity, the connections must be physically complete for the communication, or flow, of electricity to occur.

 

This illustration shows the structures of the neuron, including the cell body, nucleus, dendrites, axons, Schwann cell, node of Ranvier, and myelin sheath.

 

Adapted from  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, watch “Bio Reports: Neuron Structure and Function” in the video “Electrochemical Control Systems in Humans: Regulating Physiological Processes.”

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. Complete the matching worksheet to show your understanding of the function and structure of neurons.

 

Check your work.
Self-Check Answers

 

SC 1.

 

Structure 1
Name: cell body
Function: performs life functions, relays messages to the axon

Structure 2
Name: nucleus
Function: control centre of the cell

Structure 3
Name: dendrites
Function: receive input from other neurons of sensory receptors and transmit toward the cell body

Structure 4
Name: myelin sheath
Function: fatty insulating layer that increases rate of communication transmission

Structure 5
Name: node of Ranvier
Function: gaps in myelin sheath that increase rate of communication transmission

Structure 6
Name: axon
Function: transmits nerve impulses away from cell body

Structure 7
Name: Schwann cell

Function: a type of supporting nerve cell that wraps around axons in the peripheral nervous system and produces myelin

 

Try This

 

Check whether you can correctly assemble a neuron from a mad scientist’s tray of parts.