Module 1 Lesson 5 - 2
Completion requirements
Lesson 5 — The Basic Units of the Nervous System: The Neuron and the Reflex Arc
The Neuron
Read pages 368 - 384
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A neuron is the basic cell of the nervous system. Neurons carry signals through electrochemical processes called action potentials. Neurons are grouped into bundles and multiple nerve bundles are organized into nerve fibres.
The dendrites of a cell body receive signals from other neurons. The cell body carries out the life functions of the nerve cell. The axon takes the signal away from the cell body for transmission. The signal travels along the axon until it reaches the end, the axon terminal.
Sensory (afferent) neurons receive nerve impulses from the sensory receptors to the interneurons. Interneurons in the central nervous system enable communication between sensory or motor neurons and the central nervous system (CNS). Motor (efferent) neurons communicate nerve impulses rapidly away from the central nervous system to effectors (muscles).
Neurons are surrounded and supported by protective cells called glial cells. One type of glial cells is the Schwann cells, which produce a fatty material called myelin sheath that insulates the axon and increases the speed of nerve impulse transmission.
The dendrites of a cell body receive signals from other neurons. The cell body carries out the life functions of the nerve cell. The axon takes the signal away from the cell body for transmission. The signal travels along the axon until it reaches the end, the axon terminal.
Sensory (afferent) neurons receive nerve impulses from the sensory receptors to the interneurons. Interneurons in the central nervous system enable communication between sensory or motor neurons and the central nervous system (CNS). Motor (efferent) neurons communicate nerve impulses rapidly away from the central nervous system to effectors (muscles).
Neurons are surrounded and supported by protective cells called glial cells. One type of glial cells is the Schwann cells, which produce a fatty material called myelin sheath that insulates the axon and increases the speed of nerve impulse transmission.
The myelinated neurons form the white matter in the central nervous system, and the unmyelinated neurons form the grey matter. Most of the neurons in the peripheral nervous system are myelinated.
The gaps between the myelin sheathes are called the nodes of Ranvier. The nerve impulses travelling along the myelinated axon ‘jump’ from node to node, thereby increasing the speed of nerve impulse transmission. The axon terminals have many bulbous knobs that produce neurotransmitters.
Lesson 7 explains how neurotransmitters complete communication between neurons. These neurotransmitters are necessary because neurons are not joined physically. Neurotransmitters take more time to diffuse across synapses than nerve impulses take to travel along the axons.
The gaps between the myelin sheathes are called the nodes of Ranvier. The nerve impulses travelling along the myelinated axon ‘jump’ from node to node, thereby increasing the speed of nerve impulse transmission. The axon terminals have many bulbous knobs that produce neurotransmitters.
Lesson 7 explains how neurotransmitters complete communication between neurons. These neurotransmitters are necessary because neurons are not joined physically. Neurotransmitters take more time to diffuse across synapses than nerve impulses take to travel along the axons.
Watch and Listen
To review the structures of the neuron, watch this biosimulation of the neuron.
©Alberta Education. Electrochemical Control Systems in Humans: Regulating Physiological Processes (11:29 - 13:19); BiologiX Series 01. LearnAlberta.ca
Self-Check
Inquiry into Biology
(Whitby, ON: McGraw-Hill Ryerson, 2007), 372, fig. 11.9. Reproduced by permission.
Identify and write the name of the correct structure in the space. Match the following functions to their respective structures indicated on the image below.
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
- 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
- Type of supporting nerve cell that wraps around axons in the peripheral nervous system and produces myelin
Self-Check Answers
- cell body: performs life functions and relays messages to the axon
- nucleus: control centre of the cell
- dendrites: receive input from other neurons of sensory receptors and transmit toward the cell body
- myelin sheath: fatty insulating layer that increases rate of communication transmission
- nodes of Ranvier: gaps in myelin sheath that increase rate of communication transmission
- axon: transmits nerve impulses away from cell body
- Schwann cell: type of supporting nerve cell that wraps around axons in the peripheral nervous system and produces myelin