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3.
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Chapter 8: Function of the Nervous System
Completion
1. neurons, neuroglia
6.
7.
8. nerve cell body, dendrite, axon, terminus dendrites, axons, axoaxonic synapse presynaptic, postsynaptic bipolar, multipolar, unipolar blood-brain barrier, cerebrospinal fluid resting potential, action potential, depolarization excitatory, inhibitory
9. affector, effector
10. congenital, toxicological, traumatic d. e. f. g.
Matching a. genetic degenerative disorder b. c. excitatory neurotransmitter maintain cell health and activity inhibitory amino-acid neurotransmitter more negative potential than resting potential cell secretions used to communicate information bipolar neuron dendrites h. i. j. k. indicates nerve cell pathology capable of invading neurons to travel across produce myelin l. nerve cell body m. gap at the nerve terminus n. o. point of sodium channel opening site of neurotransmitter release
Key Terms Table
Key Term external stimuli
neural tube axon hillock dendrites satellite cells
Definition environmental factors that influence metabolic changes in a cell, or physiological changes in tissues and organs ectoderm tissue in the fetal back that produce stem cells that form nerve tissue cells the region of the nerve cell body from which the axon extends neuron cell extensions that receive stimuli
neuroglial cells that help to maintain the chemical environment of neurons and may help in nerve cell repair

nodes of Ranvier refractory period tetany dopamine innervate reverberating pathway reflexes meningitis bovine spongiform encephalopathy
(mad cow disease) tonic control gaps between the myelin sheaths of the axon that are responsible for carrying stimuli along the axon’s length the action-potential stage following repolarization during which a normal stimulation will not cause another action potential continuous cell excitation with little or no recovery a catecholamine neurotransmitter that can be inhibitory as well as excitatory to supply a body part with nervous stimulation a type of neuron-arrangement pathway in which neurons are capable of stimulating themselves over and over again until another stimulus comes along to stop the stimulation involuntary responses to a stimulus inflammation of the membranes surrounding the brain a neurotrophic disease that is caused by infectious prions that can be contracted through exposure to the blood and meat of infected animals a slight tension in muscles produced by small, continuous impulses to certain glands and almost all muscles
Label the Graphic: See the PDF in the Chapter 08 folder on the Instructor’s CD.
1. motor neuron = multipolar sensory neuron = unipolar
2. interneuron = bipolar
1) sensory; 2) interneuron; and 3) motor neuron
Color the Graphic: A color-coded answer key is available on the Instructor’s Guide
CD accompanying this text.
1. Central nervous system: 1) the presence of oligodendrites, rather than Schwann cells, forming the myelin sheaths; and 2) the presence of ependymal cells, which form CSF.
Practical Application Questions
1. A sensory, or afferent, neuron would most likely be unipolar. It would send the stimulus from the receptor cell to the second neuron portion of the arc, the interneuron. Interneurons are called bipolar by shape. The third and final neuron

2.
3.
4.
5.
6.
7.
8. in a reflex arc is the efferent, or motor, neuron, which is usually a multipolar neuron as classified by shape.
The same neurotransmitter can produce an excitatory postsynaptic potential at one synapse, but it can cause the opposite, inhibitory, postsynaptic potential if it is acting at a different synapse. The direction of the effect depends on the type of target cell. Receptors on certain target cells might open a particular ion channel
(when stimulated by a neurotransmitter) that will result in excitability. Binding of the same neurotransmitter to the same receptor located on a different type of target cell may alter the target cell's metabolism such that it will inhibit the impulse. Therefore, the response depends on the type of target cell, not the type of receptor located on it.
No. Neurotransmitters are always released from the terminus of the presynaptic neuron of the synapse. The receptor sites are located on the postsynaptic neuron.
Therefore, action potentials can only move in one direction from the presynaptic side of the synaptic cleft to its postsynaptic side.
Depolarization refers to a decrease in the membrane potential from resting potential. At this stage of the action potential, the cell's interior is moving from the more-negative resting potential to a more-positive measurement. This occurs because sodium channels have opened, allowing these positively charged sodium ions to enter the cell. Therefore, the membrane potential is decreasing during depolarization. Repolarization is a return to resting potential following depolarization; it increases membrane potential from the decreased depolarization of membrane potential. The reversal occurs from sodium channels closing and potassium channels opening, which causes an efflux of positively charged potassium ions from the cell's interior to the outside. Therefore, the cell's interior is once again becoming more negative. Hyperpolarization refers to an increased membrane potential compared with resting potential. It occurs briefly following the loss of positively charged potassium ions until the sodium/potassium pump returns the cell to resting potential.
Decrease. The postsynaptic side would have to involve the receptor. The drug would most likely have the ability to occupy the receptor without inducing a metabolic change in the target cell. In essence, it would be blocking just the ability of the neurotransmitter to bind to the receptors.
Microglial cells are phagocytic cells that help to fight off invading organisms.
Therefore, their presence in high numbers might indicate a neurotrophic disease.
The similarity between these two types of microglial cells is their function to produce the myelin sheaths covering axons. The difference between them is their location; oligodendrites function only in the central nervous system (brain and spinal cord), while Schwann cells produce myelin on axons of peripheral nerves.
Glutamate is an excitatory amino-acid neurotransmitter. A lack of it would decrease, not increase, excitatory activity. Therefore, it would be a lack of GABA

because it is an inhibitory amino-acid neurotransmitter. Without inhibitory input, excitatory neuronal activity could become uncontrolled.
9. If the loss of innervation is severe enough, victims of this disease would lose the ability to breath, as contraction of these muscles allows for expansion of the rib cage and the subsequent movement of air into the lungs. Death would eventually occur from respiratory failure.
10. Neurons are not capable of mitosis. Therefore, they are subject to the accumulated effects of damage over their lifespan without the possibility of replication to replace damaged neurons. Second, they have a very high metabolic rate compared with many cells in the body. Consequently, they produce more waste products from these chemical reactions, which may cause adverse effects. Their high metabolic rate also gives them a higher demand for nutrients than many body cells. Diminished blood flow, which commonly accompanies aging, may be inadequate in supplying this need.
12. b
13. c
14. a
15. d
16. b
17. d
18. a
19. d
20. d
21. d
22. a
23. b
24. d
25. a
Crossword Puzzle: A completed puzzle is available in the Chapter 08 folder on the
Instructor’s CD.
Quiz
1. False
2. b
3. c
4. c
5. b
6. c
7. a
8. d
9. d
10. b
11. d