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Test Your Knowledge ofTerms and Facts

1. The supporting cells that form myelin sheaths in the peripheral nervous system are a. oligodendrocytes.

b. satellite cells.

c. Schwann cells.

d. astrocytes.

e. microglia.

2. A collection of neuron cell bodies located outside the CNS is called a. a tract.

d. a ganglion.

3. Which of these neurons are pseudounipolar?

a. sensory neurons b. somatic motor neurons c. neurons in the retina d. autonomic motor neurons

4. Depolarization of an axon is produced by a. inward diffusion of Na+.

b. active extrusion of K+.

c. outward diffusion of K+.

d. inward active transport of Na+.

5. Repolarization of an axon during an action potential is produced by a. inward diffusion of Na+.

b. active extrusion of K+.

c. outward diffusion of K+.

d. inward active transport of Na+. As the strength of a depolarizing stimulus to an axon is increased, a. the amplitude of action potentials increases.

b. the duration of action potentials increases.

c. the speed with which action potentials are conducted increases.

d. the frequency with which action potentials are produced increases.

The conduction of action potentials in a myelinated nerve fiber is a. saltatory.

b. without decrement.

c. faster than in an unmyelinated fiber.

d. all of the these.

Which of these is not a characteristic of synaptic potentials?

a. They are all or none in amplitude.

b. They decrease in amplitude with distance.

c. They are produced in dendrites and cell bodies.

d. They are graded in amplitude.

e. They are produced by chemically regulated gates.

9. Which of these is not a characteristic of action potentials?

a. They are produced by voltage-regulated gates.

b. They are conducted without decrement.

d. The membrane potential reverses polarity during depolarization.

10. A drug that inactivates acetylcholinesterase a. inhibits the release of ACh from presynaptic endings.

b. inhibits the attachment of ACh to its receptor protein.

c. increases the ability of ACh to stimulate muscle contraction.

d. does all of the these.

11. Postsynaptic inhibition is produced by a. depolarization of the postsynaptic membrane.

b. hyperpolarization of the postsynaptic membrane.

c. axoaxonic synapses.

d. long-term potentiation.

12. Hyperpolarization of the postsynaptic membrane in response to glycine or GABA is produced by the opening of a. Na+ channels.

c. Ca2+ channels.

13. The absolute refractory period of a neuron a. is due to the high negative polarity of the inside of the neuron.

b. occurs only during the repolarization phase.

c. occurs only during the depolarization phase.

d. occurs during depolarization and the first part of the repolarization phase.

14. Which of these statements about catecholamines is false?

a. They include norepinephrine, epinephrine, and dopamine.

b. Their effects are increased by action of the enzyme catechol-O-methyltransferase.

c. They are inactivated by monoamine oxidase.

d. They are inactivated by reuptake into the presynaptic axon.

e. They may stimulate the production of cyclic AMP in the postsynaptic axon.

15. The summation of EPSPs from numerous presynaptic nerve fibers converging onto one postsynaptic neuron is called a. spatial summation.

b. long-term potentiation.

c. temporal summation.

d. synaptic plasticity.

16. Which of these statements about ACh receptors is false?

a. Skeletal muscles contain nicotinic ACh receptors.

b. The heart contains muscarinic ACh receptors.

Test Your Understanding of Concepts and Principles

1. Compare the characteristics of action potentials with those of synaptic potentials.1

2. Explain how voltage-regulated channels produce an all-or-none action potential.

3. Explain how action potentials are regenerated along an axon.

4. Explain why conduction in a myelinated axon is faster than in an unmyelinated axon.

5. Describe the structure of nicotinic ACh receptors. Explain how ACh causes the production of an EPSP and relate this process to the neural stimulation of skeletal muscle contraction.

6. Describe the nature of muscarinic ACh receptors and the function of G-proteins in the action of these receptors. How does stimulation of these receptors cause the production of a hyperpolarization or a depolarization?

7. Trace the course of events in the interval between the production of an EPSP and the generation of action potentials at the axon hillock. Describe

TestYour Ability to Analyze and Apply Your Knowledge

1. Grafting peripheral nerves onto the two parts of a cut spinal cord in rats was found to restore some function in the hind limbs. Apparently, when the white matter of the peripheral nerve was joined to the gray matter of the spinal cord, some regeneration of central neurons occurred across the two spinal cord sections. What component of the peripheral nerve probably contributed to the regeneration? Discuss the factors that promote and inhibit central neuron regeneration.

Discuss the different states of a voltage-gated ion channel and distinguish between these states. How has molecular biology/biochemistry c. G-proteins are needed to open ion channels for nicotinic receptors.

d. Stimulation of nicotinic receptors results in the production of EPSPs.

17. Hyperpolarization is caused by all of these neurotransmitters except a. glutamic acid in the CNS.

b. ACh in the heart.

c. glycine in the spinal cord.

d. GABA in the brain.

18. Which of these may be produced by the action of nitric oxide?

a. dilation of blood vessels b. erection of the penis c. relaxation of smooth muscles in the digestive tract d. long-term potentiation (LTP) among neighboring synapses in the brain e. all of the these the effect of spatial and temporal summation on this process.

8. Explain how an IPSP is produced and how IPSPs can inhibit activity of the postsynaptic neuron.

9. List the endogenous opioids in the brain and describe some of their proposed functions.

10. Explain what is meant by long-term potentiation and discuss the significance of this process. What may account for LTP and what role might nitric oxide play?

aided our understanding of the physiology of the voltage-gated channels?

3. Suppose you are provided with an isolated nerve-muscle preparation in order to study synaptic transmission. In one of your experiments, you give this preparation a drug that blocks voltage-regulated Ca+ channels; in another, you

1Note: This question is answered in the chapter 7 Study Guide found on the Online Learning Center at www.mhhe.com/fox8.

The Nervous System: Neurons and Synapses 187

give tetanus toxin to the preparation. How will synaptic transmission be affected in each experiment? 4. What functions do G-proteins serve in 5. synaptic transmission? Speculate on the advantages of having G-proteins mediate the effects of a neurotransmitter.

Studies indicate that alcoholism may be associated with a particular allele

(form of a gene) for the D2 dopamine receptor. Suggest some scientific investigations that might further explore these possible genetic and physiological relationships.

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