Nerves, Nerve Fibers, and Ganglia

Objectives

When you have completed this section, you should be able to

• describe the structure of a nerve;
• explain how nerves and nerve fibers are classified; and
• describe the structure of a ganglion and the relationship of ganglia to peripheral nerves.

Think About It

How does the structure of a nerve compare to that of a skeletal muscle (see chapter 11)? Which of the descriptive terms for nerves have similar counterparts in muscle histology?

Key Point Review

1. Distinguish between a nerve and a nerve fiber.

2. Describe the relationship of the endoneurium, perineurium, and epineurium to the nerve fibers of the PNS.

3. Distinguish between somatic and visceral nerve fibers and between general and special nerve fibers.

4. Describe the structure of a ganglion.

The Cranial Nerves

Objectives

When you have completed this section, you should be able to

• list the cranial nerves by name and number;
• identify where each cranial nerve originates and terminates; and
• state the functions of each cranial nerve.

Key Point Review

5. List the purely sensory cranial nerves and state the function of each.

6. What is the only cranial nerve to extend beyond the head-neck region?

7. If the oculomotor, trochlear, or abducens nerve were damaged, the effect would be similar in all three cases. What would that effect be?

8. Which cranial nerve supplies more of the head than any other?

9. Name two cranial nerves involved in the sense of taste.

The Spinal Nerves

Objectives

When you have completed this section, you should be able to

• describe the attachment of a spinal nerve to the spinal cord;
• trace the branches of a spinal nerve distal to its attachment;
• name the five plexuses of spinal nerves and describe their general anatomy;
• name some major nerves that arise from each plexus;
• explain the relationship of dermatomes to the spinal nerves.

Think About It

Do you think the meningeal branch is composed of afferent fibers, efferent fibers, or both? Explain your reasoning.

Key Point Review

10. What is meant by the dorsal and ventral roots of a spinal nerve? Which of these is sensory and which is motor?

11. Where are the somas of the dorsal root located? Where are the somas that supply the ventral root?

12. List the five plexuses of spinal nerves and state where each one is located.

13. State which plexus gives rise to each of the following nerves: axillary, ilioinguinal, obturator, phrenic, pudendal, radial, and sciatic.

Somatic Reflexes

Objectives

When you have completed this section, you should be able to

• define reflex and explain how reflexes differ from other motor actions;
• describe the general components of a typical reflex arc; and
• explain how the basic types of spinal reflexes function.

Key Point Review

14. Name five structural components of a typical spinal reflex arc. Which one of these is absent from a monosynaptic reflex arc?

15. State the function of each of the following in a muscle spindle: intrafusal fiber, annulospiral ending, and motor neuron.

16. Explain how nerve fibers in a tendon sense the degree of tension in a muscle.

17. Why must the withdrawal reflex, but not the stretch reflex, involve a polysynaptic reflex arc?

18. Explain why the crossed extensor reflex must accompany a withdrawal reflex of the leg.

The Autonomic Nervous System: Introduction and Anatomy

Objectives

When you have completed this section, you should be able to

• explain how the autonomic nervous system and the somatic nervous system differ in form and function;
• explain how the two divisions of the autonomic nervous system differ in general function;
• identify the anatomical components of the sympathetic and parasympathetic divisions; and
• discuss the relationship of the adrenal glands to the sympathetic nervous system.

Think About It

Draw a negative feedback loop to show how autonomic effects on the heart contribute to homeostasis.

Key Point Review

19. In what ways is an autonomic reflex arc like a somatic motor reflex arc? In what ways does it differ?

20. Explain why the sympathetic division is also called the thoracolumbar division in spite of the fact that its chain of paravertebral ganglia extends all the way from the cervical to the sacral region.

21. Describe or diagram the structural relationships among the following: preganglionic fiber, postganglionic fiber, ventral ramus, gray ramus, white ramus, and paravertebral ganglion.

22. Explain in anatomical terms why the parasympathetic division affects target organs more selectively than the sympathetic division does.

23. Trace the pathway of a parasympathetic fiber of the vagus nerve from the medulla oblongata to the small intestine.

The Autonomic Nervous System: Physiology

Objectives

When you have completed this section, you should be able to

• name the neurotransmitters that are employed at different synapses of the ANS;
• name the kinds of receptors that exist for these neurotransmitters and explain how these receptor types relate to autonomic effects on target organs;
• explain how the ANS controls many target organs through dual innervation;
• explain how control is exerted in the absence of dual innervation; and
• discuss the ways in which the ANS is governed by various levels of the CNS.

Think About It

It is noted in table 15.11 that the sympathetic nervous system has an a-adrenergic effect on blood platelets and promotes clotting. How can this be, considering that the platelets are drifting cell fragments in the bloodstream and have no nerve fibers leading to them?

Key Point Review

24. Summarize the locations of nicotinic and muscarinic receptors in the ANS.

25. What second messenger is involved in the action of a2, ß1, and ß2 adrenergic receptors but not a1 receptors? What second messenger is involved in a1 receptors?

26. Explain what is meant by dual innervation and give some examples.

27. Describe how the sympathetic division can control blood flow in the absence of dual innervation.

28. Cite evidence indicating that the ANS is subject to cerebral influence.

Copyright ©1998 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use and Privacy Policy.
McGraw-Hill Higher Education is one of the many fine businesses of The McGraw-Hill Companies.
For further information about this site contact mhhe_webmaster@mcgraw-hill.com.