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CHAPTER
14
The Autonomic Nervous System
Objectives
Overview
1. Define autonomic nervous system and explain its relationship to the peripheral nervous
system.
ANS Anatomy
4. For the parasympathetic and sympathetic divisions, describe the site of CNS origin,
locations of ganglia, and general fiber pathways.
ANS Physiology
5. Define cholinergic and adrenergic fibers, and list the different types of their receptors.
6. Describe the clinical importance of drugs that mimic or inhibit adrenergic or cholinergic
effects.
Homeostatic Imbalances of the ANS
9. Explain the relationship of some types of hypertension, Raynaud’s disease, and
autonomic dysreflexia to disorders of autonomic function.
Developmental Aspects of the ANS
10. Describe several effects of aging on the autonomic nervous system.
Suggested Lecture Outline
I. Overview (pp. 524–527, Figs. 14.1–14.2)
A. Comparison of the Somatic and Autonomic Nervous Systems (pp. 525–526; Figs.
14.1–14.2)
2. In the somatic nervous system, the cell bodies of the neurons are in the spinal cord and
their axons extend to the skeletal muscles they innervate.
5. There is overlap between the somatic and autonomic nervous systems, and most body
responses to changing internal and external stimuli involve both skeletal muscle
activity and visceral organ responses.
B. ANS Divisions (pp. 526–527; Fig. 14.3)
1. There are two ANS divisions, both usually serving the same visceral organs, but
having opposing effects.
II. ANS Anatomy (pp. 527–533; Figs. 14.3–14.7; Table 14.1)
A. Sympathetic and parasympathetic divisions differ in the site of origin, relative lengths of
fibers, and location of ganglia (p. 527, Fig. 14.3).
B. Parasympathetic (Craniosacral) Division (pp. 527–529; Figs. 14.3–14.4; Table 14.1)
1. The preganglionic axons extend from the CNS nearly all the way to the structures
to be innervated, where they synapse with postganglionic neurons in the terminal
ganglia.
C. Sympathetic (Thoracolumbar) Division (pp. 529–533; Figs. 14.3, 14.5–14.6; Table 14.1)
1. The sympathetic division supplies the visceral organs in the internal body cavities but
also all visceral structures in the somatic part of the body.
III. ANS Physiology (pp. 533–539; Fig. 14.8; Tables 14.2–14.4)
A. Neurotransmitters and Receptors (pp. 533–535; Table 14.2)
1. Cholinergic receptors, such as nicotinic and muscarinic receptors, bind acetylcholine.
2. Adrenergic receptors alpha and beta bind to epinephrine.
organs (p. 535; Table 14.3).
C. Interactions of the Autonomic Divisions (pp. 535–537; Table 14.4)
1. Most visceral organs receive dual innervation by both ANS divisions, allowing for a
dynamic antagonism to exist between the divisions and precise control of visceral
activity.
2. Sympathetic tone throughout the vascular system allows the firing rate of sympathetic
neurons to control the diameter of blood vessels, regulating systemic blood pressure.
3. Parasympathetic tone is usually dominant in the heart, digestive system, and urinary
tracts, maintaining normal homeostatic levels of function unless overridden by the
sympathetic system during stress.
D. Control of Autonomic Functioning (pp. 538–539, Fig. 14.8)
1. The brain stem appears to exert the most direct influence over autonomic functions.
IV. Homeostatic Imbalances of the ANS (p. 539)
A. Most autonomic disorders reflect exaggerated or deficient control of smooth muscle
(p. 539).
1. Hypertension, or high blood pressure, may result from an overactive sympathetic
vasoconstrictor response due to continuous high levels of stress.
V. Developmental Aspects of the ANS (p. 539)
A. Embryonic and fetal development of the autonomic nervous system (p. 539).
1. ANS preganglionic neurons and somatic motor neurons derive from the embryonic
neural tube.
B. In youth, ANS dysfunction is usually due to injury to the spinal cord or autonomic nerves
(p. 539).
C. In old age the efficiency of the ANS begins to decline, partly due to structural changes of
some preganglionic axon terminals (p. 539).
Cross References
Additional information on topics covered in Chapter 14 can be found in the chapters listed below.
1. Chapter 3: Membrane functions; membrane receptors
5. Chapter 18: The role of the sympathetic and parasympathetic pathways (as well as
epinephrine and norepinephrine) in medullary control of cardiac rate
Lecture Hints
1. Because the autonomic nervous system is more complex than the somatic nervous
system, it is worthwhile to spend some time comparing and contrasting the anatomy of
2. Emphasize that somatic efferent pathways consist of a motor neuron cell body in the
3. Point out that in many cases sympathetic and parasympathetic synapses use different
neurotransmitters—an essential characteristic in the dual nature of autonomic function.
This will be illustrated when discussing fight/flight and rest/digest responses.
Activities/Demonstrations
1. Audiovisual materials are listed in the Multimedia in the Classroom and Lab section of
this Instructor Guide (p. 387).
2. Without announcing what you will be doing, walk quietly into the lecture room, set your
Critical Thinking/Discussion Topics
1. Describe the role of beta-blockers in treating certain types of visceral disorders.
2. At certain times when people are very excited or are shocked suddenly, their bowels and/or
urinary sphincters lose control. In terms of the role of the ANS, why does this happen?
6. Why is sympathetic action diffuse and long lasting while parasympathetic is local and
short-lived? What would happen to body systems during a stressful situation if these
characteristics were reversed? How would anatomy have to be changed?
Library Research Topics
1. Do all animals have an autonomic nervous system? If so, how does it compare to ours?
2. The ANS regulates peristaltic waves of the GI tract. If the ganglia and/or fibers control-
ling this activity were damaged, what would happen? What bacterial agents or type of
trauma could cause this?
List of Figures and Tables
All of the figures in the main text are available in JPEG format, PPT, and labeled & unlabeled
format on the Instructor Resource DVD. All of the figures and tables will also be available in
Transparency Acetate format. For more information, go to www.pearsonhighered.com/educator.
Figure 14.1 Place of the ANS in the structural organization of the
nervous system.
Figure 14.2 Comparison of motor neurons in the somatic and autonomic
Parasympathetic and Sympathetic Divisions
Table 14.2 Cholinergic and Adrenergic Receptors
Table 14.3 Selected Drug Classes That Influence the Autonomic
Nervous System
Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
6. Involuntary nervous system is used to reflect the subconscious control of the ANS;
7. White rami communicantes contain myelinated preganglionic fibers that leave the spinal
nerve to enter the sympathetic trunk; gray rami communicantes represent postganglionic
fibers, are nonmyelinated, and enter the spinal nerve to travel to their ultimate destina-
tion. (p. 529)
8. Sympathetic activation of sweat glands—increase the production of sweat; eye pupils—
enlarge (dilate); adrenal medulla—releases norepinephrine and epinephrine; heart—
9. All effects listed above would be reversed by parasympathetic stimulation, except for
effects on the adrenal medulla, liver, and blood vessels. (p. 526)
10. All preganglionic fibers of the ANS and postganglionic fibers of the parasympathetic and
11. “Tone” in the divisions of the ANS refers to the firing rate of sympathetic and parasym-
pathetic neurons. Sympathetic tone determines the degree of constriction or dilation
12. Acetylcholine (cholinergic) receptor subtypes are nicotinic and muscarinic; norepineph-
rine (adrenergic) receptor subtypes are α1, α2, ß1, ß2, and ß3. See Table 14.3 for major
locations. (pp. 534–535)
13. The reticular formation nuclei in the brain stem are key to mediating ANS reflexes,
particularly those in the medulla. (p. 538)
15. The premise of biofeedback training is that we do not routinely exert voluntary controls
over our visceral activities because we have little conscious awareness of our internal
16. Elderly people often complain of constipation, dry eyes, and faintness when they change
position, such as standing up abruptly after sitting. (p. 539)
17. The autonomic motor pathway is a two-neuron pathway; the first neuron, the pregangli-
onic neuron, originates within the spinal cord, and synapses with the second neuron, the
postganglionic neuron. The synapse between these two neurons is located within an en-
largement along the nerve, the autonomic ganglion, located outside the CNS. Although
the axon extends away from the ganglion toward the effector cell, the cell body of the
postganglionic neuron originates within the ganglion itself. Because the cell body, the
metabolic center of the cell, is within the ganglion, “ganglionic neuron” is an appropriate
term. (p. 525)
Critical Thinking and Clinical Application Questions
1. Parasympathetic stimulation of the bladder via the release of acetylcholine increases
bladder tone and releases the urinary sphincters, a result that will be reproduced by
2. Nicotine may cause vascular spasms, causing skin temperature to drop, which may bring
on an attack. In addition, the drugs prescribed for Raynaud’s disease are vasodilators, and
nicotine would interfere with their action. (p. 539)
Suggested Readings
Ebadi, Manuchair. Pharmacodynamic Basis of Herbal Medicine. 2nd ed. Boca Raton: CRC
Press, 2007.
Kaufmann, H., et al. “Autonomic Failure as the Initial Presentation of Parkinson Disease and
Dementia with Lewy Bodies.” Neurology 63 (6) (May 2004): 1093–1095.
Ratcliffe, E., N. Farrar, and E. Fox. “Development of the Vagal Innervation of the Gut:
Steering the Wandering Nerve.” Neurogastroenterology and Motility 23 (10) (Oct. 2011):
898–911.
