Ganong's Review of Medical Physiology, 23rd Edition

CHAPTER 17The Autonomic Nervous System 271

CHAPTER SUMMARY

■ Preganglionic sympathetic neurons are located in the IML of the

thoracolumbar spinal cord and project to postganglionic neurons

in the paravertebral or prevertebral ganglia or the adrenal medul-

la. Preganglionic parasympathetic neurons are located in motor

nuclei of cranial nerves III, VII, IX, and X and the sacral IML.

■ Nerve terminals of postganglionic neurons are located in

smooth muscle (eg, blood vessels, gut wall, urinary bladder),

cardiac muscle, and glands (eg, sweat gland, salivary glands).

■ Acetylcholine is released at nerve terminals of all preganglionic

neurons, postganglionic parasympathetic neurons, and a few

postganglionic sympathetic neurons (sweat glands, sympathetic

vasodilator fibers). The remaining sympathetic postganglionic

neurons release norepinephrine.

■ Sympathetic activity prepares the individual to cope with an

emergency by accelerating the heartbeat, raising blood pressure

(perfusion of the vital organs), and constricting the blood ves-

sels of the skin (limits bleeding from wounds). Parasympathetic

activity is concerned with the vegetative aspects of day-to-day

living and favors digestion and absorption of food by increasing

the activity of the intestinal musculature, increasing gastric se-

cretion, and relaxing the pyloric sphincter.

■ Ganglionic transmission is blocked by N2 nicotinic antagonists.

Postganglionic cholinergic transmission is blocked by musca-

rinic antagonists. Postganglionic adrenergic transmission is

blocked by antagonists of α 1 , β 1 , or β 2 adrenoreceptors, depend-

ing on the target organ.

■ The enteric nervous system is located within the wall of the di-

gestive tract and is composed of the myenteric plexus (control of

digestive tract motility) and the submucosal plexus (regulates

gastrointestinal blood flow and epithelial cell function).

MULTIPLE-CHOICE QUESTIONS

For all questions, select the single best answer unless otherwise directed.

1. Which of the following drugs would not be expected to increase
   sympathetic discharge or mimic the effects of increased sympa-
   thetic discharge?
   A) Prazosin
   B) Neostigmine
   C) Amphetamine
   D) Isoproterenol
   E) Methoxamine

FIGURE 17–6 Pathways that control autonomic responses. Direct projections (solid lines) to autonomic preganglionic neurons include
the hypothalamic paraventricular nucleus, parabrachial nucleus, nucleus of the solitary tract, ventrolateral medulla, and medullary raphé (not
shown). Indirect projections (dashed lines) include the cerebral cortex, amygdala, and periaqueductal grey matter. (From Kandel ER, Schwartz JH,
Jessell TM [editors]: Principles of Neural Science, 4th ed. McGraw-Hill, 2000.)

Periaqueductal

gray matter

Parabrachial

nucleus

Dorsal motor

vagal nucleus

Nucleus of the

solitary tract

Cortex

Parasympathetic

input

Sympathetic

input

Amygdala

Hypothalamus

Nucleus ambiguus

Ventrolateral

medulla

Intermediolateral

cell column

Heart