Human Physiology, 14th edition (2016)

The Autonomic Nervous System 263

Sofia’s pupils were dilated for her eye exam by atropine,

a drug that specifically blocks muscarinic ACh receptors,

thus reducing the ability of postganglionic parasympa-

thetic axons to constrict her pupils. She attempted to

use biofeedback to quiet her anxiety, because the pulse

rate is determined by the heart rate, which is slowed

by increased parasympathetic (vagus) nerve activity.

The cold pill contained pseudoephedrine, which stimu-

lates vasoconstriction that dries the nasal mucosa but

can promote hypertension. She takes atenolol, how-

ever, which blocks the b 1 -adrenergic receptors in the

heart to slow the heart rate and lower the blood pres-

sure. The atenolol may also, less specifically, block the

b 2 - adrenergic receptors in the bronchioles to promote

asthma. To counteract this, Sofia used an asthma inhaler

that probably contained albuterol, a b 2 -agonist that pro-

motes relaxation of the bronchiolar smooth muscles to

help the bronchioles dilate.

See the additional chapter 9 Clinical Investigation on

Autoimmune Autonomic Neuropathy in the Connect site for

this text.

Clinical Investigation SUMMARY

Summary

norepinephrine) into the blood in response to

stimulation.

B. Preganglionic parasympathetic fibers originate in the brain

and in the sacral levels of the spinal cord.

1. Preganglionic parasympathetic fibers contribute to

cranial nerves III, VII, IX, and X.

2. The long preganglionic fibers of the vagus (X) nerve

synapse in terminal ganglia located next to or within

the innervated organ. Short postganglionic fibers then

innervate the effector cells.

3. The vagus provides parasympathetic innervation to the

heart, lungs, esophagus, stomach, liver, small intestine,

and upper half of the large intestine.

4. Parasympathetic outflow from the sacral levels of the

spinal cord innervates terminal ganglia in the lower half

of the large intestine, in the rectum, and in the urinary

and reproductive systems.

9.3 Functions of the Autonomic Nervous

System 251

A. The sympathetic division of the autonomic system activates

the body to “fight or flight” through adrenergic effects. The

parasympathetic division often exerts antagonistic actions

through cholinergic effects.

9.1 Neural Control of Involuntary Effectors 244

A. Preganglionic autonomic neurons originate in the brain or
spinal cord; postganglionic neurons originate in ganglia
located outside the CNS.
B. Smooth muscle, cardiac muscle, and glands receive auto-
nomic innervation.

1. The involuntary effectors are somewhat independent of
   their innervation and become hypersensitive when their
   innervation is removed.


2. Autonomic nerves can have either excitatory or
   inhibitory effects on their target organs.

9.2 Divisions of the Autonomic Nervous
System 246

A. Preganglionic neurons of the sympathetic division originate
in the spinal cord, between the thoracic and lumbar levels.

1. Many of these fibers synapse with postganglionic neurons
   whose cell bodies are located in a double chain of
   sympathetic (paravertebral) ganglia outside the spinal cord.


2. Some preganglionic fibers synapse in collateral
   (prevertebral) ganglia. These are the celiac, superior
   mesenteric, and inferior mesenteric ganglia.


3. Some preganglionic fibers innervate the adrenal
   medulla, which secretes epinephrine (and some