Human Physiology, 14th edition (2016)

(Tina Sui) #1
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

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