Ganong's Review of Medical Physiology, 23rd Edition

268
SECTION III
Central & Peripheral Neurophysiology

is the innervation of salivary glands. Parasympathetic activa-
tion causes release of watery saliva, while sympathetic activa-
tion causes the production of thick, viscous saliva.
The two divisions of the ANS can also act in a synergistic or
cooperative manner in the control of some functions. One
example is the control of pupil diameter in the eye. Both sym-
pathetic and parasympathetic innervations are excitatory, but
the former contracts the radial muscle to cause mydriasis and
the latter contracts the sphincter (or constrictor) muscle to
cause meiosis. Another example is the synergistic actions of
these nerves on sexual function. Activation of parasympa-
thetic nerves to the penis increases blood flow and leads to
erection while activation of sympathetic nerves to the penis
causes ejaculation.
There are also several organs that are innervated by only one
division of the ANS. In addition to the adrenal gland, most
blood vessels, the pilomotor muscles in the skin (hair follicles),
and sweat glands are innervated exclusively by sympathetic
nerves. The lacrimal muscle (tear gland), ciliary muscle (for
accommodation for near vision), and the sublingual salivary
gland are innervated exclusively by parasympathetic nerves.

PARASYMPATHETIC CHOLINERGIC

& SYMPATHETIC

NORADRENERGIC DISCHARGE

In a general way, the functions promoted by activity in the

cholinergic division of the autonomic nervous system are

those concerned with the vegetative aspects of day-to-day liv-

ing. For example, parasympathetic action favors digestion and

absorption of food by increasing the activity of the intestinal

musculature, increasing gastric secretion, and relaxing the py-

loric sphincter. For this reason, the cholinergic division is

sometimes called the anabolic nervous system

.

The sympathetic (noradrenergic) division discharges as a

unit in emergency situations and can be called the catabolic

nervous system. The effects of this discharge prepares the indi-

vidual to cope with an emergency. Sympathetic activity dilates

the pupils (letting more light into the eyes), accelerates the

heartbeat and raises the blood pressure (providing better per-

fusion of the vital organs and muscles), and constricts the

blood vessels of the skin (which limits bleeding from wounds).

Uterus

Variable

α

1

Contraction (pregnant)

β

2

Relaxation

Male sex organs

Erection

α

1

Ejaculation

Skin

Pilomotor muscles —

α

1

Contraction

Sweat glands —

α

1

Slight, localized secretion

b

M Generalized abundant, dilute
secretion
Liver
—
α
1
,
β
2
Glycogenolysis
Pancreas
Exocrine glands Increases secretion
α
Decreases secretion
Endocrine glands —
α
2
Inhibits secretion
Salivary glands
Profuse, watery secretion
α
1
Thick, viscous secretion
β
Amylase secretion
Lacrimal glands
Secretion —
Adipose tissue
—
α
2
,
β
3 Lipolysis
aA dash means these cells are not innervated by this division of the autonomic nervous system.
bOn palms of hands and in some other locations (“adrenergic sweating”).

Modified from Hardman JG, Limbird LE, Gilman AG (editors): Goodman and Gilman’s The Pharmacological Basis of Therapeutics, 10th ed. McGraw-Hill, 2001.

TABLE 17–1 Responses of some effector organs to autonomic nerve activity. (Continued)

Sympathetic Nervous System

Effector Organs Parasympathetic Nervous System Receptor Type Response