Control of Involuntary Effectors (smooth muscle of gut, blood vessels, lungs, reproductive tract, and pupils; cardiac muscle; glands)

Maintains homeostasis.

ANS is the visceral motor division of the nervous system. Two neurons involved: one neuron has cell body in CNS and terminates at a paravertebral ganglion or autonomic ganglion near visceral organ. Second neuron has cell body in ganglion and its axon innervates a visceral effector.

CNS --> Pre-ganglionic fiber---> Ganglion ----> Post-ganglionic fiber---> Visceral Effector

Visceral Effectors: smooth muscle, cardiac muscle, glands (salivary, lacrimal)

ANS has 2 divisions:

1) Sympathetic (thoracolumbar in origin). Autonomic ganglia are paravertebral ganglia. Short preganglionic fiber, long postganglionic fiber.

2) Parasympathetic (craniosacral in origin). Autonomic ganglia are near effector organs. Long preganglionic, short postganglionic fibers

Autonomic Connections of Spinal Cord

Overview Site

Sympathetic -- "fight or flight". Stimulates heart, blood glucose rises, blood diverted away from viscera to skeletal muscles. Can be activated as a whole.

Neurotransmitters used: ACh, preganglionic; epinephrine (adrenalin) or norepinephrine, postganglionic.

Parasympathetic--related to relaxation, vegetative functions. Blood goes to viscera, heart beat slows. Not activated as a whole normally.

Neurotransmitters used: ACh at both preganglionic and postganglionic synapses.

Sympathetic and Parasympathetic systems are usually antagonistic:

Examples heart rate (sym. increases, parasym. decreases) and control or iris of eye (sym. dilates, parasym constricts).

There are some cooperative effects; for example, urination and sexual response.

Erection involves vasodilation induced by parasympathetic NS while ejaculation and orgasm involves vasoconstriction induced by sympathetic nervous system.

Some effectors are only innervated by one system--adrenal medulla, arrector pili and sweat glands are only innervated by sympathetic.

Adrenal medulla is actually a sympathetic ganglia that lacks postganglionic fibers. It dumps epinephrine and norepinephrine directly into blood. Acts to generate a wide-spread sympathetic response -- increases heart rate, blood pressure, increases rate and depth of breathing, blood flow to muscles and away from viscera.

Even though 3 transmitters are involved in ANS, they can have a variety of effects because of different receptors on effectors.

Cholinergic Receptors: Respond to Acetylcholine (ACh). Two types of receptors found:

Atropine (belladonna) is an anticholinergic drug (an muscarinic receptor antagonist). It binds to muscarinic receptors and prevents ACh from exerting its normal effect. When used on eye, pupil dilates -- mimics sympathetic NS by blocking parasympathetic NS ability to constrict pupil. Also used in diarrhea medications and as an antidote for muscarine and pesticide poisoning.

Note: Belladonna means 'pretty woman': It was used as a cosmetic -- dilated pupils do make people more appealing (that "come hither" look?)

Trivia Quiz: Who was famous for singing "Oh, Pretty Woman?" Who starred in the movie "Pretty Woman"?
I'll use a lifeline, Regis. Phone a friend?
(Don't confuse "Oh, Pretty Woman" with "Pretty Woman" of 2 Live Crew).

Curare (poison darts of Amazonian Indians) binds to nicotinic receptors and causes paralysis. Used in surgery.

Alpha-bungarotoxin (cobra venom) binds to nicotinic receptors and causes paralysis. Used experimentally.

Adrenergic Receptors: receptors for epinephrine and norepinephrine

Five major types: alpha 1 & 2, beta 1 & 2 & 3

Variations in gene are associated with ability to gain weight.

Distinguishing receptors is important pharmacologically. For example, asthma treatment. Asthma attack: bronchioles constrict. If treated with epinephrine heart rate and blood pressure would be affected. Modern asthma medications activate b2 receptors only.

"Beta-blockers" used for coronary patients or for high blood pressure block primarily b1 receptors.

The Autonomic Nervous System: from Neuroscience for Kids. Good, basic overview, even for older kids!
Problems associated with the ANS Horners, Sympathectomy, Shock(nursing source)

More Problems associated with the ANS


Hyperhidrosis: excessive sweating, typically palms. May be treated via surgery (cut sympathetic trunk serving hands)