Chapter 7

Automatic Nervous System


I. Introduction:

This is a Motor System: Involuntary Motor Neurons to SMOOTH MUSCLE, CARDIAC MUSCLE, & GLANDS

II. Organization:

The Somatic (voluntary) Motor System uses a single neuron to reach SKELETAL MUSCLES. The Autonomic Nervous System (ANS; involuntary, motor) uses 2 neurons to reach SMOOTH MUSCLE, CARDIAC MUSCLE, & GLANDS.

A. 1st = preganglionic neuron: cell body in CNS

B. 2nd = postganglionic neuron: cell body in a ganglion (an aggregation of cell bodies) in the PNS

III. Structure

A. SYMPATHETIC = Thoracolumbar: 1st neuron cell body in lateral horn (lateral horns are found from T1-L2)

1. The first (preganglionic) neuron leaves the lateral horn and will synapse with the second (postganglionic) neuron in either a paravertebral ganglion (in the sympathetic chain) or in a prevertebral (collateral) ganglion.


1. Cranial:

a. 1st neuron (preganglionic) cell bodies in brain stem (CNS). Their axons course through cranial nerves III, VII, IX, & X (Refer to lecture on Cranial Nerves; note involuntary motor activities = parasympathetic).

b. 1st axons synapse with 2nd neurons in Terminal Ganglia located next to or within the organs they innervate

2. Sacral:

a. 1st neuron (preganglionic) cell bodies in Lateral Gray Matter. Their axons go to Terminal Ganglia in or near lower 1/2 of large intestine, urinary bladder, and reproductive organs

IV. Functions

A. Organs with Dual Innervation: Most organs receive both sym. and para. innervation. In this situation the effects may be antagonistic, complementary, or cooperative.

1. Antagonistic Effects:

Sym Para

a. Heart Rate increase decrease

b. Dig. Tract

i. Sm mus. relax contract

ii. Pancreas inhib. stim.

iii. Gastric glnds inhib. stim.

c. Urinary System

i. Sphincter con. rel.

d. Resp. system

i. Sm. M. of tubes rel. con.

e. Eye

i. Pupil Radial M. Circular M.

(dilate) (constrict)

ii. Lacrimal glnd. inhib. stim.

f. Reprod. System dec. inc.

g. Blood vessels con.(most) rel.(few)

2. Complementary Effects:Sym Para

a. Salivary gland thick thin

3. Cooperative Effects:

Sym Para

a. Urinary Sys.

i. Bladder aids tone con.

b. Reprod. Sys.

i. Penis ejacul. erect.

B. Organs without Dual Innervation:

1. Adrenal Gland: the sym. stimulates the release of epinephrine and norepinephrine (enhances sym. effects).

2. Arrector pili muscles: receives sym. only; causes hairs to stand up.

3. Sweat glands: receives sym only; increases output

4. Most blood vessels: receive sym only; causes constriction. A few receive para. It causes dilation (e.g., blood vessels in penis)


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