AUTONOMIC NERVOUS SYSTEM

AUTONOMIC NERVOUS SYSTEM

I. Introduction: This is a Motor System: INVOLUNTARY Motor Neurons to SMOOTH MUSCLE (in the walls of hollow organs),

CARDIAC MUSCLE & GLANDS

II. Organization: Somatic (voluntary) versus Autonomic (involuntary)

- The Somatic (voluntary) Motor System

- The Autonomic Nervous System (ANS; involuntary, motor) uses 2 neurons to reach SMOOTH MUSCLE (in the walls of hollow organs), CARDIAC MUSCLE & GLANDS. (It does have ganglia)

A. 1st = preganglionic neuron:

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 of spinal cord (lateral horns are found from T1‑L2).

1. The first (preganglionic) neuron leaves the lateral horn, travels through the ventral root, enters the spinal nerve and leaves it via the white ramus communicans. It can then synapse with a second (postganglionic) neuron in either a paravertebral ganglion (23, aligned in what are referred to as the sympathetic trunk ganglia = sympathetic chain) or in a peripheral (= prevertebral = collateral) ganglion (4, anterior to the spinal cord).

B. PARASYMPATHETIC = Craniosacral

1. Cranial:

a. 1st neuron (preganglionic) cell bodies in brain stem (CNS). Their axons course through cranial nerves III, VII, IX & X.

IV. Functions

A. Most organs receive both sympathetic and parasympathetic innervation. The effects may be antagonistic (in opposition to each other) or cooperative (working together):

1. Antagonistic Effects:

		Parasympathetic	Sympathetic
1. Pupil		Circular M. (constricts)	Radial M. (dilates)
2. Glands
	a. Lacrimal	Stimulates
	b. Sweat		Stimulates
	c. Salivary		Inhibited
	d. Gastric	Stimulates
3. Heart Rate		Decreases	Increases
4. Digestive System		Increases Activity	Decreases Activity

2. Cooperative Effects:

	Parasympathetic	Sympathetic
1. Penis	Causes Erection	Causes Ejaculation

B. Some organs receive one or the other, either sym. or para. nerves:

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

4. Most blood vessels receive sym only. It causes constriction in visceral vessels and dilation in skeletal muscle vessels. A few vessels receive parasympathetic. It causes dilation (e.g., blood vessels in penis).