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Autonomic Nervous System (Ch. 16)
Human Anatomy lecture
 Ignore excess physiology in text
I. Comparison of Somatic and Autonomic Nervous System
 KNOW Fig. 16.2 & Table 16.1 (mostly)
A. Somatic N.S. - voluntary
- Effector - skeletal muscle
- Efferent Path - single motor neuron
- Response - always excitatory
- Neurotransmitter - acetylcholine (Ach)
B. Autonomic N.S. (ANS) - involuntary
- Effector - smooth, cardiac muscle, and glands (= visceral motor system)
- Efferent Path - 2 motor neurons with synapse in ganglion
 1st neuron = preganglionic
 2nd neuron = postganglionic (ganglionic)
- Response - excitatory or inhibitory
- Neurotransmitter - acetylcholine or norepinephrine (NE)
C. ANS has 2 divisions - Parasympathetic and Sympathetic
-- most organs receive dual innervation (cf Fig. 16.4 & 16.7)
-- usually have opposite actions (Ex: Fig. 16.9)
II. Anatomy of autonomic pathways
A. Overview (reexamine Fig. 16.2b) -- not purely PNS as commonly implied
preganglionic neuron  cell body in CNS
 axon  myelinated; in spinal or cranial nerve

ganglion  pre- & post- synapse here
contains
postganglionic (ganglionic) neuron  entirely in the PNS
cell body
 axon  unmyelinated

effector
B. Parasympathetic N.S. – Fig 16.7
1. preganglionic neurons
- cell bodies in the brain and lateral horns S2 - S4 = craniosacral outflow
- axons emerge from CNS via
 cranial nerves III, VII, IX, and X (80%)
“viscera”
 anterior roots & spinal nerves S2 - S4  give rise to pelvic splanchnic
nerves
ANS -- Page 1 of 3
2. Parasympathetic ganglia
- contain cell body of postganglionic neuron
- called terminal ganglia - near or in wall of effector organ
So: parasymp. preganglionic fibers are long
3. Postganglionic axons
- short
C. Sympathetic N.S. – Fig. 16.4
1. Preganglionic neurons
- cell bodies in lateral horns T1 - L2 = thoracolumbar outflow
- axons emerge via anterior roots
2. Sympathetic ganglia
a. sympathetic chain (paravertebral) ganglia (22 - 25) - vertical row on
either side of vertebral column
b. collateral (prevertebral) ganglia (3) - anterior to vertebral column, near
large arteries
c. adrenal medulla
- both types are close to spinal cord, so sympathetic preganglionic fibers are short
- sympathetic preganglionic fibers branch and may contact 10-20 postganglionic
neurons = divergence
- sympathetic preganglionic axons have 4 potential destinations:
 KNOW FIG. 16.5
 reach sympathetic chain ganglion via white communicating ramus
or
 many do not stop at the ganglion: branch and go up or down in the
sympathetic trunk
or
 may exit in splanchnic nerve which carries preganglionic fibers to a
collateral ganglion
or
 may continue to the adrenal medulla, which is also a collection of
postganglionic neurons (anaxonic)
3. postganglionic axons
- long, to reach effector
- travel from sympathetic chain ganglion via
 gray communicating ramus into spinal nerve
or
 other sympathetic nerves to viscera
- may contact several effectors (more divergence)
ANS -- Page 2 of 3
D. Autonomic plexuses – Fig. 16.6 & 16.4
- near the heart, lung and gut
- fibers from both divisions mingle to form nerve networks
Ex.: “solar plexus” = knock-out punch
 KNOW Table 16.3, p. 452
III. Functions
A. both systems constantly active at low levels = autonomic tone (Fig. 16.10)
- balance of activity shifted to meet body’s needs
B. Sympathetic
- “Fight-or-Flight” response
- “E-situations”
Emergency
Exercise
Embarrassment
- typically widespread, more commonly mass discharged (Rule #1?)
-“sympatho-adrenal” system contributes to widespread effect
C. Parasympathetic
- “Feed and Breed” response
- energy conservation - restorative system
- “SLUDD” = Salivation
Lacrimation
Urination
Defecation
Digestion
ANS -- Page 3 of 3