Chapter 14
Autonomic Nervous System
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System of motor neurons innervating
smooth and cardiac muscle and glands
Autonomic nerves make adjustments to
many changes identified by the sensory
division of the PNS
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ANS differs from the SNS in:
Their effectors
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SNS innervates skeletal muscle and ANS
innervates smooth and cardiac muscle and
glands
Efferent pathways
SNS - cell bodies of the motor neuron are
in the CNS, and their axons extend in
spinal nerves all the way to skeletal
muscles
ANS - two neuron chain
 The cell body of the first neuron
(preganglionic neuron) resides in the brain or
spinal cord
 Its axon (preganglionic axon) synapses with
the second motor neuron (ganglionic neuron)
in an autonomic ganglion outside the CNS
 The axon of the ganglionic neuron
(postganglionic axon) extends to the effector
organ.
Synapse in a ganglia
Parasympathetic: intramural ganglia: close to the
effector organ
Sympathetic: chain (paraverterbral) ganglia
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Target organ responses - neurotransmitter
effects
SNS - acetylcholine released at their
synapse
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ANS - norepinephrine, epinephrine
(adrenergic)
and acetylcholine (cholinergic)
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Divisions of the ANS
Parasympathetic and sympathetic
Action via ANS is by dual innervation
(divisions counterbalance each other's
activities)
Parasympathetic division in general is
most active in nonstressful situations
- rest and digest
Sympathetic (stress) division in general is
most active in emergency or threatening
situations - "fight-or-flight"
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Parasympathetic:
- pupils constrict
- stimulates salivary, lacrimal and
pancreas glands
- decrease heart rate
- causes contraction and emptying of
hollow organs: bladder, gallbladder,
stomach, intestines (peristalsis)
- vasodilation of penis (erection) and
clitoris
- no effect on blood vessels
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Sympathetic:
- dilates pupils
- inhibits secretion of glands
- stimulates sweating
- stimulates arrector pili
- stimulates medulla of adrenal gland to secrete
epi/norepinephrine
- increases heart rate
- decreases digestive processes
- decreases urine output
- causes ejaculation
- stimulates glycogenolysis in liver (glucose
release)
- blood vessel constriction/dilation and blood
coagulation
- bronchiole dilation
Parasympathetic
Craniosacral division
Cranial:
CN nerves III, VII, IX and X
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CN III (Oculomotor):
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Preganglionic fibers: from oculomotor nuclei in
the midbrain synapses in the ciliary ganglion
(in eye)
Postganglionic fiber: innervates smooth
muscle of eye
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Pupil constriction and lens movement to cause
focusing
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Facial nerve (VII)
Preganglionic fibers: from lacrimal nuclei in the
pons synapses in the pterygopalatine ganglia
Postganglionic fiber: innervates lacrimal glands
of eye
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Lubrication of eye and tear formation
Preganglionic fibers: from superior salivatory
nuclei in the pons synapses in the
submandibular ganglia
Postganglionic fibers: innervate submandibular
and sublingual salivary glands
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Production of saliva and secretion of salivary enzymes
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Glossopharyngeal nerve (IX)
Preganglionic fibers: from the inferior salivary
nuclei in the medulla synapses in the otic
ganglia
Postganglionic fibers: innervate the parotid
salivary gland
Vagus nerve (X) “wanderer”
Preganglionic fibers from the dorsal motor
nuclei (nucleus ambiguus) of the medulla
synapses in terminal ganglia located within the
walls of the target organ (intramural)
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Intramural ganglia ....effects:
Heart -decreases/steadies heart rate and
constricts coronary veins
Lung - constricts bronchioles
Gall bladder - expel bile
Stomach - stimulates secretion of enzymes
Intestines - increase motility (peristalsis)
and relaxes sphincters
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Sacral Outflow
Preganglionic fibers from lateral gray
matter of spinal cord in segments S2-S4
synapse in terminal ganglia within walls of
the target organ
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Intramural ganglia....effects:
 Distal large intestines - relaxes sphincters
 Bladder - contraction of smooth muscle of
bladder wall; relaxes urethral sphincter promotes voiding
 Genitalia - causes penile and clitoral
erection
Sympathetic Nervous System
Thoracolumbar division
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All preganglionic fibers of sympathetic division
arise from cell bodies of preganglionic neurons
located in lateral horn of the spinal cord
segments T1-L2
These fibers exit the ventral roots of spinal
nerves and continue through branches called
white rami communicantes before entering the
paravertebral sympathetic ganglia located in
chains along side the spine. These ganglia make
up the sympathetic trunk
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Once in the paravertebral ganglia the
preganglionic fiber can:
1- Synapse with a postganglionic neuron
within the same ganglion .
2- Ascend/descend within sympathetic
trunk to synapse with another
paravertebral ganglion.
3- Pass through the ganglion (splanchnic
nerve) and emerge from the sympathetic
chain without synapsing until they reach a
collateral ganglia (prevertebral)
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Preganglionic fibers innervating the head and
neck arise from spinal cord levels T1-T6. These
fibers ascend through the sympathetic trunk
and synpase with postganglionic fibers in the
cervical ganglia
- superior
- middle
- inferior
Superior cervical ganglion:
- Stimulates dilator muscles of irises
- Inhibits nasal and salivary glands
- Stimulates copious sweating
- Stimulates arrector pili muscle to contract
- Causes blood vessel vasodilation
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Middle cervical ganglia - innervates heart
and skin
Inferior cervical ganglia (stellate ganglion)
innervates heart, aorta, dilates
bronchioles, constrict esophageal
sphincter.
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Synapses in Collateral Sympathetic
Ganglion:
Preganglionic fibers of T5-L2 synapse in
prevertebral ganglia. Fibers enter and
leave without synapsing and form several
nerves collectively called splanchnic
nerves (greater, lesser, and lumbar)
Splanchnic nerves synapse at abdominal
aortic plexus that clings to surface of
abdominal aorta
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Synapses occur at ganglia of plexus:
Greater splanchnic nerve
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Celiac ganglion - innervates stomach
(decrease muscle activity/constricts pyloric
sphincter), adrenal medulla (secretes
epinephrine/norepinephrine), liver
(epinephrine stimulates liver to release
glucose), kidney (vasoconstriction, decrease
urine output), intestine (decrease smooth
muscle activity)
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Lesser splanchnic nerve
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Lumbar splanchnic nerve
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Superior mesenteric (via celiac) ganglion innervates small intestine
Inferior mesenteric ganglion - innervates large
intestine
Lumbar splanchnic nerve
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Hypogastric ganglion - innervates bladder and
urethra (causes relaxation of smooth muscle
of bladder wall and constricts urethral
sphincter/inhibits voiding), genitalia (causes
ejaculation in males and vaginal contractions
in females)