Autonomic Nervous System (ANS)
Visceral Efferent (VE) Pathway: nvolves 2 neurons
1. Preganglionic
neuron — cell body located in CNS; axon synapses in an autonomic ganglia
2. Postganglionic neuron — cell body in an autonomic
ganglion; axon innervates smooth muscle,
cardiac muscle or gland
dia......
.
ANS Divisions: basis for recognizing two divisions
Feature Sympathetic Parasympathetic
Distribution: ---------whole
body--------- viscera in body cavities; in head
Preganglionic origin: ---
thoracolumbar spinal cord --- sacral spinal cord &
brainstem
Postganglionic neuron: ------ usually adrenergic ------- always
cholinergic
Functional role: ------------fight
or flight------------ routine visceral operations
Functional Differences:
Structure ---------
Sympathetic-----------Parasympathetic
iris (pupil) ----------------------dilate ------------------------ constrict
heart----------increase rate
& force of contraction -----------
decrease rate
bronchi -------------------dilate ------------------------------ constrict
gut & bladder wall -----------inhibit motility ------------ excite
contraction
gut & bladder
sphincters --------------------contract -------------------
relax
cutaneous vessels -------------------constrict
------------------- doesn’t innervate
muscle vessels -----------dilate (cholinergic) -------------- doesn’t innervate
sweat glands
-----------------------secrete -------------------- doesn’t innervate
Autonomic
Pathways
Parasympathetic pathways:
dia..........
1.
Cranial nerves III, VII, and IX ....
later in the course.
2.
Cranial nerve X (vagus nerve)
innervates thoracic and abdominal viscera:
Preganglionic pathway: the vagus n.
branches travel to organs being innervated
Synapse: occurs within organs innervated, in
microscopic terminal ganglia
Postganglionic pathway: axons course
in submucosal or myenteric plexuses to reach innervation targets.
3. Sacral spinal cord innervates pelvic viscera:
Preganglionic pathway: from the sacral cord to pelvic plexus.
synapse: occurs in a pelvic ganglion within the pelvic
plexus.
Postganglionic pathway: branches from the pelvic plexus run
directly to pelvic viscera.
Sympathetic
Preganglionic Pathways
dia.......
Sympathetic Pathways to Six Regions
Head Region
Preganglionic path: ventral root; spinal n.; ramus communicans; sympathetic trunk; ansa
subclavia; and cervical sympathetic trunk.
Synapse: cranial cervical ganglion.
Postganglionic path: nerve plexuses run on external & internal carotid
arteries and their branches to reach target structures.
Neck Region
Preganglionic path: ventral root; spinal n.; ramus communicans; sympathetic trunk.
Synapse: cervicothoracic
ganglion.
Postganglionic path: vertebral nerve; rami communicantes; cervical spinal
nn.; dorsal or ventral branches to muscles & skin.
Body Wall and Limbs and Tail
Preganglionic path: ventral root; spinal n.; ramus communicans;
sympathetic trunk.
Synapse: sympathetic
trunk ganglia.
Postganglionic path: Rami communicantes;
spinal nn.; dorsal or ventral branches to muscles & skin
Thoracic Viscera
Preganglionic path: Ventral root; spinal n.; ramus communicans; sympathetic trunk.
Synapse: Cervicothoracic
& middle cervical ganglia
Postganglionic path: Cardiosympathetic nn. branch from ansa subclavia
Abdominal Viscera
Preganglionic path: Ventral root; spinal n.; ramus communicans; sympathetic trunk;
splanchnic nn
.
Synapse: Prevertebral
ganglia (left/right celiac, cranial mesenteric, caudal mesenteric, renal, and
gonadal ganglia) located in nerve plexuses along the aorta
Postganglionic path: nerve plexuses on abdominal
arteries supplying particular organs
Pelvic Viscera
Preganglionic path: ventral root; spinal n.; ramus communicans;
sympathetic trunk lumbar splanchnic nn.; caudal mesenteric
plexus
Synapse caudal mesenteric ganglion (also, synapses
in pelvic ganglia)
Postganglionic path: hypogastric n.; pelvic plexus; branches
directly to pelvic viscera (left/right)
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