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
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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:
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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
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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
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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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