Introduction to Autonomics

Gross Anatomy


Autonomic Nervous System


Anatomy Tables for Today's Topic

Comparison of the Sympathetic and Parasympathetic Divisions of the Autonomic Nervous System
Definitions - Parts of the Sympathetic Nervous System

Comparison of the Sympathetic and Parasympathetic Divisions
of the Autonomic Nervous System

Feature Sympathetic Division Sacral Part of Parasympathetic Division Cranial Part of Parasympathetic Division
location of presynaptic nerve cell bodies intermediolateral cell column in the gray matter of spinal cord levels T1-L2 intermediate gray matter in spinal cord levels S2-S4 cranial nn. nuclei
axons exit the spinal cord through ventral roots ventral roots na
axons leave the spinal nerve through white rami communicans (spinal nerves T1-L2) pelvic splanchnic nerves (spinal nerves S2-S4) na
axons return to the spinal nerve for peripheral distribution through gray rami communicans (all vertebral levels) na na
postsynaptic nerve cell bodies are located in the paravertebral ganglia (sympathetic trunk) or prevertebral ganglia; medulla of suprarenal is considered a special postganglionic cell type terminal ganglia terminal ganglia
presynaptic axon length long long long; vagus n. has the longest presynaptic parasympathetic axons
postsynaptic axon length long (because they often travel on the surfaces of blood vessels to the organ to be innervated) short (because terminal ganglia are in or on the organ to be innervated) short (because terminal ganglia are in or on the organ to be innervated)
named nerves that carry postsynaptic axons branches of spinal nerves, perivascular plexuses which are named for the vessel (celiac, superior mesenteric, etc.) none (synapse occurs in or on the organ innervated) none (synapse occurs in or on the organ innervated)

Definitions - Parts of the Sympathetic Nervous System

Nerve Source Branches Motor Sensory Notes
spinal n. formed at the point where the dorsal and ventral rootlets meet; it ends where the dorsal and ventral primary rami diverge dorsal primary ramus; ventral primary ramus to skeletal mm.; some levels carry preganglionic sympathetic axons (T1-L2) general sense (touch, pressure, pain, heat, cold, etc.) from the entire surface of the neck, trunk and extremities; visceral pain (via the white ramus communicans and the sympathetic nervous system) located at the intervertebral foramen; there are 31 pairs of spinal nerves - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
ventral primary ramus first branch off of the ventral side of the spinal nerve numerous to skeletal mm. of the neck, trunk and extremities; sympathetic innervation to the skin general sense (touch, pressure, pain, heat, cold, etc.) to the skin of the trunk (except the back) and extremities; visceral pain via the white rami of the sympathetic nervous system (T1-L2) a mixed nerve containing both motor and sensory fibers
sympathetic chain ganglia preganglionic sympathetic fibers arrive via white rami communicantes of ventral primary rami of spinal nerves T1-L2 postganglionic sympathetic fibers depart via gray rami communicantes to all spinal nn.; internal & external carotid nn.; cervical cardiac brs.; thoracic direct visceral brs.; greater, lesser & least thoracic splanchnic nn.; lumbar splanchnic nn.; sacral splanchnic nn. dilator pupillae, vascular smooth muscle, arrector pili muscles, sweat glands, suprarenal medulla, heart, lungs and gut pain from viscera located lateral to the vertebral bodies in the neck, thorax & abdominopelvic cavity; the ganglia plus their interconnecting fibers are also known as the sympathetic trunk; preganglionic cell bodies are located in the intermediolateral gray matter of spinal cord levels T1-L2
paravertebral ganglia preganglionic sympathetic fibers arrive via white rami communicantes of ventral primary rami of spinal nerves T1-L2 postganglionic sympathetic fibers depart via gray rami communicantes to all spinal nn.; internal & external carotid nn.; cervical cardiac brs.; thoracic direct visceral brs.; greater, lesser & least thoracic splanchnic nn.; lumbar splanchnic nn.; sacral splanchnic nn. dilator pupillae, vascular smooth muscle, arrector pili muscles, sweat glands, suprarenal medulla, heart, lungs and gut pain from viscera located lateral to the vertebral bodies in the neck, thorax & abdominopelvic cavity; the ganglia plus their interconnecting fibers are also known as the sympathetic trunk; preganglionic cell bodies are located in the intermediolateral gray matter of spinal cord levels T1-L2
prevertebral ganglia splanchnic nn. plexuses to abdominal and pelvic viscera vascular smooth muscle of vessels that supply abdominopelvic viscera pain from abdominopelvic viscera also known as: preaortic ganglia, collateral ganglia; these ganglia include the celiac ganglion, aorticorenal ganglion, superior mesenteric ganglion and inferior mesenteric ganglion; preganglionic parasympathetic axons of vagal trunk origin pass through the preaortic ganglia but do not synapse there
white ramus communicans cell bodies located in the lateral horn gray matter of spinal cord levels T1-L2; none axons contained within white rami communicantes will synapse on postganglionic cell bodies that will ultimately innervate the skin, viscera, glands, blood vessels, etc. pain from viscera is carried back to the spinal cord through the white ramus communicans white rami communicantes connect the sympathetic chain to spinal nerves at vertebral levels T1-L2; carries preganglionic sympathetic axons
gray ramus communicans cell bodies located in the sympathetic chain ganglia none carries postganglionic sympathetic axons to the spinal nerve; spinal nerve will carry those axons peripherally to the skin, blood vessels, etc. none gray rami communicantes connect the sympathetic chain to spinal nerves at all vertebral levels


Some of the material presented in these tables is contained in the book:
MedCharts Anatomy by Thomas R. Gest and Jaye Schlesinger
Published by ILOC, Inc., New York. Copyright 1995.

Content of tables edited for use in this course by Patrick W. Tank, Ph.D.
Copyright 2005, Department of Neurobiology and Developomental Sciences, University of Arkansas for Medical Sciences.

Unauthorized use is prohibited.