AUTONOMIC NERVOUS SYSTEM
(SYMPATHETIC PART)
LEARNING OBJECTIVES
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Define Autonomic nervous system.
Define sympathetic part of ANS.
Compare somatic and autonomic systems.
Recognize the components of sympathetic part of nervous system (thoracolumbar
outflow: lateral gray horn, paravertebral sympathetic chain, prevertebral ganglia
and plexuses).
Differentiate between white and gray rami communicans.
Describe the different fates (destination) of white and gray rami (preganglionic
and post ganglionic fibres).
List the functions.
AUTONOMIC NERVOUS SYSTEM
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The portion of the nervous system that controls
most of visceral functions of the body and is called the autonomic nervous system.
• Helps to control arterial pressure, gastrointestinal motility, gastrointestinal
secretions, urinary bladder emptying, sweating, body temperature, and many
other activities
• Some of the above functions are controlled almost entirely and some only
partially by the autonomic nervous system.
SYMPATHETIC NERVOUS SYSTEM
• Sympathetic part of autonomic nervous system prepares the body
for emergency.
• Sympathetic system consists of efferent outflow from
spinal cord, to ganglionated sympathetic trunks,
important branches, plexus and regional ganglia
COMPARISON OF AUTONOMIC AND
SOMATIC MOTOR SYSTEMS
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Somatic motor system
-One motor neuron extends from the CNS to skeletal muscle
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-Axons are well myelinated, conduct impulses rapidly
Autonomic nervous system
– Chain of two motor neurons
• Preganglionic neuron
• Postganglionic neuron
– Conduction is slower due to thinly or unmyelinated axons
COMPARISON OF SYMPATHETIC
AND PARASYMPATHETIC DIVISIONS
ANATOMICAL DIFFERENCES IN SYMPATHETIC
AND PARASYMPATHETIC DIVISIONS
• Arise from different regions of the CNS
– Sympathetic
also called the thoracolumbar division
– Parasympathetic
also called the craniosacral division
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Length of postganglionic fibers
– Sympathetic – long postganglionic
fibers
– Parasympathetic – short postganglionic
fibers.
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Branching of axons
– Sympathetic axons – highly branched
• Influences many organs
– Parasympathetic axons – few branches
• Localized effect.
NEUROTRANSMITTERS OF AUTONOMIC NERVOUS SYSTEM
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Neurotransmitter released by preganglionic axons:
– Acetylcholine for both branches (cholinergic)
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Neurotransmitter released by postganglionic axons:
– Sympathetic – most release NOREPINEPHRINE (adrenergic).
– Parasympathetic – release ACETYLCHOLINE
GENERAL ORGANIZATION OF THE PERIPHERAL PORTIONS OF
SYMPATHETIC NERVOUS SYSTEM
Shown specifically in the figure are
(1) One of the two paravertebral sympathetic chains of ganglia that are
interconnected with the spinal nerves on the side of the vertebral column,
(2) Prevertebral ganglia
(the celiac and hypogastric), and
(3) Nerves extending from the ganglia to the different internal
organs.
ORGANIZATION AND ANATOMY
OF THE SYMPATHETIC DIVISION
• Much more complex than the parasympathetic division, both
anatomically and functionally.
• Sympathetic preganglionic neuron cell bodies are housed in the lateral horn of
the T1–L2 regions of the spinal cord.
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Preganglionic sympathetic axons travel with somatic motor neuron axons to
exit the spinal cord and enter first the anterior roots and then the T1–L2 spinal
nerves.
Preganglionic sympathetic axons remain with the spinal nerve for merely a short
distance before they branch off and leave the spinal nerve.
LEFT AND RIGHTSYMPATHETIC TRUNKS OR
PARAVERTEBRAL GANGLIA
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Immediately anterior to the paired spinal nerves are the left and right sympathetic
trunks.
Each is located immediately lateral to the vertebral column.
sympathetic trunk (or paravertebral) ganglia, house sympathetic ganglionic
neuron cell bodies.
LEFT AND RIGHT SYMPATHETIC TRUNKS OR
PARAVERTEBRAL GANGLIA
• Joined to ventral rami by white
and gray rami communicantes
• One sympathetic trunk ganglion is approximately associated with each spinal
nerve.
• Fusion of ganglia  fewer ganglia
than spinal nerves
• The cervical portion of each sympathetic trunk is partitioned into only three
sympathetic trunk ganglia
—the superior, middle, and inferior cervical ganglia—as opposed to the eight
cervical spinal nerves.
WHITE RAMI
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Connecting the spinal nerves to each sympathetic trunk are rami communicantes.
Carry preganglionic sympathetic axons from the T1–L2 spinal nerves to the
sympathetic trunk.
Associated only with the T1–L2 spinal nerves.
Preganglionic axons are myelinated.
The white ramus has a whitish appearance.
GRAY RAMI
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Carry postganglionic sympathetic axons from
the sympathetic trunk to the spinal nerve.
Axons are unmyelinated gray rami have a
grayish appearance.
Connect to all spinal nerves, including the
cervical, sacral, and coccygeal spinal nerves.
Sympathetic information that started out in the
thoracolumbar region can be dispersed to all
parts of the body.
SYMPATHETIC DIVISION OF
THE ANS
SPLANCHNIC NERVES
SPLANCHNIC NERVES
• Composed of
preganglionic sympathetic
axons.
• Run anteriorly from the
sympathetic trunk to most
of the viscera.
• Larger splanchnic nerves
have specific names:
1. Greater thoracic splanchnic
nerves
2. Lesser thoracic splanchnic
nerves
3. Least thoracic splanchnic
nerves
4. Lumbar splanchnic nerves
5. Sacral splanchnic nerves
PREVERTEBRAL (OR COLLATERAL) GANGLIA
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Splanchnic nerves terminate in prevertebral (or collateral)
ganglia.
Called ―prevertebral‖ because they are immediately anterior
to the vertebral column
Unpaired, not segmentally arranged
Occur only in abdomen and pelvis
Typically cluster around the major abdominal arteries and
are named for these arteries.
Example: Celiac, superior mesenteric, inferior mesenteric,
inferior hypogastric ganglia
Sympathetic postganglionic axons extend away from the
ganglionic neuron cell bodies in these ganglia and innervate
many of the abdominal organs.
SUMMARY ; SYMPATHETIC SYSTEM
SUMMARY (continued)
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Output from preganglionic neurons in lateral horn of thoracic and upper lumbar
spinal cord (thoracolumbar outflow).
• Short preganglionic axons travel to sympathetic chain ganglia via white ramus
communicantes. Postsynaptic neuron exits via gray ramus communicantes.
• Long postganglionic axons travel to their targets via the
gray ramus communicantes.
• Some preganglionic axons travel to prevertebral ganglia via
the splanchnic nerves--are not paired
a)
Celiac ganglion
b)
Superior mesenteric ganglion
c)
Inferior mesenteric ganglion
d)
Inferior hypogastric ganglion
• Adrenal medulla
Acts like a sympathetic postganglionic neuron, but secretes epinephrine as opposed
to norepinephrine.
• Effects increase alertness, increased energy, cardiovascular & respiratory
activity, elevation of muscle tone, mobilization of energy reserves
FUNCTIONS
 Sympathetic part of autonomic nervous system prepares the body for emergency.
 Heart rate is increased.
 Arterioles of skin and intestine are constricted but the arterioles of skeletal
muscles are dilated.
 Blood pressure is raised.
 Pupils are dilated.
 It inhibits the smooth muscles of bronchi, intestine and bladder and closes the
sphincters.
 Hair is made to stand and sweating occurs.
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REFERENCES
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Clinical Neuroanatomy by Richard S. Snell
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