Download SOMATIC NERVOUS SYSTEM Composed of somatic parts of CNS

SOMATIC NERVOUS SYSTEM
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Composed of somatic parts of CNS/PNS
Provides sensory and motor innervation to all parts of the body except the viscera in the body cavities,
smooth muscle, glands
SOMATIC SENSORY SYSTEM
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Transmits sensations of touch, pain, temperature, positions from sensory receptors
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Most reach conscious levels—we are aware of them
SOMATIC MOTOR SYSTEM
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Innervates only skeletal muscle—voluntary and reflexive movement
SINGLE NEURON PATHWAY from CNS to effector organ
AUTONOMIC NERVOUS SYSTEM
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Motor fibers that stimulate smooth muscle, modified cardiac muscle, and glandular cells
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Involuntary
Visceral efferent fibers of the ANS are accompanied by visceral afferent fibers
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Visceral afferents play a role in regulation of visceral function
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VISCERAL EFFERENTS
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Involves a series of TWO MULTIPOLAR NEURONS
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Presynaptic (preganglionic neuron) is located in the gray matter of the CNS
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Cell body of the postsynaptic/postganglionic neuron is located in autonomic
ganglia that synapse with smooth muscle, cardiac muscle, or glands
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Organized into
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SYMPATHETIC (thoracolumbar)
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Presynaptic cell bodies are found in the INTERMEDIOLATERAL CELL
COLUMNS (IMLs) or nuclei of the spinal cord
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Paired right and left IMLs are a part of the gray matter of T1L2/3
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Are motor fibers—axons leave the spinal cord through ventral
roots and enter the ventral rami of spinal nerves T1-L2/L3
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Pass to the sympathetic chains through white rami
communicantes
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Then they follow one of 4 possible courses:
1. Go up in the sympathetic chain to synapse with a
postsynaptic neuron of a higher paravertebral
ganglion
2. Go down the sympathetic trunk to synapse with a
postsynaptic neuron of a lower paravertebral
ganglion
3. Enter and synapse immediately with a postsynaptic
neuron of the paravertebral ganglion at that level
4. Pass through the sympathetic trunk without
synapsing with anything and go through a splanchnic
nerve to get to prevertebral ganglia
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Splanchnics innervate the abdominopelvic
viscera
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PRESYNAPTIC SYMPATHETIC FIBERS that
innervate head, neck, body wall, limbs, and
thoracic cavity follow one of the COURSES
1-3 and synapse with PARAVERTEBRAL
GANGLIA
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PRESYNAPTIC SYMPATHETIC FIBERS that
innervate viscera within the abdominopelvic
cavity follow COURSE 4
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When the postsynaptic neuron exits, it goes
back to ventral rami as gray matter—both
dorsally and ventrally
Postsynaptic cell bodies are found in
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Paravertebral ganglia
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Linked to form right and left sympathetic chains on
either side of the vertebral column—extend the
length of the column
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SUPERIOR PARAVERTEBRAL GANGLION—superior
cervical ganglion of each sympathetic trunk is
located at the base of the cranium
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GANGLION IMPAR—forms inferiorly where the two
chains unite at the level of the coccyx
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Prevertebral ganglia
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Are in the plexuses that surround the origins of the
main branches of the abdominal aorta
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CELIAC GANGLIA—surround the celiac trunk from
the abdominal aorta.
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Greatly outnumber the presynaptic fibers within the
paravertebral ganglia
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POST SYNAPTIC SYMPATHETIC FIBERS destined for the neck,
body wall, and limbs pass from paravertebral ganglia to
anterior rami of spinal nerves through GRAY RAMI
COMMUNICANTES
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So they enter all 31 pairs of spinal nerves this way,
including the posterior rami
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WHAT THEY DO:
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Contraction of blood vessels and arrector pili
muscles, cause sweating, dilate the iris
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The ones that do this in the head and neck are
located in the superior cervical ganglion, and they
either go by way of arteries or contact and run with
cranial nerves to find their destination in the head.
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THE WEIRD ONES: SPLANCHNIC NERVES convey visceral efferent
(autonomic) afferent fibers to and from the viscera of the body cavities
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CARDIOPULMONARY SPLANCHNIC NERVES (postsynaptic—go
to viscera of thoracic cavity and synapse with cardiac,
pulmonary, and esophageal plexuses
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GREATER, LESSER, LEAST THORACIC, AND LUMBAR
SPLANCHNICS
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ALL presynaptic sympathetic fibers of the abdominopelvic
splanchnics, except those involved in innervating the adrenal
glands, synapse in prevertebral ganglia
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Postsynaptic fibers from these ganglia form
periarterial plexuses, which follow branches of the
abdominal aorta to reach their destination
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Presynaptic sympathetic fibers pass through the
celiac prevertebral ganglia without synapsing and
terminate directly on the adrenal gland medulla
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These medulla cells are really postsynaptic
neurons that release their neurotransmitters
into the bloodstream—producing
WIDESPREAD SYMPATHETIC RESPONSE
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SYMPATHETICS ARE EVERYWHERE—EXCEPT CARTILAGE, NAILS, AND
HAIR
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ALL THE GANGLIA ARE AT THE MIDLINE, SO POSTSYNAPTIC
FIBERS ARE LONG, WHILE PRESYNAPTICS ARE PRETTY
SHORT.
PARASYMPATHETIC (craniosacral)
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PRESYNAPTIC CELL BODIES ARE LOCATED IN:
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Gray matter of the brainstem—fibers exit within cranial
nerves III, VII, IX, X—THIS IS THE CRANIAL
PARASYMPATHETIC OUTFLOW
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HEAD
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CN X also does thoracic and abdominal viscera
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Esophagus through left colic flexure of the
large intestine
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Gray matter of the sacral segments of the spinal cord (S2S4); fibers exit CNS through the ventral roots of sacral spinal
nerves S2-S4 and pelvic splanchnic nerves that arise from
their ventral rami; these are the SACRAL PARASYMPATHETIC
OUTFLOW
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PELVIC VISCERA
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Descending and sigmoid colon and rectum
Parasympathetic division goes only to the head, visceral cavities of the
trunk, and erectile tissues of the external genitalia
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FUNCTIONS OF THE ANS
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Sympathetic system is catabolic
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Parasympathetic is anabolic/homeostatic
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Primary function of the sympathetic is to regulate blood vessels
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Vasoconstriction
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In certain regions, they are vasodilatory—coronary vessels, skeletal muscles,
external genitals\
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VISCERAL SENSATION
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These provide info about the body’s internal environment
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MOST VISCERAL PAIN IMPULSES TRAVEL CENTRALLY ALONG VISCERAL
AFFERENT FIBERS ACCOMPANYING SYMPATHETIC FIBERS.
EXTRA INFO—SEE TABLE PAGE 65.
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Anatomic distinction between these is based on
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Location of presynaptic cell bodies
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Which nerves conduct the presynaptic fibers from the CNS
Pharmacological importance—postsynaptic neurons of the two divisions release
different neurotransmitters
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Norepi by sympathetic
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Except for sweat glands—Acetylcholine
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Acetylcholine by parasympathetic