G03 - ANS, CNS, PNS
Dr. Morton
G03: ANS, CNS, PNS
Reading: GAFS 62-88
Objectives:
•Familiarize students with the structure and organization of the nervous system
Nervous System Definitions and Overview
•Structural Divisions
• Central nervous system (CNS)- the portion of the nervous system consisting
of the brain and spinal cord. Command center that integrates and processes
nervous system information.
• Peripheral nervous system (PNS)- the part of the vertebrate nervous system
constituting the nerves outside the central nervous system (nerves and ganglia)
• Upper motor neuron (UPN)- a motor neuron whose cell body is located in the
motor area of the cerebral cortex and whose processes connect with motor
nuclei in the brainstem or the anterior horn of the spinal cord.
• Lower motor neuron (LMN)- a motor neuron whose cell body is located in the
brainstem or the spinal cord and whose axon innervates skeletal muscle fibers. Also called final motor neuron.
• Functional Divisions
• Sensory (afferent = back to the CNS)
• General afferent (touch, temperature, pain, etc)
• Visceral afferent (viscera = internal organ)
• Special afferent (sight, taste, sound)
• Motor (efferent= away from the CNS)
• Somatic efferent- innervates skeletal muscles derived from somites
(body wall)
• Branchial efferent- innervates skeletal muscles derived from the pharyngeal arches
• Visceral efferent (viscera = internal organ)
•Functional Organization
•Receive stimuli
•Receptors (e.g., pain, temperature)
•Transmit responses
•Conductors (e.g., muscle contraction)
•Process input
•Brain (interpretation)
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G03 - ANS, CNS, PNS
CNS
PNS
Sensory
General
Afferent
Visceral
Afferent
Motor
Special
Afferent
Somatic
Efferent
Skeletal muscle of the body
wall
Touch
Pain
Temperature
Vibration
Proprioception
Return information
(reflexes, pain) concerning hollow organs and blood vessels
Sight,
Taste,
Sound
Branchial
Efferent
Visceral
Efferent
Skeletal muscle derived
from pharyngeal arches
Smooth muscle, glands,
and modified
cardiac muscle
Sympathetic
T1-L2
Parasympathetic
CN 3,7,9,10
S2-S4
Organ, Tract, or System
Sympathetic
Parasympathetic
Pupil
•Dilates
•Constricts
Skin
•Arrector pili muscle contraction
•Vessels- vasoconstriction
•Sweat glands- sweating
•No effect
Lacrimal and salivary glands
•Decreases secretion
•Increase secretion
Heart
•↑ rate and strength of contraction
•Dilates coronary vessels
•↓ rate and strength of contraction
•Constricts coronary vessels
Lung
•Bronchodilation
•Bronchoconstriction
Digestive tract
•Inhibits peristalsis
•Constricts blood vessels
•Stimulates peristalsis
Genital system
•Ejaculation
•Erection
Suprarenal medulla
•Release of adrenaline
•No effect
Overview
•Fight or Flight (E)
•Exercise
•Excitement
•Emergency
•Rest and Digest (D)
•Digestion
•Defecation
•Diuresis
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G03 - ANS, CNS, PNS
CNS
•Organization
•Brain and spinal cord
•Gray matter
•Contains nerve cells
•White matter
•Contains nerve fibers
•Meninges (membranes)
•Dura mater (dur = tough, mater =
mother)
•Arachnoid mater (arachnoid = spider, i.e., spider web-like)
•Pia mater
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G03 - ANS, CNS, PNS
CNS (continued)
•Spinal Cord
•Located in the vertebral column (spinal canal)
•Length
•Embryo: fills the column length
•At birth: extends caudally to L2 - L3
•Adult: extends caudally to L1 - L2
•Why is this distinction clinically important?
•Enlargements (2)
•Cervical (upper limbs)
•Lumbar (lower limbs)
Regions of the Spinal Cord and Verterbral Column
Region
Number of Spinal
Nerves
Number of Vertebrae
Cervical
8
7
Thoracic
12
12
Lumbar
5
5
Sacral
5
5
Coccygeal
1
4
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G03 - ANS, CNS, PNS
CNS (continued)
•Spinal cord components
•Dentate (denticulate) ligaments
•Conus medullaris
•Cauda equina
•Filum terminale
PNS
•Organization
•Ganglia (cell bodies)
•Sensory
•Dorsal root ganglia
•Cranial nerve ganglia
•Nerves (fibers)
•Sensory and motor
•Peripheral nerves (31 pairs)
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G03 - ANS, CNS, PNS
PNS (continued)
•Typical Spinal Nerve and Its Peripheral Distribution
•Components
•Dorsal roots (sensory)
•Cell bodies located in the dorsal root ganglia
•Ventral roots (motor)
•Cell bodies located in the CNS
•Formed by fusion of segmental ventral and dorsal roots (2-4 mm
long)
•Exit intervertebral foramen
•Divide into dorsal and ventral primary rami
•Plexuses
•Cervical (neck)
•Brachial (upper limb)
•Lumbar (distal thoracic region, abdomen, pelvis and lower limb)
•Sacral (pelvis and lower limb)
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G03 - ANS, CNS, PNS
Pathways
• Somatic afferent (sensory)
• Sensory fibers carry sensor
(afferent information from
the tissues of the limbs and
back through the ventral
and dorsal rami respectively, to the dorsal root to
the spinal cord (Note: the
collection of sensory cell
bodies in the dorsal root
forming the dorsal root ganglion (DRG))
•
Somatic efferent (motor)
• Motor neurons carry somatic motor information
from the spinal cord to the
skeletal muscles of the
limbs and back
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G03 - ANS, CNS, PNS
Sympathetic system
• “Thoracolumbar” nervous system
• T1 to L2
• Function: fight, fright, flight
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G03 - ANS, CNS, PNS
• Visceral efferents (sympathetic)
• Preganglionic fibers from
spinal levels T1-L2 course
out the ventral root and exit
the spinal nerve through a
white rami communicantes
to synapse in the paravertebral ganglion
• Postganglionic sympathetic
neurons exit through a gray
rami communicantes to
course to the blood vessels,
erector pili muscles and
sweat glands of the upper
and lower limbs
•
Visceral efferents (sympathetics)
• Preganglionic fibers from spinal
levels T1-L2 course out the ventral root and exit the spinal nerve
through a white rami communicantes to synapse in a higher or
lower paravertebral ganglion
• Postganglionic sympathetic neurons exit through a gray rami
communicantes to course to the
blood vessels, erector pili muscles and sweat glands of the upper and lower limbs
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G03 - ANS, CNS, PNS
•
Visceral efferents (sympathetics)
• Preganglionic fibers course through a splanchnic nerve to synapse in a
pre-vertebral ganglion (i.e. celiac ganglion)
• Postganglionic fibers go to intestines, kidneys, liver, pancreas, etc.
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G03 - ANS, CNS, PNS
•
Visceral efferents
(sympathetics)
• Preganglionic fibers from
spinal levels T1-T4 course
up the sympathetic trunk to
synapse in a more superior
sympathetic ganglion (i.e.
superior cervical ganglion)
• Postganglionic fibers go
from superior sympathetic
ganglion go to heart, lung,
eye, lacrimal gland, salivary
glands, cranial vessels
•
Visceral efferents
(sympathetics)
• Preganglionic fibers from
spinal levels T12-L2 course
down the sympathetic trunk
to synapse in a more inferior sympathetic ganglion
(inferior mesenteric)
• Postganglionic fibers go to
colon, rectum, and genitalia
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G03 - ANS, CNS, PNS
•
Visceral afferents (on sympathetic fibers)
• Return information from internal organs and smooth muscle of large blood
vessel walls in the limbs
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G03 - ANS, CNS, PNS
Parasympathetic system
• “Cranio-caudal” nervous system
• Cranial nerves 3, 7, 9, 10; S2-S4
• Function: homeostasis
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G03 - ANS, CNS, PNS
Comparison of Pre- versus Postganglionic Neurons of the ANS
Sympathetic
Parasympathetic
Short preganglionic fibers
Long preganglionic fibers
Long postganglionic fibers
Short postganglionic fibers
Ganglia located relatively far
from their target organ
Ganglia located on or near their
target organ
Sympathetic
Parasympathetic
Preganglionic cell bodies: T1
to L2
Preganglionic cell bodies:
brainstem and S2-S4
Postganglionic cell bodies:
chain or collateral ganglia
Postganglionic cell bodies:
cranial or enteric ganglia
Ganglia run entire length of
spinal cord
Ganglia are at one end or the
other of spinal cord
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