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G03 - ANS, CNS, PNS
26
Reading: GAFS 62-88 Objectives: •Familiarize students with the structure and organization of the nervous system
Dr. Morton
G03: ANS, CNS, PNS
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 gan-glia)
• 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 fi-bers. 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 pha-
ryngeal 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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CNS
PNS Motor Sensory
Touch Pain Temperature Vibration Proprioception
Branchial Efferent
Somatic Efferent
Visceral Efferent
Visceral Afferent
General Afferent
Special Afferent
Skeletal mus-cle of the body wall
Skeletal mus-cle derived from pharyn-geal arches
Return information (reflexes, pain) con-cerning hollow or-gans and blood ves-sels
Sight, Taste, Sound
Smooth mus-cle, 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 contrac-tion
•Dilates coronary vessels
•↓ rate and strength of contrac-tion
•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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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 = spi-
der, i.e., spider web-like) •Pia mater
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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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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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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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Pathways • Somatic afferent (sensory)
• Sensory fibers carry sensor (afferent information from the tissues of the limbs and back through the ventral and dorsal rami respec-tively, to the dorsal root to the spinal cord (Note: the collection of sensory cell bodies in the dorsal root forming the dorsal root gan-glion (DRG))
• Somatic efferent (motor) • Motor neurons carry so-
matic motor information from the spinal cord to the skeletal muscles of the limbs and back
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Sympathetic system • “Thoracolumbar” nervous system • T1 to L2 • Function: fight, fright, flight
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• 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 paraverte-bral 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 ven-tral root and exit the spinal nerve through a white rami communi-cantes to synapse in a higher or lower paravertebral ganglion
• Postganglionic sympathetic neu-rons exit through a gray rami communicantes to course to the blood vessels, erector pili mus-cles and sweat glands of the up-per and lower limbs
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• 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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• 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 infe-rior sympathetic ganglion (inferior mesenteric)
• Postganglionic fibers go to colon, rectum, and genitalia
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• 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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Parasympathetic system • “Cranio-caudal” nervous system • Cranial nerves 3, 7, 9, 10; S2-S4 • Function: homeostasis
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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