Peripheral Nervous System Cranial nerves and spinal nerves 35/pdf lecture/a35 peripheral...
Transcript of Peripheral Nervous System Cranial nerves and spinal nerves 35/pdf lecture/a35 peripheral...
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Peripheral Nervous SystemPeripheral Nervous SystemCranial nerves and spinal nervesCranial nerves and spinal nerves
Dr. Carmen E. Dr. Carmen E. RexachRexachAnatomy 35Anatomy 35
Mt San Antonio CollegeMt San Antonio College
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Cranial Nerves• 12 pairs
– arise from the inferior aspect of the brain
– 2 from the forebrain– 10 from the brain stem
• Functions– Sensory– Motor– ….or both
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I.OhII.OhIII.OhIV. To V. Touch VI. And VII. FeelVIII. VeryIX. GoodX. VelvetXI. AXII.H
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Roots• axon fibers passing directly to and from the
spinal cord• pure sensory or motor• posterior = sensory• anterior = motor
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ganglia
• Posterior Root Ganglia (dorsal root ganglia) contain cell bodies of sensory neurons
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Spinal Nerves• Connect CNS to muscles,
glands, receptors• Anterior rootlets from
spinal cord form anterior root (motor)
• Posterior rootlets from spinal cord form posterior root (sensory)
• Anterior and posterior roots merge to form mixed spinal nerves
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Spinal nerves
• 31 pairs• Pass through the
intervertebral foramina– 8 pairs Cervical– 12 pairs Thoracic– 5 pairs Lumbar– 5 pairs Sacral– 1 pairs Coccygeal
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Branches of spinal nerves• Nerves split after passing through intervertebral
foramina• Branches are called rami (s, ramus)• Anterior (ventral) rami form several branches and
innervate anterior, lateral trunk, upper & lower limbs– Some form nerve plexus
• Posterior (dorsal) rami split into 2 branches innervating deep muscles and skin of back
• Rami communicantes– Associated with spinal nerves– Part of autonomic nervous system
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Rami
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PLEXUS:regions where spinal nerves merge and rebranch
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Sites of injection of local anesthetics
• Spinal nerve block– Into subarachnoid space in spinal canal
• Paravertebral nerve block• Epidural or peridural nerve block• Caudal block
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Epidural space• Surrounds dural sac• Contains areolar CT,
fat, lymphatics, arteries, nerve plexus and spinal nerve roots
• Boundaries– Anterior = posterior
longitudinal ligament– Posterior = ligamentum
flavum and periosteumof the laminae
– Lateral = pedicles of spinal column and intervertebral foramina
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Epidural in childbirth• 16-19G needle is inserted into
the epidural space in lumbar region
• Epidural catheter is attached• Anesthetic infused into
epidural space– Pregnancy increases
susceptibility to local anesthetic toxicity
– Commonly used anesthetics include:
• Bupivicaine (g, Marcaine)• Ropivicaine (g, Naropin)• Levobupivicaine (g, Chirocaine)
Note: There is currently no safe way of introducing anesthetic through a tattoo. Therefore, those with lower back tattoos cannot have an epidural.
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A Reflex Arc:• Control on a local level• anatomical and functional connection
between sensory and motor activities• Examples:
– Patellar reflex– Flexor reflex– Crossed extensor reflex
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Reflex arc
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Patellar reflex
• Monosynaptic• Ipsilateral• Monosegmental
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Flexor reflex
• Multisynaptic• Ipsilateral• Multisegmental
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Crossed extensor reflex
• Multisynaptic• Contralateral• Multisegmental
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OrganizationCNS PNS
somatic autonomic
sympathetic parasympathetic
sensory motor
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The Autonomic Nervous System:• “involuntary”• function to modulate ongoing automatic
activities• target tissues
– smooth muscle– cardiac muscle– glands
• Examples:– heart rate– ventilation– digestive tract activity
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ANS is two neuron system
Preganglionic neuron
Postganglionic neuron
1
2
CNS
PNS
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Autonomic nervous system
• preganglionic fibers– exit the CNS and terminate onto
autonomic ganglia• postganglionic fibers
– exit the autonomic ganglia and terminate onto the target
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Sympathetic division
(thoracolumbar)• Sympathetic chain• preganglionic
fibers synapse on postganglionic fibers very close to the CNS and far away from effector organs
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Sympathetic division
• Sympathetic chain– Aka: paravertebral ganglia or lateral ganglia– Location: either side of vertebral column– Innervate effectors in body wall, inside thoracic
cavity• Collateral ganglia
– Aka: prevertebral ganglia– Location: between sympathetic chain and organ– Innervate tissues & organs of abdominopelvic
cavity• Adrenal medulla
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Collateral ganglia
• Celiac ganglion– Stomach, duodenum, liver,
pancreas, spleen, gallbladder
• Superior mesenteric ganglion– Small intestines, beginning
of large intestines• Inferior mesenteric
ganglion– Kidney, bladder,
reproductive organs, large intestines
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Adrenal medulla
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Adrenal medulla• Sympathetic preganglionic neurons enter
adrenal medulla and stimulate postganglionic neurons
• Chromaffin cells respond and release adrenalin (80% epinephrine, 20% norepinephrine)– Cells are derived from neural crest tissue
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parasympathetic (craniosacral)
• “rest and repose”• involves cranial nerves: III, VII, IX and X• preganglionic fibers extend from the CNS
to the target• Terminal ganglia located within the target
organ• postganglionic fibers
– Short– within the target organ
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Visceral reflexes• Polysynaptic• Can be modified by higher centers• Examples
– Parasympathetic• Consensual light reflex• Swallowing reflex
– Sympathetic• Pupillary reflex• Vasomotor reflexes