1 nervous system subdivisions. 2 11.6: peripheral nervous system cranial nerves arising from the...
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Nervous System Subdivisions
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11.6: Peripheral Nervous System
• Cranial nerves arising from the brain• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera
• Spinal nerves arising from the spinal cord• Somatic fibers connecting to the skin and skeletal muscles• Autonomic fibers connecting to viscera
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Nerve and Nerve Fiber Classification
• Sensory nerves• Conduct impulses into brain or spinal cord
• Motor nerves• Conduct impulses to muscles or glands
• Mixed (both sensory and motor) nerves• Contain both sensory nerve fibers and motor nerve fibers• Most nerves are mixed nerves• ALL spinal nerves are mixed nerves (except the first pair)
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Nerve Fiber Classification
• General somatic efferent (GSE) fibers• Carry motor impulses from CNS to
skeletal muscles• Stimulate the muscles to contract
• General visceral efferent (GVE) fibers• Carry motor impulses away from CNS
to smooth muscles and glands
• General somatic afferent (GSA) fibers• Carry sensory impulses to CNS from
skin and skeletal muscles
• General visceral afferent (GVA) fibers• Carry sensory impulses to CNS from
blood vessels and internal organs
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Nerve Fiber Classification
• Special somatic efferent (SSE) fibers• Carry motor impulses from brain to muscles used in chewing,
swallowing, speaking and forming facial expressions
• Special visceral afferent (SVA) fibers• Carry sensory impulses to brain from olfactory and taste receptors
• Special somatic afferent (SSA) fibers• Carry sensory impulses to brain from receptors of sight, hearing and
equilibrium
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Cranial Nerves
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Olfactory bulb
Hypoglossal (XII)
Optic tract
Olfactory tract
Olfactory (I)
Optic (II)
Oculomotor (III)
Abducens (VI)
Facial (VII)
Glossopharyngeal (IX)
Accessory (XI)
Trochlear (IV)
Trigeminal (V)
Vestibulocochlear (VIII)
Vagus (X)
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Functions of Cranial Nerves
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Spinal Nerves
• ALL are mixed nerves (except the first pair)• 31 pairs of spinal nerves:
• 8 cervical nerves• (C1 to C8)
• 12 thoracic nerves• (T1 to T12)
• 5 lumbar nerves• (L1 to L5)
• 5 sacral nerves• (S1 to S5)
• 1 coccygeal nerve• (Co or Cc)
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Cauda equina
C1C2C3C4C5C6C7C8T1T2
T3
T4
T5
T6
T7
T8
T9
T10T11
T12
L1
L2
L3L4
L5
S2S3
S4
S1
S5Co
Posteriorview
Cervicalnerves
Thoracicnerves
Lumbarnerves
Sacralnerves
Coccygealnerve
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Spinal Nerves
• Dorsal root (aka posterior root)
• Sensory root• Axons of sensory
neurons are in the dorsal root ganglion
• Dorsal root ganglion • Aka DRG• Cell bodies of sensory
neurons whose axons conduct impulses inward from peripheral body parts
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Lateral horn
Ventral root(a)
(b)
Dorsal root
Dorsal root
Spinal nerve
Dorsal rootganglion
Posteriormedian sulcus
Posteriorhorn
Anteriorhorn
Centralcanal
Anteriormedianfissure
Dorsal branchof spinal nerveVentral branchof spinal nerve
Visceral branchof spinal nerve
Paravertebralganglion
Ventral branchof spinal nerve (ventral ramus)
Dorsal branchof spinal nerve (dorsal ramus)
Paravertebralganglion
Visceral branchof spinal nerve
Ventral root
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Spinal Nerves
• Ventral root (aka anterior root) • Motor root• Axons of motor neurons
whose cell bodies are in the spinal cord in the gray matter
• Supplies nerves to muscles and skin on the front & sides of the trunk & limbs
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Lateral horn
Ventral root(a)
(b)
Dorsal root
Dorsal root
Spinal nerve
Dorsal rootganglion
Posteriormedian sulcus
Posteriorhorn
Anteriorhorn
Centralcanal
Anteriormedianfissure
Dorsal branchof spinal nerveVentral branchof spinal nerve
Visceral branchof spinal nerve
Paravertebralganglion
Ventral branchof spinal nerve (ventral ramus)
Dorsal branchof spinal nerve (dorsal ramus)
Paravertebralganglion
Visceral branchof spinal nerve
Ventral root
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Spinal Nerves
• Spinal nerve• Union of ventral root
and dorsal roots• Hence we now have a
“mixed” nerve• A posterior branch of a
spinal nerve supplies the muscles and skin of the back
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Lateral horn
Ventral root(a)
(b)
Dorsal root
Dorsal root
Spinal nerve
Dorsal rootganglion
Posteriormedian sulcus
Posteriorhorn
Anteriorhorn
Centralcanal
Anteriormedianfissure
Dorsal branchof spinal nerveVentral branchof spinal nerve
Visceral branchof spinal nerve
Paravertebralganglion
Ventral branchof spinal nerve (ventral ramus)
Dorsal branchof spinal nerve (dorsal ramus)
Paravertebralganglion
Visceral branchof spinal nerve
Ventral root
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Plexuses
C1C2C3C4C5C6C7C8T1
T2T3
T4
T5
T6
T8
T9
T10T11
T12
L1
L2
L3
L4
L5
S2S3S4S5
Co
Posterior view
Cervical plexus(C1–C4)
Lumbosacral plexus(T12–S5)
Sciatic nerve
Brachial plexus(C5–T1)
Obturator nerve
Phrenic nerve
Ulnar nerveMedian nerveRadial nerveAxillary nerve
T7
S1
Cauda equina
Musculocutaneousnerve
Femoralnerve
Intercostalnerves
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Nerve Plexuses
• Nerve plexus• Complex networks formed by anterior branches (ventral rami) of spinal
nerves• The fibers of various spinal nerves are sorted and recombined• There are three (3) nerve plexuses:
• (1) Cervical plexus• Formed by anterior branches of C1-C4 spinal nerves• Lies deep in the neck on either side.• Fibers supply the muscles and skin of the neck
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Brachial Plexus• (2) Brachial plexus
• Formed by anterior branches C5-T1• Lies deep within shoulders between the
neck and axilliae• There are five (5) branches:• 1. Musculocutaneous nerve
• Supply muscles of anterior arms and skin of forearms
• 2. Ulnar and 3. Median nerves• Supply muscles of forearms and
hands• Supply skin of hands
• 4. Radial nerve• Supply posterior muscles of arms
and skin of forearms and hands• 5. Axillary nerve
• Supply muscles and skin of superior, lateral, and posterior arms
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Musculocutaneous n.
Musculocutaneous n.
Humerus
Thoracodorsal n.
Lower subscapular n.
Suprascapular n.
Lateral pectoral n.
Medial pectoral n.
Axillary n.
Axillary n.
Radial n.
Radial n.
Radius
Ulna
Ulnar n.
Ulnar n.
Median n.Median n.
C5
C5
C6
C6
C7
C7
C8
C8
T1
T1
(a)
(b)
Ventral rami: C5, C6, C7, C8, T1
Anterior divisions
Posterior divisions
Trunks: upper, middle, lower
Dorsalscapular n.
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Lumbosacral Plexus• (3) Lumbosacral plexus
• Formed by the anterior branches of L1-S5 roots
• Can be a lumbar (L1-L5) plexus and a sacral (S1-S5) plexus
• Extends from lumbar region into pelvic cavity
• Obturator nerve • Supply motor impulses to
adductors of thighs• Femoral nerve
• Supply motor impulses to muscles of anterior thigh and sensory impulses from skin of thighs and legs
• Sciatic nerve• Supply muscles and skin of
thighs, legs and feet
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Sciatic n.
Saphenous n.
Femoral n.
Obturator n.
Tibial n.
Pudendal n.
(b) (c)(a)
Femoral n.
Obturator n.
Pudendal n.
Sciatic n.
L1
L2
L3
L4
L5
S1
S2
S3
S4
S5
Ventralrami
Anteriordivisions
Posteriordivisions
Lateralfemoralcutaneous n.
Superiorgluteal n.
Inferiorgluteal n.
Superiorgluteal n.
Inferiorgluteal n.
Sacralplexus
Common fibular(peroneal) n.
Posteriorcutaneous n.
Commonfibular(peroneal) n.Tibial n.
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11.7: Autonomic Nervous System
• Functions without conscious effort• Controls visceral activities• Regulates smooth muscle, cardiac muscle, and glands• Efferent fibers typically lead to ganglia outside of the CNS
• Two autonomic divisions regulate:• Sympathetic division (speeds up)
• Prepares body for ‘fight or flight’ situations• Parasympathetic division (slows down)
• Prepares body for ‘resting and digesting’ activities