Transcript Spinal Nerves

PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
13
The Peripheral
Nervous
System and
Reflex Activity:
Part C
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Spinal Nerves
• 31 pairs of mixed nerves named according to
their point of issue from the spinal cord
• 8 cervical (C1–C8)
• 12 thoracic (T1–T12)
• 5 Lumbar (L1–L5)
• 5 Sacral (S1–S5)
• 1 Coccygeal (C0)
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Cervical plexus
Brachial plexus
Cervical
enlargement
Intercostal
nerves
Cervical
nerves
C1 – C8
Thoracic
nerves
T1 – T12
Lumbar
enlargement
Lumbar plexus
Sacral plexus
Cauda equina
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Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Figure 13.6
Spinal Nerves: Roots
• Each spinal nerve connects to the spinal cord
via two roots
• Ventral roots
• Contain motor (efferent) fibers from the
ventral horn motor neurons
• Fibers innervate skeletal muscles
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Spinal Nerves: Roots
• Dorsal roots
• Contain sensory (afferent) fibers from sensory
neurons in the dorsal root ganglia
• Conduct impulses from peripheral receptors
• Dorsal and ventral roots unite to form spinal
nerves, which then emerge from the vertebral
column via the intervertebral foramina
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Gray matter
White matter
Ventral root
Dorsal root
Dorsal root
ganglion
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Spinal nerve
Dorsal and
ventral rootlets
of spinal nerve
Rami communicantes
Sympathetic trunk
ganglion
Anterior view showing spinal cord, associated nerves, and vertebrae.
The dorsal and ventral roots arise medially as rootlets and join
laterally to form the spinal nerve.
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Figure 13.7 (a)
Spinal Nerves: Rami
• Each spinal nerve branches into mixed rami
• Dorsal ramus
• Larger ventral ramus
• Meningeal branch
• Rami communicantes (autonomic pathways)
join to the ventral rami in the thoracic region
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Spinal Nerves: Rami
• All ventral rami except T2–T12 form interlacing
nerve networks called plexuses (cervical,
brachial, lumbar, and sacral)
• The back is innervated by dorsal rami via
several branches
• Ventral rami of T2–T12 as intercostal nerves
supply muscles of the ribs, anterolateral
thorax, and abdominal wall
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Dorsal ramus
Ventral ramus
Spinal nerve
Rami communicantes
Sympathetic trunk
ganglion
Intercostal nerve
Dorsal root
ganglion
Dorsal root
Ventral root
Branches of intercostal
nerve
• Lateral cutaneous
• Anterior cutaneous
Sternum
(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
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Figure 13.7 (b)
Cervical Plexus
• Formed by ventral rami of C1–C4
• Innervates skin and muscles of the neck, ear,
back of head, and shoulders
• Phrenic nerve
• Major motor and sensory nerve of the
diaphragm (receives fibers from C3–C5)
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Brachial Plexus
• Formed by ventral rami of C5–C8 and T1 (and often
C4 and T2)
• It gives rise to the nerves that innervate the upper
limb
• Major branches of this plexus:
• Roots—five ventral rami (C5–T1)
• Trunks—upper, middle, and lower
• Divisions—anterior and posterior
• Cords—lateral, medial, and posterior
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Brachial Plexus: Nerves
• Axillary—innervates the deltoid, teres minor, and skin
and joint capsule of the shoulder
• Musculocutaneous—innervates the biceps brachii
and brachialis and skin of lateral forearm
• Median—innervates the skin, most flexors and
pronators in the forearm, and some intrinsic muscles
of the hand
• Ulnar—supplies the flexor carpi ulnaris, part of the
flexor digitorum profundus, most intrinsic muscles of
the hand, and skin of medial aspect of hand
• Radial—innervates essentially all extensor muscles,
supinators, and posterior skin of limb
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Lumbar Plexus
• Arises from L1–L4
• Innervates the thigh, abdominal wall, and
psoas muscle
• Femoral nerve—innervates quadriceps and
skin of anterior thigh and medial surface of leg
• Obturator nerve—passes through obturator
foramen to innervate adductor muscles
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Ventral rami
Iliohypogastric
Ilioinguinal
Genitofemoral
Lateral femoral
cutaneous
Obturator
Femoral
Lumbosacral
trunk
Ventral
rami:
Iliohypogastric
L1
Ilioinguinal
Femoral
Lateral femoral
L2
cutaneous
Obturator
L3
Anterior femoral
cutaneous
Saphenous
L4
L5
(a) Ventral rami and major branches
of the lumbar plexus
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
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Figure 13.10
Sacral Plexus
• Arises from L4–S4
• Serves the buttock, lower limb, pelvic structures,
and perineum
• Sciatic nerve
• Longest and thickest nerve of the body
• Innervates the hamstring muscles, adductor magnus,
and most muscles in the leg and foot
• Composed of two nerves: tibial and common fibular
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Ventral rami
Ventral rami:
L4
Superior
gluteal
Lumbosacral
trunk
Inferior
gluteal
Common
fibular
Tibial
Posterior
femoral
cutaneous
Pudendal
Sciatic
L5
S1
S2
S3
S4
S5
Co1
Ventral rami and major branches
of the sacral plexus
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Figure 13.11 (a)
Superior gluteal
Inferior gluteal
Pudendal
Sciatic
Posterior femoral
cutaneous
Common fibular
Tibial
Sural (cut)
Deep fibular
Superficial fibular
Plantar branches
(b) Distribution of the major nerves from
the sacral plexus to the lower limb
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Figure 13.11 (b)
Innervation of Skin
• Dermatome: the area of skin innervated by
the cutaneous branches of a single spinal
nerve
• All spinal nerves except C1 participate in
dermatomes
• Most dermatomes overlap, so destruction of a
single spinal nerve will not cause complete
numbness
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Innervation of Joints
• Hilton’s law: Any nerve serving a muscle that
produces movement at a joint also innervates
the joint and the skin over the joint
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