peripheral nervous system (pns) the nervous...
TRANSCRIPT
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Cranial and spinal Nerves
The Nervous System
Peripheral Nervous System (PNS)
• All neural structures outside the brain and spinal cord
– Sensory receptors
– Peripheral nerves and associated ganglia
– Motor neuron endings
– Constitutes a pathway between CNS and outlying
structures
– 12 pairs of cranial nerves
– 31 pairs of spinal nerves
Figure 13.1
Central nervous system (CNS) Peripheral nervous system (PNS)
Motor (efferent) divisionSensory (afferent)
division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
Figure 13.3b
Blood
vessels
Fascicle
Epineurium
Perineurium
Endoneurium
Axon
Myelin sheath
(b)
Cranial Nerves
• 12 pairs of nerves– Associated with the brain
• Do not decussate– May continue in tracts that do
– Typically see ipsilateral functional deficits with brain injury
• Function may be sensory, motor, or both– Most are at least partially mixed
• Each nerve is identified by…– Number (I through XII)
– Name
Figure 13.5 (a)
Frontal lobe
Temporal lobe
Infundibulum
Facial
nerve (VII)
Vestibulo-
cochlear
nerve (VIII)Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
(a)
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Optic chiasma
Optic nerve
(II)
Optic tractOculomotor
nerve (III)Trochlear
nerve (IV) Trigeminal
nerve (V) Abducens
nerve (VI)
Cerebellum
Medulla
oblongata
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Figure 13.5 (b)
*PS = parasympathetic(b)
Cranial nerves
I – VI
I
II
III
IV
V
VI
Olfactory
Optic
Oculomotor
Trochlear
Trigeminal
Abducens
Yes (smell)
Yes (vision)
No
No
Yes (general
sensation)
No
No
No
Yes
Yes
Yes
Yes
No
No
Yes
No
No
No
Cranial nerves
VII – XII
Sensory
function
Motor
function
PS*
fibers
Sensory
function
Motor
function
PS*
fibers
VII
VIII
IX
X
XI
XII
Facial
Vestibulocochlear
Glossopharyngeal
Vagus
Accessory
Hypoglossal
Yes (taste)
Yes (hearing
and balance)
Yes (taste)
Yes (taste)
No
No
Yes
Some
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
No
Cranial Nerves
• MANY mnemonics to help you remember
name, order, and function
– Google at your own risk
• A few possibilities…
Table 13.2
Loss of function casues ptosis, external strabismus (“down and out” ) Trochlear Nerve Palsy
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Table 13.2
Testing function Trigeminal neuralgia Loss of function causes internal strabismus
Table 13.2
Vestibulocochlear Nerve Test
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Table 13.2 Table 13.2
Accessory Nerve Testing
Hypoglossal nerve testing
Functions of the cranial nerves
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)
Figure 13.6
Cervical
nerves
C1 – C8
Thoracic
nerves
T1 – T12
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Cervical plexus
Intercostal
nerves
Cervical
enlargement
Lumbar
enlargement
Cauda equina
Brachial plexus
Lumbar plexus
Sacral plexus
Note: only 7
cervical vertebrae
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Coccygeal (1)Snack at 1AM
Spinal Nerve Organization
• 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
– 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– Emerge from vertebral column via the intervertebral
foramina
Figure 12.32Figure 12.32Figure 12.32Figure 12.32
SomaticSomaticSomaticSomaticsensorysensorysensorysensoryneuron neuron neuron neuron
Dorsal root (sensory)Dorsal root (sensory)Dorsal root (sensory)Dorsal root (sensory)
Dorsal root ganglionDorsal root ganglionDorsal root ganglionDorsal root ganglion
VisceralVisceralVisceralVisceralsensory sensory sensory sensory neuronneuronneuronneuron
SomaticSomaticSomaticSomaticmotor neuron motor neuron motor neuron motor neuron
Spinal nerveSpinal nerveSpinal nerveSpinal nerve
Ventral rootVentral rootVentral rootVentral root(motor) (motor) (motor) (motor)
Ventral hornVentral hornVentral hornVentral horn(motor neurons)(motor neurons)(motor neurons)(motor neurons)
Dorsal horn (interneurons)Dorsal horn (interneurons)Dorsal horn (interneurons)Dorsal horn (interneurons)
VisceralVisceralVisceralVisceralmotormotormotormotorneuron neuron neuron neuron
Interneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neuronsInterneurons receiving input from somatic sensory neurons
Interneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neuronsInterneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neuronsVisceral motor (autonomic) neuronsVisceral motor (autonomic) neuronsVisceral motor (autonomic) neurons
Somatic motor neuronsSomatic motor neuronsSomatic motor neuronsSomatic motor neurons
Afferent
Efferent
Spinal Nerve Organization
• Rami
– Each spinal nerve branches into mixed rami
• Dorsal ramus
• Ventral ramus
– Rami communicantes branch off of ventral ramus
– Involved in ANS signaling pathways
• Meningeal branch
– Reenters the vertebral canal and innervates the meninges and
blood vessels within
Figure 13.7 (a)
Dorsal root
ganglion
Gray matter
White matter
Ventral root
Dorsal root
Dorsal and
ventral rootlets
of spinal nerve
Dorsal ramus
of spinal nerve
Ventral ramus
of spinal nerve
Sympathetic trunk
ganglion
Spinal nerve
Rami communicantes
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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Spinal Nerve Organization
• Dorsal ramus
– Innervates
• Deep back muscles
• Posterior surface of trunk (skin and muscle)
• Ventral ramus
– Innervates
• Superficial back muscles
• Limbs
• Lateral and anterior surfaces of trunk (skin and muscle on side, chest, ribs, abdominal wall)
Figure 13.7 (b)
Dorsal ramus
Ventral ramus
Intercostal nerve
Spinal nerve
Rami communicantes
Dorsal root
ganglion Dorsal rootVentral root
Sympathetic trunk
ganglion
Sternum
(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
Branches of intercostal
nerve • Lateral cutaneous• Anterior cutaneous
Distribution of Spinal Nerves
• Dermatome
– Area of skin innervated by the cutaneous branches
of a single spinal nerve
– All spinal nerves except C1 participate in
dermatomes
– Most dermatomes overlap
Figure 13.12
C2
C3
C4
C5
T1
T2
T2T3T4T5
C6
C8C7 C7
C6
T6
T7
T8
T9
T10
T11
T12L1
S2S3
L1
L2
L3
L4
L5
L2
L3
L4
L5
S1
C5
C6
C8
T2
C5
C6
S1
Anterior
view
C2
C3
C4
C5
C6
C7C8
C8 C8
C7 C7
T1
T2
T3
T4T5T6T7T8T9
T10
T11
T12
L1L2
L3
S1
(b) Posterior
view
L5S2
S1
S1
S3
S2 S1S2
S4
S5
L5L5
L4
L5L5
L4
C6 C6
C5
L4
L3
L2
L1
L4
Plexuses
• All ventral rami form interlacing nerve networks
– 4 plexuses
• Cervical, brachial, lumbar, and sacral
– Fibers from the rami branch and become redistributed
– Each nerve exiting the plexus has fibers from several spinal nerves
• Advantage?
• Exception: ventral rami of T2–T12
– Do not form a plexus
– Form intercostal nerves
Figure 13.6
Cervical
nerves
C1 – C8
Thoracic
nerves
T1 – T12
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Cervical plexus
Intercostal
nerves
Cervical
enlargement
Lumbar
enlargement
Cauda equina
Brachial plexus
Lumbar plexus
Sacral plexus
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Plexuses
• Cervical plexus
– Formed by ventral rami of C1–C4
– Innervates skin & muscles of the neck, ear, back of
head, and shoulders
Figure 13.8
Hypoglossal
nerve (XII)
C1
C2
C3
C4
C5
Segmental
branches
Lesser occipital
nerveGreater auricular
nerve
Ansa cervicalis
Phrenic nerve
Supraclavicular
nerves
Accessory nerve (XI)
Transverse
cervical nerve
Ventral
rami:
Ventral rami
Plexuses
• Phrenic nerve
– Major motor and sensory nerve of the diaphragm
• Critical for breathing
– Receives fibers from C3–C5
• Therefore receives innervation from both the cervical
plexus and the brachial plexus
Plexuses
• Brachial plexus
– Formed by ventral rami of C4– T1
– Gives rise to the nerves that innervate the upper limb
• Median
• Ulnar
• Axillary
• Radial
• Musculocutaneous
Figure 13.9 (a)
Upper
Middle Trunks
Lower
Roots (ventral rami):
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneous
nerves of the arm
and forearm
Long thoracic
Medial pectoral
Lateral pectoral
Nerve to
subclaviusSuprascapular
Dorsal scapular
Posterior
divisions
Anterior
divisions
Lateral
PosteriorCords
Medial
Axillary
Musculo-
cutaneous
Radial
Median
Ulnar
Posterior
divisions
Trunks Roots
C4
C5
C6
C7
C8
T1
(a) Roots (rami C5 – T1), trunks, divisions, and cords
Figure 13.9 (c)
Median nerve
Musculocutaneous nerve
Radial nerveHumerus
Ulna
Ulnar nerveMedian nerve
Radius
Radial nerve (superficial branch)
Superficial branch of ulnar nerveDorsal branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Digital branch
(c) The major nerves of the upper limb
Axillary
nerve Anterior
divisions
Posterior
divisions
Trunks Roots
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Injuries
• Radial nerve damage causes the fingers, wrist, or hand to be in
the chronically flexed position
– “Crutch paralysis” – caused when crutches are improperly
adjusted
– “Saturday night paralysis” – caused by falling asleep with the
arm hanging over the armrest of a chair
– “Honeymoon paralysis” – caused by someone else sleeping
on and compressing the arm
Injuries
• Radial nerve damage causes the fingers, wrist,
or hand to be in the chronically flexed position
– Radial nerve is constantly pushed against the
humerus, and cannot innervate extensor muscles
– Improves quickly with therapy
Injuries
• Ulnar nerve is the largest nerve in the body that
is not protected by muscle or bone
• Injury is common
– “Funny bone”
– Weakness in flexion of the hand at wrist, inability to
cross fingers
– “Claw hand” at rest
Injuries• Carpal tunnel
– Caused when the median nerve is compressed as it travels
through the wrist
– Pain, numbness, tingling in the hand, forearm, and shoulder
– Caused by anything that applies pressure to the median
nerve
• Esp. cumulative trauma caused by repetitive motion
– If untreated may cause wasting on muscles at the base of the
thumb
Plexuses
• Lumbar plexus
– Arises from L1–L5 (some T12)
– Innervates thigh, abdominal wall, external genitalia, leg & foot
• Femoral nerve
– Innervates quadriceps, skin of anterior thigh & medial surface of leg
– Functions in extending the knee; sensory function in skin on front and inner sides of thigh, shin, and arch of foot
• Obturator nerve
– Passes through obturator foramen
– Innervates adductor muscles; sensory function in skin on medial aspect of thigh
Figure 13.10
(a) Ventral rami and major branches
of the lumbar plexus
Iliohypogastric
L1
L2
L3
L4
L5
Ilioinguinal
Genitofemoral
Lateral femoral
cutaneous
Obturator
Femoral
Lumbosacral
trunk
Lateral femoral
cutaneous
Anterior femoral
cutaneous
Saphenous
Obturator
Iliohypogastric
Ilioinguinal
Femoral
Ventral ramiVentral
rami:
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
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Plexuses
• Sacral plexus
– Arises from L4–S4
– Serves the buttock, lower limb, pelvic structures & perineum
– Gives rise to sciatic nerve
• Longest and thickest nerve of the body
• Innervates
– Muscles of the leg and foot
– Skin on the leg and foot
Figure 13.11 (a)
Superior
gluteal
Lumbosacral
trunkInferior
gluteal
Common
fibular
Tibial
Posterior
femoral
cutaneousPudendal
Sciatic
Ventral rami and major branches
of the sacral plexus
L4
L5
S1
S2
S3
S4
S5
Co1
Ventral rami Ventral rami:
Figure 13.11 (b)
Superior gluteal
Inferior gluteal
Common fibular
Deep fibular
Superficial fibular
Plantar branches
Tibial
Sural (cut)
Posterior femoral
cutaneous
Pudendal
Sciatic
(b) Distribution of the major nerves from
the sacral plexus to the lower limb