Download The Nervous System Peripheral Nervous System (PNS) Cranial

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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
The Nervous System
Cranial and spinal Nerves
Axon
Endoneurium
Myelin sheath
Perineurium
Epineurium
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent)
division
Fascicle
Motor (efferent) division
Blood
vessels
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
(b)
Figure 13.3b
Figure 13.1
Cranial Nerves
Frontal lobe
• 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
Temporal lobe
Infundibulum
Facial
nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Filaments of
olfactory
nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve
(II)
Optic chiasma
Optic tract
Oculomotor
nerve (III)
Trochlear
nerve (IV)
Trigeminal
nerve (V)
Abducens
nerve (VI)
Cerebellum
Medulla
oblongata
(a)
Figure 13.5 (a)
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Cranial nerves
I – VI
Sensory
function
Motor
function
PS*
fibers
I Olfactory
Yes (smell)
No
No
II Optic
III Oculomotor
Yes (vision)
No
No
Yes
No
Yes
IV Trochlear
V Trigeminal
No
Yes (general
sensation)
Yes
Yes
No
No
Yes
No
VI Abducens
Cranial nerves
VII – XII
VII Facial
VIII Vestibulocochlear
Sensory
function
Motor
function
• MANY mnemonics to help you remember
name, order, and function
– Google at your own risk
• A few possibilities…
PS*
fibers
Yes (taste)
Yes (hearing
and balance)
Yes
Some
Yes
No
IX Glossopharyngeal
Yes (taste)
Yes
Yes
X Vagus
Yes (taste)
Yes
Yes
No
No
Yes
Yes
No
No
XI Accessory
XII Hypoglossal
(b)
No
Cranial Nerves
*PS = parasympathetic
Figure 13.5 (b)
Table 13.2
Loss of function casues ptosis, external strabismus (“down and out” )
Trochlear Nerve Palsy
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Testing function
Trigeminal neuralgia
Loss of function causes internal strabismus
Table 13.2
Vestibulocochlear Nerve Test
Table 13.2
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Accessory Nerve Testing
Table 13.2
Table 13.2
Functions of the cranial nerves
Hypoglossal nerve testing
Spinal Nerves
Cervical plexus
Brachial plexus
• 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)
Cervical
enlargement
Intercostal
nerves
Cervical
nerves
C1 – C8
Note: only 7
cervical vertebrae
Thoracic
nerves
T1 – T12
Lumbar
enlargement
Lumbar plexus
Sacral plexus
Cauda equina
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Figure 13.6
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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
Snack at 1AM
Coccygeal (1)
Spinal Nerve Organization
Afferent
Dorsal root (sensory)
Dorsal root ganglion
Dorsal horn (interneurons)
Somatic
sensory
neuron
• Rami
– Each spinal nerve branches into mixed rami
Visceral
sensory
neuron
• Dorsal ramus
• Ventral ramus
Visceral
motor
neuron
– Rami communicantes branch off of ventral ramus
– Involved in ANS signaling pathways
Spinal nerve
Ventral root
(motor)
Somatic
motor neuron
Ventral horn
(motor neurons)
• Meningeal branch
– Reenters the vertebral canal and innervates the meninges and
blood vessels within
Interneurons receiving input from somatic sensory neurons
Efferent
Interneurons receiving input from visceral sensory neurons
Visceral motor (autonomic) neurons
Somatic motor neurons
Figure 12.32
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.
Figure 13.7 (a)
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Spinal Nerve Organization
Dorsal ramus
Ventral ramus
• Dorsal ramus
Spinal nerve
– Innervates
Rami communicantes
• Deep back muscles
• Posterior surface of trunk (skin and muscle)
Intercostal nerve
Dorsal root
ganglion
Dorsal root
Ventral root
Branches of intercostal
nerve
• Lateral cutaneous
• Anterior cutaneous
Sympathetic trunk
ganglion
• Ventral ramus
– Innervates
• Superficial back muscles
• Limbs
• Lateral and anterior surfaces of trunk (skin and muscle on
side, chest, ribs, abdominal wall)
Sternum
(b) Cross section of thorax showing the main roots and
branches of a spinal nerve.
Figure 13.7 (b)
Distribution of Spinal Nerves
C2
C3
C4
C5
C6
C7
C8
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
C2
C3
C4
• 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
C5
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T2
C5
C6
C6
C7
L1
C8
L2
T12
S2
S3
T2
C5
C6
C8
L2
S1
L4
S3
S4
S5
C6
C7
S2
C6
C7
C8
C8
L2
S2
S2
S1
L1
L3
L5
L4
T11
T12
L1
L3
L5
C7
C6
L1
S1
L3
C5
L2
L5
L4
L3
L5
L5
L4
S1
Anterior
view
S1
(b) Posterior
view
L4
L5
L4
L5
S1
Figure 13.12
Plexuses
Cervical plexus
Brachial plexus
• 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?
Cervical
enlargement
Intercostal
nerves
Thoracic
nerves
T1 – T12
Lumbar
enlargement
Lumbar plexus
• Exception: ventral rami of T2–T12
– Do not form a plexus
– Form intercostal nerves
Cervical
nerves
C1 – C8
Sacral plexus
Cauda equina
Lumbar
nerves
L1 – L5
Sacral nerves
S1 – S5
Coccygeal nerve Co1
Figure 13.6
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Plexuses
Ventral rami
• Cervical plexus
Segmental
branches
– Formed by ventral rami of C1–C4
– Innervates skin & muscles of the neck, ear, back of
head, and shoulders
Ventral
rami:
C1
Hypoglossal
nerve (XII)
Lesser occipital
nerve
Greater auricular
nerve
Transverse
cervical nerve
Ansa cervicalis
C2
C3
C4
Accessory nerve (XI)
C5
Phrenic nerve
Supraclavicular
nerves
Figure 13.8
Plexuses
Plexuses
• Brachial plexus
• 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
Roots (ventral rami):
C4
C5
Dorsal scapular
Nerve to
subclavius
Suprascapular
Cords
C7
Lateral
C8
Posterior
T1
Medial
Axillary
Musculocutaneous
Radial
Median
Ulnar
Axillary
nerve
Anterior
divisions
Posterior
divisions
Trunks
Roots
Upper
Middle
Trunks
Lower
Humerus
Radial nerve
Long thoracic
Medial pectoral
Lateral pectoral
Upper subscapular
Lower subscapular
Thoracodorsal
Medial cutaneous
nerves of the arm
and forearm
(a) Roots (rami C5 – T1), trunks, divisions, and cords
Posterior
divisions
Median
Ulnar
Axillary
Radial
Musculocutaneous
C6
Posterior
divisions
Anterior
divisions
– Formed by ventral rami of C4– T1
– Gives rise to the nerves that innervate the upper limb
Trunks
Roots
Musculocutaneous nerve
Ulna
Radius
Ulnar nerve
Median nerve
Radial nerve (superficial branch)
Dorsal branch of ulnar nerve
Superficial branch of ulnar nerve
Digital branch of ulnar nerve
Muscular branch
Median nerve
Digital branch
(c) The major nerves of the upper limb
Figure 13.9 (a)
Figure 13.9 (c)
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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
• 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
• 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
• 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
Ventral rami
• Lumbar plexus
– Arises from L1–L5 (some T12)
– Innervates thigh, abdominal wall, external genitalia, leg
& foot
Ventral
rami:
Iliohypogastric
L1
Ilioinguinal
Femoral
Iliohypogastric
Ilioinguinal
L2
Genitofemoral
L3
Lateral femoral
cutaneous
Obturator
L4
Femoral
Lumbosacral
trunk
L5
• 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
Lateral femoral
cutaneous
Obturator
Anterior femoral
cutaneous
Saphenous
(a) Ventral rami and major branches
of the lumbar plexus
(b) Distribution of the major nerves from
the lumbar plexus to the lower limb
Figure 13.10
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Plexuses
Ventral rami
Ventral rami:
L4
• Sacral plexus
Superior
gluteal
Lumbosacral
trunk
Inferior
gluteal
– 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
Common
fibular
Tibial
Posterior
femoral
cutaneous
Pudendal
– Muscles of the leg and foot
– Skin on the leg and foot
Sciatic
L5
S1
S2
S3
S4
S5
Co1
Ventral rami and major branches
of the sacral plexus
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
Figure 13.11 (b)
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