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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