P N S

C R A N I A L N E R V E S

S P I N A L N E R V E S

The Nervous System

Peripheral Nervous System (PNS)

All neural structures outside the brain

Sensory receptors

Peripheral nerves and associated ganglia

Motor neuron endings

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) division Sensory (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

Most are mixed in function

Only 2 pairs are purely sensory

Each nerve is identified by

Number (I through XII)

Name

“On occasion, our trusty truck acts funny—very good vehicle anyhow”

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 tract Oculomotor

nerve (III)

Trochlear

nerve (IV)

Trigeminal

nerve (V)

Abducens

nerve (VI)

Cerebellum

Medulla

oblongata

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

Table 13.2

Table 13.2

Table 13.2

Table 13.2

Table 13.2

Table 13.2

Activity

Complete Cranial Nerve Chart

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

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

Spinal Nerve Organization

Dorsal and ventral roots unite to form spinal nerves

Emerge from vertebral column via the intervertebral foramina

Spinal Nerve Organization

Rami

Each spinal nerve branches into mixed rami

Dorsal ramus

Ventral ramus

Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region

Meningeal branch

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.

Spinal Nerve Organization

Dorsal ramus

Innervates

Deep back muscles

Posterior surface of trunk

Ventral ramus

Innervates

Superficial back muscles

Limbs

Lateral and anterior surfaces of trunk

Figure 13.7 (b)

Dorsal ramus

Ventral ramus

Intercostal nerve

Spinal nerve

Rami communicantes

Dorsal root

ganglion Dorsal root Ventral 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

T2

T3

T4

T5

C6

C8

C7 C7

C6

T6

T7

T8

T9

T10

T11

T12

L1

S2

S3

L1

L2

L3

L4

L5

L2

L3

L4

L5

S1

C5

C6

C8

T2

C5

C6

S1

Anterior

view

C2

C3

C4

C5

C6

C7

C8

C8 C8

C7 C7

T1

T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2 L3

S1

(b) Posterior

view

L5 S2

S1

S1

S3

S2 S1 S2

S4

S5

L5 L5

L4

L5 L5

L4

C6 C6

C5

L4

L3

L2

L1

L4

Plexuses

All ventral rami form interlacing nerve networks

4 plexuses

Cervical, brachial, lumbar, and sacral

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

Plexuses

Cervical plexus

Formed by ventral rami of C1–C4

Innervates skin & 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

Figure 13.8

Hypoglossal

nerve (XII)

C1

C2

C3

C4

C5

Segmental

branches

Lesser occipital

nerve Greater auricular

nerve

Ansa cervicalis

Phrenic nerve Supraclavicular

nerves

Accessory nerve (XI)

Transverse

cervical nerve

Ventral

rami:

Ventral rami

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

subclavius Suprascapular

Dorsal scapular

Posterior

divisions

Anterior

divisions

Lateral

Posterior Cords

Medial

Axillary

Musculo-

cutaneous

Radial

Median

Ulnar

Posterior

divisions

Trunks Roots

C4

C5

C6

C7

C8

T1

(a) Roots (rami C5 – T

1), trunks, divisions, and cords

Figure 13.9 (c)

Median nerve

Musculocutaneous nerve

Radial nerve

Humerus

Ulna

Ulnar nerve

Median nerve

Radius

Radial nerve (superficial branch)

Superficial branch of ulnar nerve Dorsal 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

Injuries

Radial Nerve

Ulnar Nerve

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

Obturator nerve

Passes through obturator foramen

Innervates adductor muscles

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 rami Ventral

rami:

(b) Distribution of the major nerves from

the lumbar plexus to the lower limb

Plexuses

Sacral plexus Arises from L4–S4

Serves the buttock, lower limb, pelvic structures & perineum

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

trunk

Inferior

gluteal

Common

fibular Tibial

Posterior

femoral

cutaneous

Pudendal

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