The Spinal Nerves

山东大学医学院 解剖教研室李振华

31 pairs spinal nerves:

8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerve.

Formation: each spinal nerve is formed by union of anterior and posterior roots at intervertebral foramen The anterior root － contains motor fi

bers for skeletal muscles. Those from T1 to L2 contain sympathetic fibers; S2 to S4 also contain parasympathetic fibers.

The posterior root － contains sensory fibers whose cell bodies are in the spinal ganglion.

General description

Functional components Somatic efferent nerve fibers (SE): fibers that transmit motor impul

ses from spinal cord to skeletal muscles. Visceral efferent nerve fibers (VE): fibers that transmit motor impul

ses from spinal cord to smooth muscles, cardiac muscle and glands. Somatic afferent nerve fibers (SA): fibers that transmit exterocepti

ve and proprioceptive impulses from body to spinal cord Visceral afferent nerve fibers (VA): fibers that transmit interoceptiv

e impulses from the viscera to spinal cord

Branches of spinal nerves Anterior branch: largest , innervates anterolateral body wall and limb

s ， the great nerve plexus, e.g. the cervical, brachial, lumbar, and sacral, are formed by anterior rami

Posterior branch: innervates the back of the trunk Communicating branch: connect the spinal nerve to the sympathetic

trunk Meningeal branch: re-enters vertebral canal through intervertebral for

amen to dura mater

Cervical plexus 颈丛 Formation: formed by anteri

or rami of C1-C4 spinal nerves

Position: lies in front of the origin of levator scapulae and scalenus medius and deep to the superior part of the sternocleidomastoid

Branches Cutaneous branches:

Lesser occipital Great auricular Transverse nerve of neck Supraclavicular nerves

Emerge around middle of posterior border of sternocleidomastoid, to supply skin of neck and scalp between auricle and external occipital protuberance

Muscular branches: supply the deep muscles of neck

Phrenic nerve (anterior rami of C3-C5) to diaphragm (motor and sensory): Descends over scalenus anterio

r to enter thorax Accompanied by pericardiophre

nic vessels and passes anterior to lung roots between mediastinal pleura and pericardium to supply motor and sensory innervation to diaphragm

Sensory fibers supply to pleurae, pericardium and peritoneum of diaphragm; usually right phrenic nerve may be distributed on live, gallbladder and biliary system.

Brachial plexus 臂丛 Formation: Formed by anterior rami

of C5-C8 and T1 spinal nerves

Position: Passes through the scal

ene fissure to posterosuperior of subclavian artery, then enters the axilla to form three cords

Main branche

Musculocutaneous nerve

Distribution: Biceps brachii, brachalis and coracobrachialis ‘BBC nerve’; skin on anterior aspect of forearm

Median nerve

Distribution: Flexor of forearm except brachioradialis, flexor carpi ulnaris and ulnar half of flexor digitorum profundus, thenar except adductor pollicis, first two lumbricals; skin of thenar, central part of palm, palmar aspect of radial three and one-half fingers, including middle and distal fingers on dorsum

Ulnar nerve Distribution: Flexor carp

i ulnaris, ulnar half of flexor digitorum profundus, hypothenar muscles, interossei, 3rd and 4th lumbricals and adductor pollicis; skin of hypothenar, palmar surface of ulnar one and one-half fingers, ulnar half of dorsum of hand, posterior aspect of ulnar two and one-half fingers

Injury: clawhand

Radial Distribution: Extensor m

uscles of arm and forearm, brachioradialis; skin on back of arm, forearm, and radial side of dorsum of hand and radial two and one-half fingers

Axillary 腋神经 Distribution: Deltoi

d and teres minor muscle; skin over deltoid and upper posterior aspect of arm

Injury: result in deltoid andteres minor paralysis (loss of shoulser abdution and weel external rotation) with loss of sensation over the deltoid

Anterior branches of thoracic nerves Intercostal nerves (anterior ra

mi of T1- T11) Subcostal nerve (anterior ram

us of T12) Distribution: distributed to inter

costales and anterolateral abdominal muscles, skin of thoracic and abdominal wall, parietal pleura and peritoneum

T2 Sternal angle T4 Nipple T6 Xiphoid process T8 Costal arch T10 Umbilicus T12 Midpoint between umbilicu

s and symphysis pubis

Lumbar plexus Formation: formed by anter

ior rami of L1-L3, a part of anterior rami of T12and L4

Position: lies within substance of psoas major

Branches Iliohypogastric Ilioinguinal Lateral femoral cutaneous Femoral Obturator Genitofemoral

Femoral Runs downward and laterall

y between psoas and iliacus, passes deep to inguinal ligament; supplies anterior thigh muscles (quadriceps, sartorius and pectineus), hip and knee joint, and skin on anteromedial side of thigh, saphenous nerve is distributed to skin of medial side of leg and foot

Obturator Enters thigh through obturat

or foramen; supplies medial group of muscles of thigh, obturator externus, and skin of medial side of thigh

Sacral plexus 骶丛

Formation: formed by anterior rami of L4 and L5 spinal nerves (the lumbrosacral trunk) and anterior rami of sacral and coccygeal nerves

Position: lies in pelvic cavity, anterior to sacrum and piriformis

Branches Superior gluteal Pudendal Posterior femoral cutaneou Sciatic

Sciatic nerve

Leaves pelvis through infrapiriform foramen to enter gluteal region, runs inferiorly laterally deep to gluteus maximus, passing midway between the greater trochanter of femur and ischial tuberosity to back of thigh, lying deep to long head of biceps femoris, normally divided into tibial and common peroneal nerves just above popliteal fossa; innervates semitendinosus, semimembranosus and biceps femoris and has articular branches to hip and knee joints

Tibial nerve

Decends through popliteal fossa and lies on popliteus; then runs inferiorly with posterior tibial vessels and terminates beneath flexor retinaculum by dividing into medial and lateral plantar nerves; supplies posterior muscles of leg and knee joint

Common peroneal nerve Arises at apex of popliteal fossa and follows media

l border of biceps femoris and its tendon; passes over posterior aspect of head of fibula and then winds around neck of fibula, deep to peroneus longus, where it divides into deep and superficial peroneal nerves

Deep peroneal nerve Arises between peroneus longus and neck of fibula;

descends on interosseous membrane and enters dorsum of foot; supplies anterior muscles of leg, and skin of first interdigital cleft

Superficial peroneal Arises between peroneus longus and neck of fibula

and descends in lateral compartment of leg; supplies peroneus longus and brevis and skin on anterior surface of leg and dorsum of foot

Superficial peroneal

Deep peroneal