The Spinal Nerves

SHANDONG UNIVERSITY

Liu Zhiyu

General description 31 pairs spinal nerves:

Cervical nerves—8 pairs (C1-C8) Thoracic nerves—12 pairs (T1-T12) Lumbar nerves—5 pairs (L1-L5) Sacral nerves—5 pairs (S1-S5) Coccygeal nerves—1 pair (Co1)

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

otor fibers 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 of Spinal Nerves Somatic efferent nerve fibers (SE): fibers that transmit motor impulses fro

m spinal cord to skeletal muscles. Visceral efferent nerve fibers (VE): fibers that transmit motor impulses fro

m spinal cord to smooth muscles, cardiac muscle and glands. Somatic afferent nerve fibers (SA): fibers that transmit exteroceptive and p

roprioceptive impulses from body to spinal cord Visceral afferent nerve fibers (VA): fibers that transmit interoceptive impuls

es from the viscera to spinal cord

Branches of spinal nerves

Anterior branch Posterior branch Communicating branch Meningeal branch

Cervical plexus

Formation: formed by anterior 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

C1

C2

C3

C4

Branches of Cervical Plexus

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

Branches of Cervical Plexus

Phrenic nerve Arises from anterior rami of C3-C5 (mo

tor and sensory) Runs vertically downward across the fr

ont of the scalenus anterior Enters the thorax by passing betweem

the subclavian a. and v.

Branches of Cervical Plexus

Phrenic nerve Accompanied by pericardiophrenic ves

sels 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 Formation:

Formed by anterior rami of C5-C8 and T1 spinal nerves

Position:

Passes through the scalene fissure to posterosuperior of subclavian artery, then enters the axilla to form three cords

Main branche of brachial plexus

Lateral cord musculocutaneous n. lateral root of median n.

Medial cord medial root of median n. ulnar n.

Posterior cord radial n. axillary n.

Main Branche of Brachial Plexus Musculocutaneous nerve Origin: arises from the lateral cord of th

e brachial plexus.

Distribution: Biceps brachii Brachalis BBC nerve Coracobrachialis Skin on anterior aspect of forearm

Main Branche of Brachial Plexus

Median nerve Origin: arises from the medial and lateral

cord of the brachial plexus. Muscular branches:

Flexor of forearm except brachioradialis flexor carpi ulnaris and ulnar half of flexor digitorum profundus

Thenar except adductor pollicis, first two lumbricals

Cutaneous branches ： Skin of thenar, central part of palm, Palmar aspect of radial three and one-

half fingers, including middle and distal fingers on dorsum

Injury: Apehand

Main Branche of Brachial Plexus

Ulnar nerve Origin: arises from the medial cord of

the brachial plexus. Muscular branches: Flexor carpi ulnaris, ulnar half of flexo

r digitorum profundus, hypothenar muscles, interossei, 3rd and 4th lumbricals and adductor pollicis;

Cutaneous branches ： 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 nerve Origin: arise from the posterior cor

d of the brachial plexus Course: Winds around the back of t

he arm in the spinal groove of the back of the humerus between the heads of the triceps. It pierces the lateral fascial septum above the elbow and divides into superficial and deep branches.

Radial nerve

Distribution: Extensor muscles of arm and f

orearm, brachioradialis; skin on back of arm, forearm, a

nd radial side of dorsum of hand and radial two and one-half fingers

Injury: wristdrop

Main Branche of Brachial Plexus

Axillary Origin: arises from the posterior

cord of the brachial plexus. Distribution: Deltoid 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 rami of T1- T11)

Subcostal nerve (anterior ramus of T12)

Distribution: distributed to intercostales and anterolateral abdominal muscles, skin of thoracic and abdominal wall, parietal pleura and peritoneum

Segmental Innervation of Skin

Adjacent dermatomes overlap considerably, so that to produce a region of complete anesthesia at least three contiguous spinal nerves have to be sectioned.

Segmental Innervation of Skin

Dermatome: the area of skin supplied by a single nerve, and, therefore, a single segment of the spinal cord. On the trunk the dermatomes extend round the body from the posterior to the anterior median plane.

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

mphysis pubis

Lumbar plexus

Formation: formed by anterior rami of L1-L3, a part of anterior rami of T12and L4 L1

L2

L3

L4

Main branche of lumbar plexus

Position: lies within substance of psoas major

Branches Iliohypogastric Ilioinguinal Lateral femoral cutaneous Femoral Obturator Genitofemoral

Branches of Lumbar Plexus

Femoral nerve

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 nerve

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

Sacral Plexus

Formation: formed by anterior rami of L4 and L5 spinal nerves (the lumbrosacral trunk) and anterior rami of sacral and coccygeal nervesPosition: lies in pelvic cavit

y, anterior to sacrum and piriformis

L5

L4

S1

S2

S3

S4S5

Co

Main branches of sacral plexus

Superior gluteal n. Inferior gluteal n. Pudendal n. Posterior femoral cutaneou n. Sciatic n.

Branches of Sacral Plexus 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

Branches of Sacral Plexus

Tibial nerve Decends through popliteal foss

a 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

Branches of Sacral Plexus

Common peroneal nerve

Arises at apex of popliteal fossa and follows medial 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

Branches of Sacral Plexus 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 nerve Arises between peroneus longus and nec

k 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