The Spinal Nerves

1. The Spinal Nerves 山东大学医学院 解剖教研室 李振华

2. General description • 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 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.

3. Functional components • Somatic efferent nerve fibers (SE): fibers that transmit motor impulses from spinal cord to skeletal muscles. • Visceral efferent nerve fibers (VE): fibers that transmit motor impulses from spinal cord to smooth muscles, cardiac muscle and glands. • Somatic afferent nerve fibers (SA): fibers that transmit exteroceptive and proprioceptive impulses from body to spinal cord • Visceral afferent nerve fibers (VA): fibers that transmit interoceptive impulses from the viscera to spinal cord

4. Branches of spinal nerves • Anterior branch: largest , innervates anterolateral body wall and limbs，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 foramen to dura mater

5. Cervical plexus 颈丛 • 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

6. 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

7. Muscular branches: supply the deep muscles of neck • Phrenic nerve (anterior rami of C3-C5) to diaphragm (motor and sensory): • Descends over scalenus anterior to enter thorax • Accompanied by pericardiophrenic 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.

8. Brachial plexus 臂丛 • 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

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

10. Mediannerve 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

11. Ulnar nerve • Distribution: Flexor carpi 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

12. Radial Distribution: Extensor muscles 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

13. Axillary 腋神经 • 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

14. 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 • T2 Sternal angle • T4 Nipple • T6 Xiphoid process • T8 Costal arch • T10 Umbilicus • T12 Midpoint between umbilicus and symphysis pubis

15. Lumbar plexus • Formation: formed by anterior 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

16. Femoral Runs downward and laterally 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 obturator foramen; supplies medial group of muscles of thigh, obturator externus, and skin of medial side of thigh

17. 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

18. Branches • Superior gluteal • Pudendal • Posterior femoral cutaneou • Sciatic

19. 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

20. 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

21. 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 • 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

22. Superficial peroneal Deep peroneal