Median nerve

Course

• Descends in the arm alongside the brachial artery, crossing from lateral to medial side near the elbow. It gives no major branches in the arm. Gray's Anatomy for Students, p. 880.
• Passes through the cubital fossa.
• Enters the forearm between the two heads of pronator teres.
• Runs between flexor digitorum superficialis and profundus.
• Enters the hand through the carpal tunnel, deep to the flexor retinaculum.

Motor supply

• Flexor carpi ulnaris - ulnar nerve
• Medial half of flexor digitorum profundus to ring and little fingers - ulnar nerve

• Flexor pollicis longus
• Lateral half of flexor digitorum profundus, mainly index finger
• Pronator quadratus

• Abductor pollicis brevis
• Opponens pollicis
• Superficial head of flexor pollicis brevis

Sensory supply

• Palmar surface of the lateral 3½ digits: thumb, index, middle, and lateral half of ring finger.
• Dorsal distal phalanges/nail beds of the same digits.
• Skin of central palm via the palmar cutaneous branch.

Important clinical correlations

• Carpal tunnel syndrome: Compression beneath the flexor retinaculum produces paraesthesia/numbness in the lateral 3½ digits, thenar weakness or wasting, and impaired thumb opposition. The central palm is usually spared because the palmar cutaneous branch runs superficial to the flexor retinaculum.
• Anterior interosseous nerve palsy: Weak flexion of the thumb IP joint and index DIP joint, causing an abnormal “OK sign.”
• High median nerve injury at elbow: Loss of pronation and weak wrist flexion, impaired thumb opposition, thenar wasting, and inability to flex index and middle fingers normally when making a fist.
• Low injury at wrist: Forearm muscles remain intact, but thenar weakness and sensory loss in the digits occur.