The median nerve is one of the five main nerves originating from the brachial plexus and provides motor and sensory innervation to parts of the forearm and hand.
- lateral root: lateral cord of the brachial plexus (C5, C6, C7)
- medial root: medial cord of the brachial plexus (C8, T1)
- course: laterally to the axillary artery, descends in the arm between biceps brachii and triceps brachii muscles, courses through the forearm with the ulna nerve and vessels before entering the carpal tunnel to the hand
- major branches: anterior interosseous nerve, palmar cutaneous branch, motor branch in the hand
- motor supply: flexor compartment of the forearm, thenar and intrinsic hand muscles
- sensory supply: skin over thenar eminence, palmar aspect of the thumb, index, middle finger and radial half of the ring finger
The median nerve is formed from a lateral root from the lateral cord and a medial root from the medial cord of the brachial plexus. It forms from nerve roots originating at C5-T1.
In the axilla, the median nerve lies lateral to the axillary artery. It enters the arm from axilla at the inferior margin of the teres major muscle and descends medially between biceps brachii and triceps brachii. In the arm, the median nerve courses laterally to the brachial artery and then crosses it, usually anteriorly, from lateral to medial. It lies initially on coracobrachialis, then brachialis.
The median nerve leaves the bicipital aponeurosis and enters the forearm between the two heads of pronator teres muscle and gives off the anterior interosseous nerve. It courses towards the wrist deep to flexor digitorum superficialis and superficial to flexor digitorum profundus muscle. It emerges lateral to the flexor digitorum superficialis about 5 cm proximal to the wrist (giving off the palmar cutaneous branch) and enters the hand through the carpal tunnel (the only nerve to traverse the carpal tunnel), passing deep to the flexor retinaculum at the wrist. On entering the palm, it gives off motor and cutaneous branches.
- muscular branch just above elbow supplies pronator teres muscle (lying within the superficial layer of forearm flexors)
- muscular branch at elbow: supplies remainder of superficial layer of forearm flexors (including flexor carpi radialis and palmaris longus, with the exception of flexor carpi ulnaris) and intermediate layer of forearm flexors (flexor digitorum superficialis)
- anterior interosseous nerve: supplies flexor pollicis longus, pronator quadratus and radial half of flexor digitorum profundus
- palmar cutaneous branch: arising from vololateral aspect before median nerve entering wrist, superficial to the carpal tunnel and lies between palmaris longus and flexor carpi radialis and supplies the cutaneous innervation to the palm and skin over thenar eminence
- recurrent branch: motor branch in the hand: supplies thenar muscles including abductor pollicis brevis, superficial head of flexor pollicis brevis, and opponens pollicis and the radial two lumbricals
- leaves the carpal tunnel over the distal border of the flexor retinaculum onto flexor pollicis brevis to terminate by passing into the thenar eminence
- digital cutaneous branch: palmar aspect and dorsal nail beds of the thumb, index and middle fingers and the radial half of the ring finger
- articular branches to the elbow, wrist, carpal and phalangeal joints
- high division or bifid median nerve
- median nerve (normal or bifid) may be accompanied by a persistent median artery of the forearm
- accessory branches arising proximal or distal to the carpal tunnel
- variant course of thenar branch
- aberrant origin to the motor branch (under the flexor retinaculum or through the flexor retinaculum)
- anastomoses between median and ulnar nerves which may complicate clinical examination or EMG studies:
- Martin-Gruber nerve: between median nerve or anterior interosseous branch and ulnar nerve
- Riche-Cannieu anastomosis: between deep branch ulnar nerve and recurrent branch median nerve
- Berrettini anastomosis: between digital sensory nerve of ulnar and median nerves