The ulnar and median nerves share the innervation to the hand and volar compartment of the forearm. The median nerve supplies most of the volar forearm compartment, and the ulnar nerve supplies most of the hand. In the hand, the median nerve supplies the thenar eminence and radial two lumbricals, as well sensation to the palmar surface of the radial 3 and a half fingers and palm, and nailbeds dorsally.
The median nerve (C5-T1) is formed from branches from the medial cord and lateral cord. It descends down the middle of the arm; initially lateral to the brachial artery, the median nerve becomes medial to the brachial artery prior to reaching the elbow. The nerve does not supply any structures in the arm, and passes down into the forearm, superficial to brachialis and deep to the tendon of biceps brachii. It passes between the two heads of pronator teres and enters the forearm. In the forearm it supplies all the muscles of the flexor compartment (pronator teres, pronator quadratus, flexor pollicis longus, flexor carpi radialis, the radial head of flexor digitorum profundus, flexor digitorum superficialis, and palmaris longus) aside from flexor carpi ulnaris and the ulnar head of flexor digitorum profundus.
The nerve runs underneath flexor digitorum superficialis. It emerges at the wrist, between the tendons of palmaris longus and flexor carpi radialis. At this point it gives off the superficial cutaneous nerve of the palm, which runs superficial to the flexor retinaculum and is therefore spared in carpal tunnel syndrome. The median nerve runs within the carpal tunnel, deep to the flexor retinaculum, but superficial to the tendons of the long finger flexors. It gives motor branches to the radial two lumbricals (flex the metacarpophalangeal joints, and extend the interphalangeal joints of the fingers), and the thenar eminence (flexor pollicis brevis, opponens pollicis and abductor pollicis). Adductor pollicis brevis adducts the thumb but is not a part of the thenar eminence; and is innervated by the ulnar nerve.
Branches- anterior interosseus nerve, palmar cutaneous branch, recurrent motor branch.
Muscles supplied- flexor compartment of the forearm, thenar eminence, radial two lumbricals.
Dermatome- Palmar 3 and a half fingers and palm, including nailbeds.
The emergence of the nerve from the brachial plexus looks like the central line of an M.
Injury to the median nerve can result in the "Hand of Benediction". The when the patient is asked to make a fist the patient's index and middle fingers are held in extension due to unopposed action of the extensor tendons. The FDS and FDP as well as the lumbricals are denervated to the second and third fingers .