Median nerve

Origin and nerve roots

The median nerve arises in the axillary region and it is formed by the unification of the medial and lateral cords of the brachial plexus. It contains fibres from roots of spinal nerves C6-T1, but in some individuals it can also contain fibers from C5.

Course

After its formation from the brachial plexus, the median nerve descends down the centre of the arm in a superficial course. Initially it is lateral to the brachial artery but as it descends, it eventually becomes medial. 

Just before it enters the forearm, the median nerve passes between the tendons of biceps brachii and brachialis. At this point it again becomes lateral to the brachial artery. Next, in order to gain access to the forearm, it passes between the deep and superficial heads of the pronator teres muscle. Once it passes this point, it dives deeper and runs between the flexor digitorum profundus and flexor digitorum superficialis.

The median nerve then passes through the carpal tunnel beneath the flexor retinaculum, and terminates by dividing into two terminal branches, the common palmar digital nerves.

Branches and innervation

The median nerve gives off numerous branches in the forearm and hand regions. The branches in the forearm region include: 

• The muscular branches to pronator teres, palmaris longus, flexor digitorum superficialis and flexor carpi radialis; these branches innervate the corresponding muscles. 
• The anterior interosseus nerve,which supplies the flexor pollicis longus and radial part of flexor digitorum profundus. This branch runs on the interosseous membrane with the anterior interosseous artery,  and passes deep to the pronator quadratus to supply it. It terminates by giving articular branches to the distal radioulnar, radiocarpal and carpal joints. 

The major branches in the hand include:

• The cutaneous nerve of the palm, which supplies the proximal aspect of the palm. This branch does not enter the carpal tunnel and is hence spared in carpal tunnel syndrome.
• The two common palmar digital nerves, the first of which supplies the radial two lumbricals. The second runs between the ring and middle finger, and divides to give the proper digital nerves that provide sensation to certain areas of the hand. 
• The recurrent branch to the muscles of the thenar eminence (flexor pollicis brevis, abductor pollicis brevis, opponens pollicis). It is also known as the ‘million dollar nerve’ to signify its importance for basic hand function. 

Test your knowledge on the arteries, veins and nerves of the elbow and forearm with this integrated quiz.

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To summarize, the median nerve provides the motor supply to the flexor muscles in the forearm, except flexor carpi ulnaris and the ulnar head of flexor digitorum profundus (which is supplied by the ulnar nerve). It also supplies the thenar muscles as well as the radial two lumbricals.

The sensory supply of the median nerve includes:

• The skin of the palmar and distal dorsal aspects of the lateral three-and-the-half digits and adjacent palm.
• The skin of the palmar and distal dorsal aspects of the thumb and radial half of 2nd digit.
• The skin of palmar and distal dorsal aspects of the adjacent sides of 2nd–4th digits.
• The skin of the central palm.

Learn more about the median nerve with our video tutorial and quiz: