Sensory innervation

The median nerve provides sensory innervation to the skin of the palmar side of the thumb, index, and middle fingers and the radial half of the ring finger. The radial side of the palm is innervated by the palmar cutaneous branch of the median nerve. This nerve branches from the median nerve proximal to the wrist.

Motor innervation

The nerve innervates most of the flexor muscles of the forearm with the exception of the flexor carpi ulnaris and the medial two digits of the flexor digitorum profundus, which are supplied by the ulnar nerve

Unbranched, the median nerve supplies the following muscles:

  • Pronator teres
  • Flexor carpi radialis
  • Palmaris longus
  • Flexor digitorum superficialis

The anterior interosseus branch supplies the following muscles:

  • Lateral (radial) half of the flexor digitorum profundus
  • Flexor pollicis longus
  • Pronator quadratus

In the hand, the median nerve provides innervation to:

  • 1st and 2nd lumbricals
  • Thenar muscles: abductor pollicis brevis, flexor pollicis brevis, opponens pollicis

Contributing spinal nerve roots

C5, C6, C7, C8, T1

Nerve Course

The median nerve (C5-T1) forms from the medial and lateral cords of the brachial plexus on the ventral aspect of the axillary artery in the axilla and beneath the pectoralis minor’s attachment to the corocoid process. It accompanies the artery through the arm within the axillary sheath in the medial intermuscular septum, deep to the short head of the biceps and lateral to the brachial artery into the cubital fossa. 

  • The median nerve is adjacent to the artery throughout and crosses the artery from lateral to medial at about midbrachium.
  • The presence of an anomalous muscle associated with the latissimus dorsi and pectoralis major, Langer’s muscle, may entrap the median nerve near its origin.
  • The nerve’s superficial course through most of the arm makes it somewhat vulnerable to superficial lacerations but well protected from injury that might accompany a fracture of the humerus.

The nerve enters the forearm by passing through the cubital fossa, deep to the bicipital aponeurosis, medial to the antecubital vein and brachial artery, and separated from the joint capsule by the brachialis muscle.  It is the most medial structure encountered with the exception of the common origin of the flexor and pronator tendons. 

  • The median nerve does not provide motor or sensory innevation until it reaches the elbow, where motor branches most commonly are found at the level of the elbow flexion crease, however, braches have been seen as far as 4 cm proximal to the elbow.
  • The three chief contents of the cubital fossa are the biceps brachii tendon, the brachial artery, and the median nerve
  • The sharp proximal edge of this aponeurosis is a potential entrapment point of the median nerve.

The median nerve leaves the cubital fossa by passing between the two heads of origin of the pronator teres. Just distal to the pronator teres, the nerve passes deep to the proximal border of the flexor digitorum superficialis muscle crossing anterior to the ulnar artery.

  • This border, the sublimis bridge, is fibrous and sharp and is considered another point of entrapment of the median nerve.
  • The motor branches of the median nerve arise from its medial side with the exception of the twig to the deep head of the pronator teres.

The anterior interosseous nerve branches from the median nerve approximately 5 cm distal to the medial epicondyle, which is distal to the sublimis bridge, and courses with the anterior interosseous artery (from the common interosseous artery) disappearing between the flexor pollicis longus and flexor digitorum profundus muscles to lie on the interosseous membrane.

  • The anterior interosseous nerve supplies the flexor pollicis longus, the pronator quadratus, and the lateral half of flexor digitorum profundus
  • The median nerve supplies the pronator teres, the flexor carpi radialis, the palmaris longus, and the flexor digitorum superficialis
  • This branch has been reported entrapped by an accessory head of origin (Gantzer’s muscle) of the flexor pollicis longus muscle.

Distal to the anterior interosseous branch, the median nerve descends posterior to the flexor digitorum superficialis muscle, supplying the muscle as it clings to its posterior surface and appearing distally at its lateral border. Proximal to the wrist, the nerve is deeply located between the tendons of the palmaris longus medially and the flexor carpi radialis muscle laterally.  The median nerve enters the hand by passing through the carpal tunnel as the most ventral structure (posterior to the flexor retinaculum), where it perhaps is the most commonly entrapped nerve in the body.  At the distal end of the tunnel it separates into its terminal branches: the recurrent or muscular branch and multiple digital branches.  The muscular branch passes laterally into the thenar compartment; although it may pass through some portion of the deep flexor retinaculum, it definitely passes through the thenar septum.

  • The median nerve is vulnerable to entrapment as it passes through either of these fibrous layers.
  • Because of its superficial position in the thenar compartment, it is vulnerable to laceration.
  • The median nerve supplies three thenar (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis) and two lumbrical muscles (1 and 2)
  • Its specific location is the halfway point along a line connecting the pisiform and the base of the first MP joint, or within a circle whose center is 2.5 to 4 cm inferior to the tubercle of the scaphoid.

The digital branches are of two types.  A common digital nerve innervates the adjacent sides of two fingers.  This nerve passes toward a web space where it divides into two proper digital nerves.

  • Each proper digital nerve supplies the skin of one-half of the ventral (or dorsal) aspect of a digit.
  • The digital branches of the median nerve are usually three proper branches to the thumb and radial side of the index finger, and two common branches to the web spaces between the index and middle fingers and the middle and ring fingers
  • The proper digital nerve to the index finger and the common digital nerve to the index and middle fingers provide small branches to the first and second lumbrical muscle, respectively.
  • The proper digital nerves have branches that pass dorsally in the distal aspects of the digit so they supply the skin of the entire digit distal to the DIP joint.

The skin of the hand supplied by the median nerve includes the palmar aspects of the thumb, index, and middle fingers and the lateral half of the ring finger; the distal dorsal aspects of the index and middle fingers and half the ring finger; and the corresponding part of the palm. The skin of the central palm is supplied by the palmar branch of the median, which arises proximal to the wrist and passes superficial to the carpal tunnel.

Clinical correlates

Link to clinical conditions

References

Key references