Median nerve: anatomy, location and function

The median nerve (Nervus medianus) is a nerve of the upper limb that carries signals for muscle movement and skin sensation. It arises from the brachial plexus, a network of nerves supplying the upper limb, and runs through the arm and forearm before entering the hand through the carpal tunnel, a passage at the wrist.

Where does the median nerve come from?

The median nerve belongs to the peripheral nervous system, the nerves and associated structures outside the brain and spinal cord. It is a mixed nerve: motor fibres carry signals to muscles, while sensory fibres carry information from tissues towards the spinal cord.

It forms from a lateral root and a medial root of the brachial plexus. These roots arise from the lateral and medial cords, bundles of nerve fibres named for their positions around the axillary artery in the armpit. The roots unite near this artery, and the nerve carries fibres derived from spinal nerve levels C6–T1, with a variable contribution from C5.

For description, its course can be divided into regions in the arm, forearm, wrist and hand. These are continuous portions of the same nerve, not separate nerves.

Where is the median nerve in the arm and elbow?

In the upper arm, the median nerve initially lies lateral to the brachial artery, meaning towards the outer side of the limb. It usually crosses in front of the artery and lies medial to it, towards the inner side, near the elbow. It normally gives no muscular branches in the arm.

At the elbow, it passes through the cubital fossa, the triangular hollow on the front of the joint. Here it lies medial to the brachial artery and deep to the bicipital aponeurosis, a broad sheet of tendon extending from the biceps brachii muscle into the connective tissue of the forearm.

The nerve then usually passes between the two heads of the pronator teres muscle. These heads are separate attachment portions of a muscle that turns the forearm so the palm faces backwards in the anatomical position.

How does the median nerve pass through the forearm and wrist?

After passing the pronator teres muscle, the nerve runs beneath a fibrous arch of the flexor digitorum superficialis muscle. It descends between this muscle and the deeper flexor digitorum profundus muscle. Both muscles bend the fingers, but act on different finger joints.

Near the wrist, the nerve becomes more superficial and lies medial to the flexor carpi radialis tendon and deep to the palmaris longus tendon when the latter is present. Tendons are the strong connective-tissue structures that transmit muscle force to an attachment.

The nerve enters the hand through the carpal tunnel alongside the long finger- and thumb-flexor tendons. The wrist bones form the floor and sides of this passage, while the flexor retinaculum, a strong connective-tissue band, forms its roof. The median nerve lies deep to this band.

What are the main branches of the median nerve?

The nerve gives muscular branches in the forearm and branches for movement and sensation in the hand. Important named branches follow different routes, so not every branch entering the hand passes through the carpal tunnel.

The radius and ulna are the forearm bones; the interosseous membrane is the connective-tissue sheet between them. “Cutaneous” means supplying skin, and “digital” refers to the fingers.

Which muscles does the median nerve supply?

Through its connections with the muscular system, the median nerve supports forearm rotation, wrist and finger bending, and precise thumb movements. In the forearm, it supplies most muscles of the anterior compartment, the muscle group on the front of the forearm.

Its main muscular distribution includes:

• Pronator teres and pronator quadratus, which turn the forearm into pronation, with the palm facing backwards from the anatomical position.
• Flexor carpi radialis and palmaris longus, which help bend the wrist.
• Flexor digitorum superficialis, which bends the middle finger joints.
• Flexor pollicis longus and the lateral portion of flexor digitorum profundus, which bend the thumb tip and the tips of the index and middle fingers.
• Abductor pollicis brevis, opponens pollicis and usually the superficial head of flexor pollicis brevis, which position and move the thumb.
• The lateral two lumbrical muscles, small hand muscles that help bend the knuckles while straightening the finger joints.

The anterior interosseous nerve supplies pronator quadratus, flexor pollicis longus and the lateral portion of flexor digitorum profundus. The main forearm exceptions are flexor carpi ulnaris and the medial portion of flexor digitorum profundus, which receive ulnar nerve supply.

Which skin regions receive median nerve sensation?

The median nerve supplies the palmar surfaces of the thumb, index finger, middle finger and the adjacent half of the ring finger. Its digital branches also supply the dorsal, or back, surfaces of their distal ends, including the nail-bed regions.

The palmar cutaneous branch supplies skin over the thumb-side palm, including the thenar eminence, the muscular mound at the base of the thumb. Its route superficial to the flexor retinaculum distinguishes it from the main median nerve, which travels through the carpal tunnel before giving rise to its palmar digital branches in the hand.

How can you follow the median nerve in the 3D model?

In the 3D model next to this article, select the left median nerve or right median nerve, then rotate and zoom to follow its course. Fade or hide neighbouring structures to examine its changing position from the upper arm to the wrist.

Follow the nerve region by region rather than treating it as a straight line. Its relationship to the brachial artery in the arm, the forearm muscles and the flexor retinaculum at the wrist provides a useful sequence of anatomical landmarks.