Nerves - Median

Question 1

What nerve roots make up the median nerve?

Answer 1

C6-T1 (some C5 in some individuals).

Question 2

Motor functions of the median nerve?

Answer 2

1) Flexor and pronator muscles in the anterior compartment of the forearm (except the flexor carpi ulnaris and part of the flexor digitorum profundus, innervated by the ulnar nerve).
2) Thenar muscles
3) Lateral two lumbricals in the hand

Question 3

Sensory functions?

Answer 3

Gives rise to the palmar cutaneous branch, which innervates the lateral aspect of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand.

Question 4

Anatomical course?

Answer 4

The median nerve is derived from the median and lateral cords of the brachial plexus. It contains fibres from roots of C6-T1 (sometimes C5).

After originating from the brachial plexus in the axilla, the median nerve descends down the arm, initially lateral to the brachial artery. Halfway down the arm, the nerve crosses over the brachial artery, and becomes situated medially. The median nerve enters the anterior compartment of the forearm via the cubital fossa.

In the forearm, the nerve travels between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives off two major branches in the forearm:

• anterior interosseous nerve - supplies the deep muscles in the anterior forearm.
• palmar cutaneous nerve - innervates the skin of the lateral palm.

After giving of these nerves, the median nerve enters the hand via the carpal tunnel, which it terminates by dividing into two branches:

• recurrent branch - innervates the thenar muscles
• palmar digital branch - innervates the palmar surface and fingertips of the lateral three and a half digits. Also innervates the lateral two lumbrical muscles.

Question 5

Clinical relevance: Carpal tunnel syndrome

Answer 5

Compression of the median nerve within the carpal tunnel can cause carpal tunnel syndrome.

It is the most common mononeuropathy and is caused by an increased tissue pressure within the carpal tunnel. Whilst risk factors for CTS have been identified (such as diabetes, pregnancy and acromegaly), the exact underlying aetiology is not well understood.

Clinical features include numbness, tingling, and pain in the distibution of the median nerve. Importantly, the palm is usually spared - as the palmar cutaneous branch does not travel through the carpal tunnel. Symptoms can wake the patient from sleep and are usually worse in the morning. If left untreated, chronic CTS can cause weakness and atrophy of the thenar muscles.

Tests for carpal tunnel syndrome can be performed during physical examination:

• Tinel’s sign - tapping the nerve in the carpal tunnel to elicit pain in median nerve distribution.
• Phalen’s manoeuvre - holding the wrist in flexion for 60 seconds to elicit numbness/pain in median nerve distribution.

Treatment involves the use of a splint, holding the wrist in extension overnight to relieve symptoms. If this is unsuccessful. corticosteroid injections into the carpal tunnel can be trialled. Surgical decompression of the carpal tunnel may be required in severe cases.