Formed by two heads joining in the axilla, one from the lateral cord and one from the medial cord of the plexus
Median nerve — the 'M' shape.
Anatomy · Brain & nerves
Median nerve
Nerve of the carpal tunnel
Peripheral nerves · upper limb
One of the five terminal branches of the brachial plexus, formed from its lateral and medial cords (roots C5–T1). It runs down the middle of the arm and forearm, passes through the carpal tunnel at the wrist, and supplies most of the flexor muscles of the forearm, the muscles at the base of the thumb, and the skin of the palmar side of the thumb, index, middle and half of the ring finger.
How to spot them
- ▸Formed by a two-pronged 'M' or 'Y' where the lateral and medial cords of the plexus join, in front of the axillary artery
- ▸Descends in the arm beside the brachial artery, crossing it from the outer to the inner side, and passes between the two heads of pronator teres in the forearm
- ▸Enters the hand with nine flexor tendons through the carpal tunnel beneath the flexor retinaculum
- ▸Supplies the thenar eminence, the ball of the thumb, and the skin of the palm's lateral three and a half fingers
What to know
Squeezed at the wrist beneath the flexor retinaculum along with nine tendons, it causes numbness and tingling in the thumb, index and middle fingers
Median nerve — carpal tunnel syndrome.
When damaged high in the forearm, asking the patient to make a fist leaves the index and middle fingers pointing — the 'hand of benediction'
Median nerve — the Pope's blessing sign.
Supplies the muscles at the base of the thumb: the abductor pollicis brevis, opponens pollicis and flexor pollicis brevis, along with the first two lumbricals
Median nerve — remembered as LOAF: Lumbricals 1 and 2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.
Runs down the arm beside the brachial artery, crossing it from the outer to the inner side at the elbow
Median nerve — the artery's constant companion.
Gives sensation to the palm side of the thumb, index and middle fingers and half the ring finger
Median nerve — the lateral three and a half digits.
Tapping over the wrist crease to provoke tingling in the fingers is Tinel's sign, and flexing the wrists for a minute is Phalen's test
Median nerve — clinical tests for carpal tunnel syndrome.
Key ideas
- It supplies most of the forearm's flexors, except flexor carpi ulnaris and the ulnar half of flexor digitorum profundus, which belong to the ulnar nerve.
- The carpal tunnel is a fibro-osseous space: the carpal bones form the floor and the flexor retinaculum the roof.
Quick-fire facts
- •Formed by the lateral root (from the lateral cord, C5–C7) and the medial root (from the medial cord, C8–T1)
- •Has no branches in the arm; in the forearm it gives off the anterior interosseous nerve
- •The palmar cutaneous branch leaves before the carpal tunnel, so the skin of the palm's centre is spared in carpal tunnel syndrome
- •Passes through the carpal tunnel with nine tendons: four each of flexor digitorum superficialis and profundus, and one of flexor pollicis longus
- •Carpal tunnel syndrome is the most common entrapment neuropathy
- •Ape hand — a flat thenar eminence with a thumb that cannot oppose — is the classic sign of a severe lesion
- •LOAF is the mnemonic for the four intrinsic hand muscles it supplies: Lumbricals 1 and 2, Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis
- •Supplies the skin over the palmar surface of the lateral three and a half digits and the nail beds on their back
Drill it — 7 cards
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Sources
- TeachMeAnatomy — Median nerve
- OpenStax — 13.4 The Peripheral Nervous System — Anatomy and Physiology 2e