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The median nerve is a nerve that runs down the arm and forearm. It is one of the five main nerves originating from the brachial plexus.
The median nerve is formed from parts of the medial and lateral cords, and continues down the arm. It enters the forearm (with the brachial artery) and innervates most of the flexors in the forearm. It does not innervate flexor carpi ulnaris or the medial two digits of flexor digitorum profundus, which are supplied by the ulnar nerve.
The median supplies the muscles in the thenar eminence of the hand by a recurrent thenar branch, and the lateral two lumbrical muscles. The rest of the intrinsic muscles of the hand are supplied by the ulnar nerve.
In terms of sensory information, the median nerve cutaneously innervates the palmar side of the thumb, the index and middle finger, and half the ring finger. It also receives information from the nail bed of these fingers. The proximal part of the palm is supplied by a palmar branch,the palmar cutaneous brach of the median nerve which leaves the nerve proximal to the wrist creases. This palmar cutaneous branch travels in a separate fascial groove adjacent to the flexor carpi radialis.
The median nerve is the only nerve that passes through the carpal tunnel, so it plays a large part in carpal tunnel syndrome.
Details from Gray's anatomy
The Median Nerve extends along the middle of the arm and forearm to the hand.
It arises by two roots, one from the lateral and one from the medial cord of the brachial plexus; these embrace the lower part of the axillary artery, uniting either in front of or lateral to that vessel.
Its fibers are derived from the sixth, seventh, and eighth cervical and first thoracic nerves.
As it descends through the arm, it lies at first lateral to the brachial artery; about the level of the insertion of the Coracobrachialis it crosses the artery, usually in front of, but occasionally behind it, and lies on its medial side at the bend of the elbow, where it is situated behind the lacertus fibrosus (bicipital fascia), and is separated from the elbow-joint by the Brachialis.
In the forearm it passes between the two heads of the Pronator teres and crosses the ulnar artery, but is separated from this vessel by the deep head of the Pronator teres.
It descends beneath the Flexor digitorum sublimis, lying on the Flexor digitorum profundus, to within 5 cm. of the transverse carpal ligament; here it becomes more superficial, and is situated between the tendons of the Flexor digitorum sublimis and Flexor carpi radialis.
In this situation it lies behind, and rather to the radial side of, the tendon of the Palmaris longus, and is covered by the skin and fascia.
It then passes behind the transverse carpal ligament into the palm of the hand.
In its course through the forearm it is accompanied by the median artery, a branch of the volar interroseous artery.
Branches
With the exception of the nerve to the Pronator teres, which sometimes arises above the elbow-joint, the median nerve gives off no branches in the arm. As it passes in front of the elbow, it supplies one or two twigs to the joint.Branches in the forearm
In the forearm its branches are: muscular, volar interosseous, and palmar.- The muscular branches (rami musculares) are derived from the nerve near the elbow and supply all the superficial muscles on the front of the forearm, except the Flexor carpi ulnaris.
- The volar interosseous nerve (n. interosseus * volaris; anterior interosseous nerve) supplies all of the muscles in the anterior compartment of the forearm, except the medial half of the Flexor digitorum profundus and the flexor carpi ulnaris. It accompanies the volar interosseous artery along the anterior aspect of the interosseous membrane, in the interval between the Flexor pollicis longus and Flexor digitorum profundus, supplying the whole of the former and the radial half of the latter, and ending below in the Pronator quadratus and wrist-joint.
- The palmar branch (ramus cutaneus palmaris n. mediani) of the median nerve arises at the lower part of the forearm. It pierces the volar carpal ligament, and divides into a lateral and a medial branch;
- the lateral branch supplies the skin over the ball of the thumb, and communicates with the volar branch of the lateral antibrachial cutaneous nerve;
- the medial branch supplies the skin of the palm and communicates with the palmar cutaneous branch of the ulnar.
Branches in the hand
In the palm of the hand the median nerve is covered by the skin and the palmar aponeurosis, and rests on the tendons of the Flexor muscles. Immediately after emerging from under the transverse carpal ligament the nerve becomes enlarged and flattened and splits into a smaller, lateral, and a larger, medial portion.The lateral portion supplies a short, stout branch to certain of the muscles of the ball of the thumb, viz., the Abductor brevis, the Opponens, and the superficial head of the Flexor brevis, and then divides into three proper volar digital nerves; two of these supply the sides of the thumb, while the third gives a twig to the first Lumbricalis and is distributed to the radial side of the index finger.
The medial portion of the nerve divides into two common volar digital nerves.
- The first of these gives a twig to the second Lumbricalis and runs toward the cleft between the index and middle fingers, where it divides into two proper digital nerves for the adjoining sides of these digits.
- The second runs toward the cleft between the middle and ring fingers, and splits into two proper digital nerves for the adjoining sides of these digits; it communicates with a branch from the ulnar nerve and sometimes sends a twig to the third Lumbricalis.
Each proper digital nerve, opposite the base of the first phalanx, gives off a dorsal branch which joins the dorsal digital nerve from the superficial branch of the radial nerve, and supplies the integument on the dorsal aspect of the last phalanx.
At the end of the digit, the proper digital nerve divides into two branches, one of which supplies the pulp of the finger, the other ramifies around and beneath the nail.
The proper digital nerves, as they run along the fingers, are placed superficial to the corresponding arteries.
External links
"Median nerve"