The median nerve is one of the four main nerves that supply the upper limb (arm, forearm, and hand). The others are the ulnar, musculocutaneous, and radial; all of them originating from the brachial plexus. The median nerve innervates all the flexor muscles lying in the anterior compartment of forearm: flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, and flexor pollicis brevis muscle.
Origin and Course
It is a mixed nerve which originates by the merging of two side branches, one arising from the lateral, and the other from the medial cord of the brachial plexus. Before joining together into one, the lateral (outer) and medial (inner) branch straddle the last portion of the axillary artery, embracing it.
Nerve fibers from the fifth, sixth, and seventh cervical (C5-C6-C7) join together to make up the median nerve, traveling through the lateral and medial cord. First it runs along the medial side of the arm. Then it extends along the middle of forearm, stretching into the hand. As it runs through the arm, it first lies on the lateral side of the brachial artery. Then it switches over to the other side of this blood vessel to position itself on the medial side of the brachial artery.
Once it has reached the forearm, it gives off the anterior interosseous branch. Then the median nerve runs between the two heads of the pronator teres muscle, crossing the ulnar artery. Next, it extends between the flexor digitorum superficialis and the flexor digitorum profundus. Finally, it runs through the carpal tunnel, supplying the flexor pollicis brevis and the opponens pollicis of thumb and the second and first lumbrical muscles of hand.
Innervation
The median nerve gives off efferent branches to supply all the superficial muscles of forearm, except for the flexor carpi ulnaris, which is supplied by the ulnar nerve. It also supplies the muscles of the thenar (thumb), except for the adductor pollicis. Meanwhile, its afferent (sensory) nerve fibers innervate the skin of forearm.
Below, drawing showing the location in the arm of the median, ulnar, and musculocutaneous nerve.
Schematic drawing of brachial plexus, exhibiting the origin of the median, ulnar, radial, and musculocutaneous nerve.
