Nerve · Forearm

Anterior interosseous nerve

Nervus interosseus antebrachii anterior

The median nerve's deep motor branch, given off in the upper forearm and running the length of the interosseous membrane between the two bones, sandwiched between flexor pollicis longus and flexor digitorum profundus, before ending on the back of pronator quadratus. It supplies the three muscles that bend the last joints of the thumb and index finger and that turn the palm downwards. Uniquely among the median nerve's branches it reaches no skin at all: everything it does is movement, plus a few twigs to the wrist joints. That single fact is its clinical signature — when it stops working, the pinch between thumb and index fingertip fails while sensation is entirely normal.