Nerve · Upper arm

Median nerve

Nervus medianus

The median nerve is the nerve of precision grip. It drives most of the muscles that bend the wrist and fingers and that draw the thumb across the palm, and it carries feeling from the palm side of the thumb, index, middle and half the ring finger. Its famous trouble spot is the carpal tunnel at the wrist, where it shares a tight, unyielding canal with nine tendons and gets squeezed when that space narrows — the classic story being numbness and tingling in exactly those fingers that wakes you at night and eases when you shake the hand out. But the wrist is only the best-known place it can be caught: where along its path the nerve is compressed changes the pattern of numbness and weakness in ways that point precisely to the spot.