Human hand with course and branches of the median nerve (yellow). The median nerve is a motor and sensory nerve. Its motor part in the hand mainly innervates the muscles of the thumb. Clearly visible is the sensory innervation of the first three fingers and the medial part of the forth finger (ring finger). At the wrist joint it runs under a ligament, the transverse carpal ligament. If it gets mechanically compressed or even jammed by this ligament, it leads to the carpal tunnel syndrome. This leads to pain, paraesthesias, sensation of cold or muscular weakness in the area of the nerve.