The median nerve controls sensations to the palm side of the thumb and fingers (although not the little finger), as well as impulses to some small muscles in the hand that allow the fingers and thumb to move. Carpal tunnel syndrome occurs when the median nerve, which runs from the forearm into the hand, becomes pressed or squeezed at the wrist. The carpal tunnel, a narrow, rigid passageway of ligament and bones at the base of the hand, houses the median nerve and tendons. At times thickening from irritated tendons or other swelling narrows the tunnel and causes the median nerve to be compressed. Carpal tunnel syndrome is characterized by pain, weakness, or numbness in the hand and wrist, often radiating up the arm.