Carpal tunnel syndrome occurs when the median nerve, which runs from the forearm to the hand, is compressed or pinched at the wrist. The median nerve controls sensations on the palmar side of the thumb and fingers (though not the little finger), as well as impulses to some small muscles in the hand that allow the fingers and thumb to move. The carpal tunnel (a narrow, rigid corridor of ligament and bones at the base of the hand) houses the median nerve and tendons. Sometimes thickening of irritated tendons or other inflammation narrows the tunnel and causes the median nerve to compress. The result may be pain, weakness, or numbness in the hand and wrist, radiating down the arm.