Carpal tunnel syndrome involves the median nerve, one of the major nerve supplies to the lower arm and hand. The “tunnel” involved in carpal tunnel syndrome is formed at the wrist by the bones of the hand as the bottom and sides of the tunnel, with a thick, fibrous band of tissue called a ligament forming the top. The median nerve and nine of the tendons connecting the bones of the forearm to the bones of the hand run through this tunnel. Thick membranes that at times may swell cover the tendons. If they swell too much, the median nerve may be pressed up against the ligament forming the top of the tunnel, causing pain.