When pressure starts to build up on the median nerve, the blood supply to the outer covering of the nerve slows down and may even be cut off. The medical term for this is ischemia. At first, only the outside covering of the nerve is affected. But if the pressure keeps building up, the inside of the nerve will start to become thickened. New cells, called fibroblasts, form within the nerve and start forming scar tissue. This is thought to produce the feelings of pain and numbness in the hand. If pressure is taken off right away, the symptoms will go away quickly. Pressure that isn't eased right away can slow or even stop the chances for recovery.