Pressure or stretching injuries can make fragile nerve fibers break, causing a loss of feeling and improperly working muscles. In a nerve, the fibers are surrounded by insulation. Sometimes the fibers can break while the insulation remains intact. If a nerve is cut, the nerve fibers and insulation are severed and need surgery to be repaired. New nerve fibers can grow, and the nerve can work again, as long as the insulating cover can be saved. With the cover intact, new nerves can grow about once inch each month, taking about a year for feeling to return. You might have a pins-and-needles sensation in the meantime.