In sharp contrast to the oligodendrocyte, the Schwann cell responds vigorously to most forms of injury (see Chap. 39). An active phase of mitosis occurs following traumatic insult, and the cells are capable of local migration. Studies on their behavior after primary demyelination have shown that they are able to phagocytose damaged myelin. They possess remarkable reparatory properties and begin to lay down new myelin approximately 1 week after a fiber loses its myelin sheath. Studies on PNS and CNS remyelination [40] have shown that by 3 months after primary demyelination, PNS fibers are well remyelinated, whereas similarly affected areas in the CNS show relatively little proliferation of new myelin (see Chap. 29). Under circumstances of severe injury, such as transection, axons degenerate and the Schwann cells form tubes, termed Büngner bands, containing cell bodies and processes surrounded by a single basal lamina. These structures provide channels along which regenerating axons might later grow. The presence and integrity of the Schwann cell basal lamina is essential for reinnervation.