Oligodendrocyte with arrow

Oligodendrocytes are the glial cells which form the myelin sheath around axons of neurons within the central nervous system. In the peripheral nervous system, this function is performed by Schwann cells. Oligodendrocytes have many processes (unecessarily large green arrow), each of which extends to an axon and wraps around it several times, forming the myelin sheath. Each oligodendrocyte myelinates a short span of many different axons. Oligodendrocytes are damaged in demyelinating disease.