Myelin sheath in the central nervous system is formed by
Oligodendrocytes are responsible for myelination in the CNS. In the PNS, Schwann cells form the myelin sheath. The process of myelination begins before bih and is not complete until a year or more after bih. (Ref: Vishram Singh textbook of neuroanatomy, second edition, pg- 19)
Schwann cell
Microglia
Oligodendrocytes
Protoplasmic astrocytes
Brain 