<prompt> Myelin sheath in the central nervous system is formed bySchwann cellMicrogliaOligodendrocytesProtoplasmic astrocytes  <response>: 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 