Myelin sheath is absent in:-: (A) Pre-axon, (B) Axons of CNS, (C) Optic nerve., (D) Motor roots.
Answer is A. Myelin sheath is absent at following sites:- 1) Nodes of Ranvier 2) Proximal pa of Axon (Pre axon) 3) Near the termination of Axon. 4) At the clefts of Schmidt- Lantermann.