Myelin is an insulator sheath for nerve axons. It is composed of phospholipid lamellae, and offers isolation to the axons, ensuring rapid conduction of nerve impulses.
Axons can be either covered by myelin (myelinated) or bare (unmyelinated). Myelin is found in both the CNS and PNS; however, its composition and means of production are different.
Myelin sheaths are not continuous. They contain gaps which are called nodes of Ranvier (seen above)
Myelin in the PNS and CNS
Both in