Most nerve fibres are surrounded by an insulating, fatty sheath called myelin, which is essential for rapid impulse transmission.
The myelin sheath is an extension of the cell in which most of the cytoplasm is extruded and apposed phospholipid bilayers of the plasmalemma are fused to form the lamellae of compacted myelin.
The myelin membranes originate from, and are part of, Schwann cells in the PNS and oligodendrocytes in the CNS.
Myelin sheath
