Enclosed by an insulating myelin sheath, made largely of phospholipids (80% lipid and 20% protein), formed by Schwann cells that wrap around whole axon length
Schwann cells spiral around, enclosing axon in their many plasma membrane layers; spaces between cells are Nodes of Ranvier; occur every 1-3mm
Speeds up nerve impulse transmission, since Na+ and K+ ion movement and therefore action potentials, can only occur at the Nodes of Ranvier, they jump from node to node impulse conduction is saltatory conduction
