- myelin sheath
An insulating layer surrounding vertebrate peripheral neurons, that dramatically increases the speed of conduction. It is formed by specialized Schwann cells, that can wrap around neurons up to 50 times. The exposed areas are called nodes of Ranvier: they contain very high densities of sodium channels, and action potentials jump from one node to the next, without involving the intermediate axon, a process known as saltatory conduction.
Dictionary of molecular biology. 2004.