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myelin sheath

(Science: anatomy, neurology) An insulating layer surrounding vertebrate peripheral neurons, that dramatically increases the speed of conduction. It is formed by specialised 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. A layer of myelin encasing (and insulating) the axons of medullated nerve fibers.A layer of [[ phosphoplipids that surrounds nerve fibres.