The insulating envelope of myelin that surrounds the core of a nerve fiber or axon and facilitates the transmission of neurological impulses. When you look at the peripheral neurological system, the sheath is formed through the cellular membrane associated with Schwann cell and, within the nervous system, from oligodendrocytes. Also referred to as medullary sheath.
An envelope of myelin that surrounds neurological fibres.
a layer of myelin encasing (and insulating) the axons of medullated nerve fibers