CH 11: Myelin Sheath

myelin sheath

A multilayered lipid and protein covering produced by neurolemmocytes (Schwann cells) in the PNS and by oligodendrocytes in the CNS which surrounds the axons of most neurons; this covering electrically insulates the axon and increases the speed of nerve impulse conduction along its length by saltation; in the periphery, the neurolemmocytes aid in the regeneration of an injured axon by forming a regeneration tube which guides and stimulates regrowth of the axon.

myelinated

A term describing a neuron's axon which is insulated by a myelin sheath to permit saltatory conduction of nerve impulses = action potentials; it is accomplished by either oligodendrocytes in the CNS or neurolemmocytes (Schwann cells) in the PNS.

neurofibral node = node of Ranvier

The gaps in the myelin sheath which occur because the insulating neurolemmocytes (Schwann cells) in the PNS and the oligodendrocytes in the CNS do not quite touch each other along the length of the myelinated axon; it is at these uninsulated gaps that the action potential is propagated in saltatory impulse conduction

myelination

The process of forming a myelin sheath by the repeated spiral wrapping of the outer cell membrane of the myelinating cell ( neurolemmocytes (Schwann cells) in the PNS and oligodendrocytes in the CNS) around a portion of a neuron's axon; this covering electrically insulates the axon and increases the speed of nerve impulse conduction along its length by saltation.