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myelin Diagram of a neuron showing the cell body with nucleus, branching dendrites, a long axon covered by myelin sheaths from Schwann cells, and nodes of Ranvier. Labels identify the nerve impulse path, axon terminals, and synapses, with an inset highlighting the myelin sheath and node structure.
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myelin
myelin Transmission electron micrograph of a myelinated axon.

myelin

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Diagram of a neuron showing the cell body with nucleus, branching dendrites, a long axon covered by myelin sheaths from Schwann cells, and nodes of Ranvier. Labels identify the nerve impulse path, axon terminals, and synapses, with an inset highlighting the myelin sheath and node structure.
myelin sheathThe insulating myelin sheath that covers the axons of many neurons is produced by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system.

myelin, white, insulating sheath on the axon of many neurons. Composed of fatty materials, protein, and water, the myelin sheath is deposited in layers around axons by Schwann cells in the peripheral nervous system and by a type of neuroglia called an oligodendrocyte in the central nervous system. The sheath is interrupted at intervals by gaps called nodes of Ranvier; this structure speeds nerve conduction, as impulses jump from node to node in a process known as saltatory conduction.

This article was most recently revised and updated by Amy Tikkanen.