Nodes of Ranvier are regularly spaced gaps in the myelin sheath around a nerve cellfiber or "axon". About one micrometer in length, these gaps expose the membrane of the axon to the surrounding liquid. In "myelinated" axons, electrical excitation occurs only at the nodes of Ranvier, so that signals hop along these fibers rather than propagating smoothly, as they do in axons that lack a myelin sheath. This is known as saltatory conduction.
