What is "node of ranvier"

n. (context anatomy English) A small constriction in the myelin sheath of axons

Nodes of Ranvier, also known as myelin sheath gaps, are periodic gaps in the insulating myelin sheaths of myelinated axons where the axonal membrane is exposed to the extracellular space. Nodes of Ranvier are uninsulated and highly enriched in ion channels, allowing them to participate in the exchange of ions required to regenerate the action potential. Nerve conduction in myelinated axons is referred to as saltatory conduction (from the Latin saltare, to hop or leap) because of the manner in which the action potential seems to "jump" from one node to the next along the length of the axon.