Node of Ranvier

Nodes of Ranvier are gaps in the myelin sheath of a nerve cell's axon. They have multiple ion channels, allowing ions to move in or out of the axon at those points.
This means the gaps are not insulated from the spaces which surround them (the intracellular space). When impulses move along an axon, they will seem to "jump" from one node to the next along the axon. This is known as saltatory conduction (Latin "saltare" "to hop or leap").