Ranvier Rings

Regions of the axon of about 1 micrometer in size which interrupt the myelin sheath at a distance of 0,2 to 2 millimeters. This is where the depolarization of the axon takes place, which jumps from one Ranvier ring to the next and thus transmits the impulse from the nerve cell.

https://de.wikipedia.org/wiki/Ranvier-Schnürring _{(Wikipedia CC-by-sa-3.0)}