The structure of a typical neuron has a Myelin sheath (myelin is produced by the Schwan cell, in the peripheral nervous system), in the axon area, also certain points called along the axon are called nodes of Ranvier, these are, small unmyelinated areas. When action potentials occur in a neuron, only happen in the nodes of Ranvier (unmyelinated areas). This exact mechanism, saltatory conduction, is made possible by the presence of myelinated areas what makes that the action potential propagates faster than it would in a un unmyelinated axon.
Color code: Yellow are the myelinated areas, and the orange dots between them are the nodes of Ranvier