A neuron has three basic parts: the dendrites, the cell body, and the axons. Some neurons have a fatty layer covering called Schwann sheath around their axons. This layer isn’t continuous, and the gaps are called nodes of Ranvier. The action potential jumps through these gaps to increase the speed of the transmission.
EXPLANATION:
Schwann cells are a variety of glial cells that primarily provide myelin isolation from the axons of the vertebrate peripheral nervous system. It exists only at the peripheral nervous system, whereas oligodendrocytes play this role in the central nervous system, they constitute the myelin sheath around a single axon
The gap between two Schwann cells (the area not covered by the myelin sheath) is called Ranvier's Nodes. These nodes are important ion exchange sites between the axon and extracellular fluids (found in particular in the somatic nervous system).
This arrangement allows saltatory conduction of the high-speed action potential (PA "jumps" over myelin which gives a speed sometimes greater than one hundred meters per second), as well as energy savings.
