saltatory conduction

Saltatory conduction is the clever trick a nerve fiber uses to send its electrical signal much faster: instead of crawling smoothly down the whole length of the fiber, the signal leaps from one small gap to the next, like a stone skipping across water. The fiber here is an axon, the long cable-like tail a neuron uses to carry its message. Most fast axons are wrapped in a fatty insulating sleeve called myelin, much like the plastic coating on an electrical wire. But that sleeve is not one continuous tube; it comes in segments, with tiny bare gaps between them. Those exposed gaps are the nodes of Ranvier, and the word saltatory comes from the Latin for to leap, because the signal effectively jumps from node to node.

Here is why the jumping works. The nerve signal itself is an action potential, a brief spike of electricity that a neuron generates and passes along. To regenerate that spike, the axon needs special pores in its membrane called ion channels, which let charged particles rush in and out. Crucially, these channels are crowded almost entirely at the bare nodes, while the myelin-wrapped stretches have very few. Under each myelin segment the electrical charge slides through quickly and passively, losing a little strength, and then at the next exposed node a fresh burst of channels fires to rebuild the spike at full power. Because the slow, effortful regeneration step happens only at the widely spaced nodes rather than at every point along the fiber, the signal covers ground far faster and using far less energy than it would in a bare, unmyelinated axon.