Through electrochemical processes, impulse conduction through neurons takes place. This is a type of electrical impulse that travels through the membrane of the axon of a neuron toward the dendrite of another neuron. The membrane is the outer layer of an axon. The impulse that emerges across this membrane is called an action potential. An action potential is created by the rapid influx of positively charged sodium ions at a particular spot in the axon membrane. This causes that spot of the membrane to become positively charged. This is followed by a rapid outflow of positively charged potassium ions, which causes the membrane to become neutral in charge again. The locally generated action potential causes small circuit currents in adjacent membrane sections. This allows the action potential to propagate along the entire length of the axon, towards the dendrite of the next neuron. Compare this to dominoes falling over: if the first one falls, the rest will fall too. Eventually the action potential reaches a synapse; communication between neurons takes place there.
The creation of an action potential happens in 1/1000th of a second, each time a neuron fires a stimulus. When the action potential is over, the sodium/potassium pump restores the original balance of sodium and potassium inside and outside the axon.
Some axons have a myelin sheath that has an insulating effect. In these nerves, action potentials can arise only at sites where the myelin is constricted. These places are called nodes of Ranvier. These nodes force the action potential to jump from node to node, allowing impulse conduction to proceed much faster than in unmyelinated nerves.
Author: Bart Aben (translated by Melanie Smekal)