A nerve impulse is a message which is transmitted along a nerve fiber or axon. It originates in the neuron's soma, or cell body, passes into the axon hillock, and then speeds down along the axon until it reaches the axon terminal or synaptic knobs. The impulse must then make its way across a gap called the synapse, to stimulate another neuron's or muscle cell's soma.

The nerve impulse occurs due to changes in the electrical charge along the axon. Normally, at rest, the chemical makeup of the axon's membrane allows the inside of the membrane to be slightly more electrically negative compared to the slightly more positive outside of the membrane. This condition is maintained by the presence of various channels or pumps within the membrane which work to maintain a particular proportion of potassium and sodium molecules on the inside and the outside of...