The cells that carry nerve impulses are called neurons. Neurons have long conduits through which the impulses travel. A nerve impulse, as it conducts along a neuron, can be called an action potential<\/strong>. At the point of progress, the potential difference (aka voltage) swings from -65mV (rest potential) to +40mV (action potential) back to -65mV (rest potential).<\/p>\n The voltage refers to the potential difference across the cell membrane. It is managed by deployment of ions. The swing from -65mV to +40mV is accomplished by sudden controlled migration of Na+ ions into the cell. The return swing from +40mV to -65mV results from controlled departure of K+ ions. (The neuron controls when those ions can cross its membrane.)<\/p>\n After the action potential, the ions need to be reset so they are ready to propagate the next one. The Na+ ions are put back outside, while the K+ ions are brought back inside. This period can be referred to as the refractory period. The neuron may not be able to “fire” again until its completion.<\/p>\n HTH:)<\/p>\n Source:<\/p>\n Mader, Sylvia S. Inquiry into Life<\/u>, 9th Ed. Toronto: McGraw-Hill, 2000.<\/p>\n