Generation of the Action Potential

An axon is a relatively poor conductor, so that a graded potential is severely attenuated after traveling less than a millimeter. A different scheme is used for all long-distance transmission. The graded potential is translated into a series of voltage spikes, called action potentials (APs), each 100 mV high, that are continually regenerated. The number of spikes per second is roughly proportional to change in the original graded potential, so what we have is ?>frequency modulation ?>: the AP frequency constitutes the message. The AP discharge is characterized by a considerable amount of random ?>noise, ?> because it is initiated by ions that are constantly buffeted about in accordance with the kinetic theory of heat. The noise is not all bad; it is partly responsible for nonstereotyped behavior, an important ingredient of ?>creativity. ?> During an AP, sodium ions enter the axon while potassium ions leave. This migration is subsequently undone as the ions are pumped back via the expenditure of metabolic energy.