Conduction of action potentials

• Action potentials must be rapidly conducted over long distances in order for the nervous system to communicate with other cells. • Propagation of an action potential uses processes similar to those that generate the potential at the trigger zone. • a When a graded potential reaches threshold and triggers an action potential, a positive feedback cycle begins. • As voltage gated Na+ channels open, and Na+ions flood into the cell, this segment of the membrane depolarizes until its voltage is reversed. • At the peak of the action potential, the influx of sodium cause sodium gates in the adjacent segment of the membrane to open. • At the same time gated K+ channels are opening and Na+ channels are closing, repolarizing the original segment of the membrane and placing it in a refractory period. • During the refractory period a second action potential cannot be generated in this portion of the membrane. • However, the graded potential can depolarize to threshold in the segment in front, thus generating another action potential. • This cycle continues along the length of the axonal membrane from trigger zone to the axon terminals.

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