Answer
In the resting stage a neuron is polarized , that is, there is potential difference of -70mV between the outside of the neuron(axon) and the inside of the plasma membrane. An action potential is a rapid depolarization of the neuron which lasts for about 1mS and is propagated along a nerve fiber away from the soma.
An axon receives inputs from several hundred other neurons at any given instant; some of these are inhibitory and some are excitatory. In any case, the axon will decide to fire when the the stimulus( temporally or spatially summated) open voltage gated Na+ activation ion channel gates . If enough activation gates are opened , increased permeability of the membrane to Na+ ions will result in a sudden influx of sodium ions. This will decrease the negativity of the inside of the cell and the resting membrane potential of -70mV will rapidly become less negative. As more and more Na+ ions flow in, the potential will eventually reach the -50mV to -55mV range. At this level, threshold is reached and the process becomes self propagating. . The cell potential will eventually reach about +30mV. At this level the Na+ deactivation gates are deployed, the sodium channels close, and the K+ voltage gated channels open. The outflow of K+ ions and the cessation of the inflow of Na+ ions result in repolarization of the neuron.
Work Step by Step
The AP is triggered at the trigger zone when the inflow of Na+ ions into the neuron equals thsefflux of K+ ions from the cell(397)
