This sequence of events results in a voltage pulse, called the action potential. (See Figure 3.) Only small fractions of the ions move, so that the cell can fire many hundreds of times without depleti...This sequence of events results in a voltage pulse, called the action potential. (See Figure 3.) Only small fractions of the ions move, so that the cell can fire many hundreds of times without depleting the excess concentrations of Na+ and K+. Although the impulse is due to Na+ and K+ going across the membrane, it is equivalent to a wave of charge moving along the outside and inside of the membrane.