FIGURE 2.4 Electrical Changes During an Action Potential This graph shows the changing electrical charge of the neuron during an action potential. When the neuron depolarizes and ions cross the axon membrane, the result is a brief positive electrical impulse of +30 millivolts—the action potential. During the refractory period, the neuron reestablishes the resting potential negative charge of –70 millivolts and then is ready to activate again.