Action Potentials

• When the neuronal membrane is at rest, the voltmeter reads a steady potential of approximately -65 mV, indicating that the inside of the neuron is negatively charged compared to the outside.

• The rising (overshoot) phase: the rapid depolarization of the membrane, which continues until Vm reaches a peak value of about 40 mV.

• The falling phase: the rapid depolarization of the membrane, until the inside of the membrane is actually more negative than the resting potential (after-hyperpolarization).

There are more Na+ ions on the outside of the cell than on the inside, and the neuron has negative electrical potential on the inside.