Step 1 – Resting Potential
Sodium and potassium channels are closed. Na+ rush into the cell; K+ are concentrated inside the cell. Potential difference: -85 mV.
Step 2 – Depolarization
Sodium channels open in response to a stimulus. Na+ rush into the cell according to the dictates of diffusion. Final potential difference +30 mV.
Step 3 – Repolarization
Na+ channels close and K+ channels open. K+ rush out of the cell according to the dictates of diffusion. Potential difference: slightly below -85 mV.
Step 4 – Resting Conditions Re-established
Na+ and K+ channels are closed. Sodium-potassium exchange pump moves Na+ out and K+ in. Resting potential difference: -85 mV.