Work Step by Step
All action potentials are of the same magnitude. Each action potential peaks at +30 mV; the action potential cannot get any higher because once it reaches a particular voltage, the voltage-gated sodium channels close and the voltage-gated potassium channels open, allowing potassium ions to travel out of the cell down its concentration gradient. This causes a reduction in the membrane potential. Because the positive potassium ions move out of the cell, the membrane potential decreases to a little below the resting potential. Potassium ions quickly diffuse from the cytoplasm, and the amount of potassium ions are returned to normal conditions, thus restoring the resting potential.