Sequence of events take place during action potential in brief

>In resting state, membrane is permeable to K⁺ and relatively impermeable to Na⁺.

>When a stimulus depolarize the membrane into the threshold value the voltage gated Na⁺ channels open, vastly increasing the membrane’s permeability to Na⁺.

>Na⁺ enters the cell across the membrane under the influence of both concentration gradient and the electric gradient.

>Na⁺ makes the membrane more depolarized and that makes more voltage gated sodium channels to open.

>As the membrane potential approaches equilibrium potential of Na⁺ the driving force of Na⁺ is reduced. Therefore less number of Na⁺ reach into the cell.

>After a short time the voltage gated Na⁺ channels are inactivated and stop the taken in of the Na⁺.  Here the membrane potential rise to +45mV.

>As this occurs, the voltage gated K⁺ channels open and greatly increases the permeability to K⁺ ions. Therefore K⁺ leaves the cell under the influence of concentration gradient and electric gradient.

>As K⁺ leaves, the positive charge inside the cell is reduced. After awhile the equilibrium potential of K⁺ is obtained and the membrane is hyperpolarized. Now the membrane potential is -75mV. Hyperpolarization is due to the delay of closing the K⁺ channels compared to Na⁺ channels.

>The voltage gated K⁺ channels close and by then the Na⁺ channels recovered by inactivation.