Answer:
Explanation: The membrane potential returns to -70 mV after being depolarized and triggering an action potential through a process called repolarization. During depolarization, the membrane potential becomes more positive due to the influx of positive ions, such as sodium (Na+), through voltage-gated sodium channels.
To return the membrane potential to its resting state of -70 mV, repolarization occurs, involving the following steps:
Inactivation of voltage-gated sodium channels: As the depolarization reaches its peak, voltage-gated sodium channels become inactivated. This prevents further sodium influx.
Activation of voltage-gated potassium channels: Simultaneously with sodium channel inactivation, voltage-gated potassium channels start opening. These channels allow the efflux of potassium (K+) ions from the cell.
Potassium efflux: The open voltage-gated potassium channels allow potassium ions to move out of the cell, repolarizing the membrane. The movement of positively charged potassium ions out of the cell contributes to the restoration of the negative membrane potential.
Restoration of ion gradients: After repolarization, ion gradients across the cell membrane, maintained by ion pumps such as the sodium-potassium pump, are restored. The sodium-potassium pump actively transports sodium ions out of the cell and potassium ions into the cell, helping to reestablish the ion concentration gradients necessary for subsequent action potentials.
By repolarizing the membrane through potassium efflux and restoring ion gradients, the membrane potential returns to -70 mV, ready for subsequent action potentials to occur.