Answer:
membrane potential reaches threshold
many voltage-gated Na+ channels open
Na+ ions rush into the cell
membrane potential rises
Explanation:
During resting condition, the axon membrane is polarized and has a voltage of -70mV. However, when action potential occurs after reaching the threshold level (voltage is equal to -55mV) after which the axon membrane first depolarizes and then polarizes again to reach the initial resting state. The threshold potential open the sodium voltage gates channels thereby allowing sodium ions to enter into the cell. As the sodium ion enters the cell, the membrane potential become less negative. When the membrane potential reaches the mark of +30mV, the sodium gated channels closes and potassium voltage gated channel opens.
