Final answer:
The absolute refractory period is a time when no new action potential can be generated due to an inactivated Na+ channel, followed by the relative refractory period requiring a stronger stimulus for a new potential.
Step-by-step explanation:
The period of time when a membrane cannot respond to another stimulus, no matter how strong, is known as the absolute refractory period. During this time, an action potential cannot be generated because the voltage-gated Na+ channel is inactivated. After this period, there is a relative refractory period, during which a new action potential can only be initiated by a stronger stimulus than usual because voltage-gated K+ channels have not yet closed and the cell is experiencing repolarization.