Question

What time period after the first action potential best describes the relative refractory period (the time when a second action potential can be generated only if the stimulus intensity is increased)?

1) 125-250 msec
2) 60-125 msec
3) 7.5 ms - 60 msec
4) less than 3.75 msec

Answer 1

The relative refractory period, a phase when a stronger stimulus is needed to trigger another action potential, occurs during the time frame of 7.5 ms to 60 msec after the first action potential.

Step-by-step explanation:

The time period after the first action potential that best describes the relative refractory period is best matched by option 3) 7.5 ms - 60 msec. During this period, a second action potential can only be generated if the stimulus intensity is increased. This increased threshold is due to the opening of voltage-gated K+ channels and the subsequent outflow of K+ ions, which partially counterbalances incoming Na+ ions, preventing immediate depolarization.

The absolute refractory period occurs before the relative refractory period and is a time when no additional action potential can be initiated, mainly due to the inactivation of the voltage-gated Na+ channels.