You found the following in an experiment where you were testing refractory periods in a nerve preparation:
1. Keeping the usual stimulus strength, you could generate a 2nd action potential in the nerve if your stimulus frequency was every 5 milliseconds.
2. If you increased the stimulus strength, then you could generate a 2nd action potential with a second stimulus after 3 milliseconds.
3. If you used a stimulus frequency any faster than every 3 milliseconds, then you could not generate a 2nd action potential, irrespective of the stimulus strength you used.
Which of these conclusion is compatible with your experimental results in this nerve preparation?
A. The relative refractory period, where there are some voltage-gated Na+ channels that have closed again after being open for the action potential and inactivated, has a duration in this preparation of 2 milliseconds.
B. The absolute refractory period, when none of the voltage-gated Na+ channels have been through the stages of being inactivated and closed again, is 5 milliseconds in this preparation.
C. These results demonstrate why an action potential can travel in both directions when it is generated at the axon hillock, provided that a high frequency of stimulation is used.
D. The relative refractory period, with only some voltage-gated Na+ channels in the closed state again after the first action potential, has a duration of 8 milliseconds in this preparation.
E. The absolute and relative refractory periods are the same length, because voltage-gated Na+ channels are always in either an open or closed state.