Question 31

[anon3543]

31. In Figure 1, the period from the peak membrane potential to the lowest membrane potential is referred to as the:

1. absolute refractory period. [x]
2. relative refractory period. [x]
3. depolarization period. [x]
4. hyperpolarization period. [x]

INCORRECT:
Your Answer: B
Correct Answer: A

Explanation
The period from the peak membrane potential to the lowest membrane potential is the time during which the membrane can no longer depolarize and is referred to as the absolute refractory period (BIO 5.1.2). During this time, the cell polarizes back to the initial negative membrane potential so that the next action potential can occur. Quickly following this period, the cell has the ability to depolarize but with some difficulty. This is referred to as the relative refractory period.


My concern: From what I understand, the absolute refractory period is due to the inactivated Na+ channels (thus having no hope whatsoever of being stimulated again), and this occurs from the beginning of the action potential to somewhere between the two peaks. The relative refractory period is due to the continued outward diffusion of K+ (hyperpolarization), and so I thought that was better encompassed (I would envision it to start around the threshold voltage on down and back up to the resting potential again). Anyways, maybe that was too picky, but you can decide what is best. Thanks.

[admin]

You clearly have very strong biological sciences skills: that's very good! You are partly correct. Answer choice A is still the best answer.

You can see a good graph here: www.colorado.edu/kines/Class/IPHY3430-200/image/figure0413.jpg

[dnpgr16513]

Hi,

Why isn't the answer D? I assumed that right after the cell has depolarized, it goes back to polarizing again. Since the questions states to the lowest membrane potential I always thought this is hyperpolarization. Can you explain this more?

thanks!

[jsfkt78927]

i with you dnpgr, but the only argument for the correct answer is that the question asks for the period. Which is a small detail, but important because hyperpolarization is simply just hyperpolarization and is rarely called hyperpolarization period, if ever (imo). I was going a little too quickly and didnt notice these small differences.

So it follows that refractory period describes the time or period of the graph.

I guess the question could have asked, 'In Fig. 1, the region of the graph where the cell potential dips below resting membrane potential is referred to as the:'

my 0.02 $