Talk:Afterhyperpolarization

AHP, undershoot, and refractory period

What is the relationship between afterhyperpolarization, the undershoot phase, and the refractory period? It seems to me that people use them different ways, so the exact terminology is a bit confusing.

My impression is that AHP and the undershoot phase are equivalent. The AHP is partially responsible for the refractory period, and the AHP time period occurs within the refractory period. However, some people lump undershoot phase and refractory period together, so I don't know... Gaodifan (talk) 22:50, 20 September 2010 (UTC)

By the way, thank you for doing such a good job expanding this page from a stub!

As for your question, I noticed that issue too. The image treats the AHP as though it were the same thing as the refractory period, which it really isn't. We ought to ask Wikipedia:Graphic Lab for a revised version of the image, labeled correctly, which I'll try to do when I get around to it.

The answer to your question is that "afterhyperpolarization" and "undershoot" are, as you suspected, the same thing, with the former a more technical term. Both mean that the voltage goes more negative than baseline. But refractory period means the phase during which a second action potential cannot yet be initiated. The AHP is probably the single most important part of that (because voltage stays below threshold), but there are other mechanisms as well, such as voltage-dependent inactivation of sodium channels, that occur independently and have differing time courses. --Tryptofish (talk) 16:48, 21 September 2010 (UTC)