So a recurring question that’s popped up is where exactly does absolute refractory period end and where does the relative refractory period begin and end on the AP waveform… It kinda depends, on who you ask.

…but there are also other versions, such as this:

or this, which is in between.

…really pretty much up in the air depending on the source material.

Below is images from each of those links:

Now… it depends on the type of channel as well and probability… so how do you decide? For the purposes of this class, as long as you understand what is occurring at the molecular level… ie, your Na+ channel inactivates… and while the majority of them are inactive, etc… you can’t get another AP, then you understand conceptually all you need to know. The closest diagram that I personally like, and I think is probably also closest to the book for this course, is the v1 image (1st image in the gallery). It gives a good approximation of probably where a lot of the majority of Na+ channels’ inactivation gates probably have popped open again once they’ve reached a negative enough potential… From there on out, relative refractory period! Just to review that, its where you have your delayed rectifiers still open… thus K+ is still flowing out. Remember, slow to open, slow to close (delayed kinetics). Thus, during your relative refractory period, you need a larger depolarization to probably get another AP spike.