BIO Self-Assessment #74

[regeneration]

Advertisement - Members don't see this ad

The question is asking about the nature of the voltage gated Na+ and K+ gates during an action potential repolarization phase.

The answer is that Na+ gates are closed and K+ gates are open. In the description of the solution, it says that Na+ gates are open and K+ gates are closed during depolarization, and that K+ gates are open and Na+ gates are closed during depolarization.

I was under the impression that both gates open at the start of an action potential, but that K+ opens & closes more slowly; I thought that the Na+ gate closes during repolarization, but the membrane repolarizes because permeability to potassium is > permeability to Na+ during repolarization.

Can someone clarify this for me?

 

[image187]

The question is asking about the nature of the voltage gated Na+ and K+ gates during an action potential repolarization phase.

The answer is that Na+ gates are closed and K+ gates are open. In the description of the solution, it says that Na+ gates are open and K+ gates are closed during depolarization, and that K+ gates are open and Na+ gates are closed during depolarization.

I was under the impression that both gates open at the start of an action potential, but that K+ opens & closes more slowly; I thought that the Na+ gate closes during repolarization, but the membrane repolarizes because permeability to potassium is > permeability to Na+ during repolarization.

Can someone clarify this for me?

There are more than 1 type of ion channel for each ion. The voltage gated channels responsible for the flux of ions during the action potential are not the same channels that allow ions to maintain the resting membrane potential by passively diffusing down their gradients (which are maintained by the Na/K pump). During the resting phase, THESE passive ion channels are the ones where the permeability is important. Potassium is allowe to diffuse out more than sodium is allowed to diffuse in, holding a net negative charge inside the cell. The actual AP has a few different phases which you should look up because it might make more sense. Basically, there are "delayed opening" voltage gated-potassium channels (which you may be thinking of) that open soon after the voltage gated Na channels have let most of the Na rush in and create the huge positive upswing of the potential. The sodium channels become locked shut and inactivated and the K channels then end up letting out a bunch of potassium for the downswing of the potential to. Essentially, for the rise of the AP, Na channels are open and K are closed. For the fall, K are open and Na are closed