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crimsonkid85

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I have a question about some physiology concepts on the USMLE 1-- not sure if this is the right place to post. If it isn't--I'm sorry! :/ Without further ado...

Graph shows action potential in nerve cell. (Your simplest up down, Na action potential). Which of the following describes the membrane permeabilities of the region in the curve where repolarization is taking place (curve is coming down, phase 3), but the absolute value of the cell membrane potential is 0?

Permeability of Na>Permeability of K
PNa < PK
PNa approximately equal to PK

I have to admit, my concepts here are fuzzy. I know that generally, the idea behind repolarization is that K conductance must be greater than Na conductance for repolarization to take place. But then again, if a membrane potential is at equilibrium at 0mV, I also know that Na conductance has to be slightly greater than that of K conductance (because Na Nernst potential is like ~60mV while K Nernst potential is ~-90mV).

So then if the membrane potential is coming down, a la repolarization, but instantaneously, the cell membrane potential is 0mV, what is the permeabilities of Na relative to K?

Help, anyone?

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just re-read your question, not sure I answered it totally. But I would say that K & Na are at equilibrium at -20mV (-85 + 65 = -20mV) and since we're talking about 0 mV, then it should be more permeable to Na slightly. Pna > Pk
 
Did he mention he got an 800 on his first NBME and doesnt know what that means? Glad you got an 800 but dont know simple path or phys... Sounds SUSPECT
 
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