I can't recall the question at hand that you're talking about, but you're right in the sense of errors in books, and I think a lot of books have those types of issues. I remember doing a TPR example and for some reason I got stuck at one point in a circuits problem. And it took me hours until I realized that in fact the answer they had must have been mistyped. It pissed me right off because I was under the assumption that I was doing something wrong.
But even the AAMC has made fundamental mistakes. On AAMC 6, there's a question I think on the 2nd passage in regards to which to elements would form an ionic bond (CaI i think was the answer). I chose the correct answer according to the AAMC but when I went over it with my tutor, he pointed out that the answer is actually wrong because the differences in electronegativity made the bond actually covalent (less than 1.7 i think is covalent; anything over is representative of an ionic bond from what i recall).
Anyway, the prudent thing to do is crosscheck with other references.
EK wrote:As the electrochemical gradient of Na+ becomes greater, the force pushing the Na+ back into the cell also increases. The rate at which Na+ passively diffuses back into the cell increases until it equals the rate at which it is being pumped out of the cell. The same thing happens for potassium. When all rates reach equilibrium, the inside of the membrane has a negative potential difference (voltage) compared to the outside. This potential difference is called the resting potential.
Well said. It was section 4-11. EK was right. They were alluding to the fact that the resting potential is when the active forces balance out the passive forces. This is correct, although they fail to mention that it is really K+ that largely determines the resting membrane potential as Na+ is largely impermeable. K+ and Na+ ARE NOT at equilibrium at THE RESTING MEMBRANE POTENTIAL, and the chemical gradients WOULD NOT be maintained. However, the pump INDIRECTLY COUNTERACTS the movements of these ions to maintain a constant concentration inside and outside, so net effect is EQUILIBRIUM.
I don't think of this in this manner as taught by my mathematically oriented neuro class, but it's also correct. I just think that they make a grave mistake in not noting that it is really K+ that determines it. From their explanation, it seems as though Na+ is important, when it's really not. Finally, for the standard concentrations, K+ leaks out and Na+ leaks in (SLIGHTLY), if this were to continue, the concentration gradients wouldn't be maintained. This is what determines 80% of resting membrane potential.
However, this potential wouldn't be maintained because the concentrations wouldn't be maintained, so the Na+/K+ Pump acts to balance out the diffusion of Na+ in and K+ out to maintain the gradient and in effect the membrane potential. I think TPR has the best explanation, because they point this out. All this depth isn't needed, however, EK could have pointed a few things out. Sodium pump contributes little to RMP, but without it, you wouldn't have the potential because the Na and K ions would diffuse towards equilibrium.
