Uber wrote:mangothecat wrote:
According to this site, the answer was A because "Depolarization of the plasma membrane occurs if there is an increase in the extracellular K+ ion concentration. Hyperpolarization would occur if the extracellular K+ ion concentration decreased, not increased."
I chose B because when the extracellular K+ ion concentration increases, the inside of the plasma membrane becomes more negative relative to the outside of the plasma membrane, causing hyperpolarization. Hyperpolarization occurs when the membrane potential becomes more negative. I assumed that the K+ ion concentration inside the cell stayed the same, and the concentrations of other ions also stayed the same. Where have I gone wrong?
Not very familiar with nervous yet, but I'm pretty sure that's where. The cell membrane is apparently fairly permeable to K+. Intracellular K+ will want to diffuse down its gradient, but it's also being attracted by intracellular anions, so the equilibrium is established: At RMP, there is 40x more K+ inside the cell than outside. Add extracellular K+ and reconsider the equilibrium. The anions stay the same, but there is less of a gradient, so K+ will want to diffuse less, and an intracellular buildup will occur. Therefore, K+ doesn't stay the same. So more positive inside means more positive voltage, meaning depolarization.
I know there's a detail or two somewhere that is wrong :/
I agree. This is a tricky question. I think you may have gotten it mixed up with IPSP's where K+ or Cl- channels open and K+ diffuses out or Cl- diffuses in. But in the case of IPSP's, the ions are moving while in the question you're just increasing the amount of K+ outside the cell so since what causes hyperpolarization is the K+ leaving the cell, you get depolarization in this case (the K+ ions aren't leaving so no accumulation of negative charge). Uber explained it correctly. Just remember that the cell is going to want to do whatever is most stable (like atoms), so if you disturb the equilibrium (#lechateliers) by adding more K+ outside the cell, the K+ will want to diffuse in through leakage channels (because remember the membrane is more permeable to K+), trying to restore RMP and this inward movement will mean more K+ ions so the inside will be more positive relative to the original charge inside (originally negative) (#journeay--> only lasa people will get this)