Jun 26, 2013
34
29
Status
The question reads:

If a neuronal membrane were to become suddenly impermeable to potassium ions but retain an active Na+/K+ ATPase, the neuron's resting potential would:
A) become more positive because potassium ion concentration would increase inside the neuron
B) become more positive because potassium ion concentration would increase outside the neuron.
C) become more negative because potassium ion concentration would increase inside the neuron.
D) become more negative because potassium ion concentration would increase outside the neuron.

The book says: A is correct. The sodium/potassium pump moves potassium inside the membrane. Potassium is positively charged making the inside of the membrane more positive. The resting potential is measured with respect to the inside.
-------------------------
I don't understand this for two reasons. The first reason is that the Na/K pump is a -1 charge mechanism so even though two K+ moves in, it must have pumped three Na+'s out; so my logic would be that the overall charge must decrease.

I also don't understand it with respect to the Question 30 that reads:

The Nernst equation, when used to determine the resting membrane potential of a neuron, indicates that, as intracellular K+increases, the membrane potential:
A) stays the same.
B) changes, but not in a predictable way.
C) becomes more positive.
D) becomes more negative.

I see these two questions asking essentially the same thing so shouldn't the answer be that it becomes more negative for both of them?

Thanks for the help
 

theonlytycrane

5+ Year Member
Mar 23, 2014
1,956
1,687
Status
Medical Student
For the first question I think the question is assuming that the Na+/K+ pump still works like normal, but that the K+ can't leak out once inside the cell. In that case the Na+ might come in later as normal, but K+ would also stay in there.

The second question aligns with your correct reasoning.
 
  • Like
Reactions: Member314159

wizzed101

The Little Prince
May 20, 2016
812
344
You are being asked about 2 different things. Membrane resting potential is determined mainly by permeability of each species of ion. The more permeable the more weight a type of ion has. In a normal cell, the permeability of K+ is about 100 times as high as that of Na+. This is why RMP is determined by K+.

For the second question, it is pretty straight forward Nernst equation question.
 
  • Like
Reactions: Member314159