Question

When the cell membrane of a neuron is at a resting potential of -65 mV…

Select one:

A. Na+ ions tend to leak in through Na+ channels down their electrical gradient, but against their concentration gradient

B. Na+ ions tend to leak in through Na+ channels down their concentration gradient, but agains their electrical gradient

C. K+ ions tend to leak out through K+ channels down their concentration gradient, but against their electrical gradient

D. K+ ions tend to leak in through K+ channels down their electrical and concentration gradients

E. Na+ ions tend to leak out through Na+ channels down their electrical and concentration gradients

F. K+ ions tend to leak out through K+ channels down their electrical and concentration gradients

Answer 1

Answer: C. K+ ions tend to leak out through K+ channels down their concentration gradient, but against their electrical gradient

In the resting state, the membrane of a neuron has protein channels, called leak channels that allow Na+ or K+ to leak down their concentration gradients. Now the membrane faces more K+ leak than Na+ ion leak because it has more K+ leaky channels and hence is more permeable to potassium than sodium.

1. Now as the membrane potential is a negative value, it means that the inside of the cell has more negative charge Vs outside the cell.
2. Secondly the K+ ion concentration is more inside the cell.

Both these punts explains that whenever K+ leaks through the membrane, it has to move against the electrical gradient and along is concentration gradient.

Hence option C is the best choice.

NOTE: We could also say that option E for Na+ ion is also correct. Indeed it is true, but as explained above, the K+ ion is more prominent that Na+ ion leakage. Hence K+ takes an upper hand here and becomes more preferable ion.

Hope this helps. Please let me know if you have any query.

Best wishes!!