Question

In resting stage of neuron, diffusion due to concentration gradient will drive

• A. $K^{+}$ into cell
• B. $K^{+}$and N$a^{+}$ out of cell
• C. N$a^{+}$ into cell
• D. N$a^{+}$ out of cell

Answer 1

Answer: (C)

N$a^{+}$ into cell

B. Na+ into cell

Reason: In the resting nerve fibre, higher concentration of sodium ions is found outside the cell, whereas inside the cell (intracellular fluid) potassium ions predominate. Due to this different concentration gradient, sodium ions tend to passively diffuse into the nerve fibre and potassium ions accuires the tendency of diffusing out of the nerve fibre down their electrochemical gradients. However, the membrane of a resting nerve fibre is more permeable to potassium than to sodium. Because of this selective permeability of the membrane, potassium leaves the nerve fibre faster than sodium enters it. This makes the membrane of the resting nerve fibre polarized, extracellular fluid outside it being more electropositive than the cell contents inside it. So the correct option is B.