Question

The nerve fibre in its resting stage is

• A. more permeable to $K^{+}$
• B. semi-permeable to $K^{+}$
• C. less permeable to $K^{+}$
• D. All of the above

Answer 1

Answer: (A)

more permeable to $K^{+}$

Answer 2

In resting nerve fibre (a nerve fibre that is not conducting an impulse), sodium ions
$\left(N a^{+}\right)$predominate in the extra cellular fluid, whereas potassium ions $\left(K^{+}\right)$ predominate in the intracellular fluid (within the fibre). The plasma membrane is electrically positive outside and negative inside. This difference is called potential difference. The potentia difference across the plasma membrane is known as resting membrane potential. Both $N a^{+}$and $K^{+}$channels remain closed during resting membrane potential yet the membrane of the cell is moderately permeable to $K^{+}$and quite permeable to $K^{+}$and $C l^{-}$ions. Thus, potassium ions tend to diffuse out of the cell more easily than sodium ions diffuse in. This results in a higher concentration of cations outside the membrane compared to the concentration of cations inside it. This state of the resting membrane is called polarized state and makes its inner side electronegative to its outside.