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When a neuron is in resting state, i.e., not conducting any impulse, the axonal membrane is
A
Comparatively more permeable to $K^+$ ions and nearly impermeable to $Na^+$ ions
B
Comparatively more permeable to $Na^+$ ions and nearly impermeable to $K^+$ ions
C
Equally permeable to both $Na^+$ and $K^+$ ions
D
Impermeable to both $Na^+$ and $K^+$ ions
Detailed Solution
In the resting state the axonal membrane is comparatively more permeable to potassium ions ($K^+$) and nearly impermeable to sodium ions ($Na^+$).
It is also impermeable to the negatively charged proteins present in the axoplasm.
As a result the axoplasm has a high concentration of $K^+$ and a low concentration of $Na^+$, while the fluid outside has the reverse.
These gradients are maintained by the sodium–potassium pump, which transports 3 $Na^+$ outwards for 2 $K^+$ into the cell; the outer surface is therefore positively charged and the inner surface negatively charged (polarised membrane).
The membrane becomes freely permeable to $Na^+$ only when a stimulus is applied.
Hence at rest the membrane is more permeable to $K^+$ ions and nearly impermeable to $Na^+$ ions.
It is also impermeable to the negatively charged proteins present in the axoplasm.
As a result the axoplasm has a high concentration of $K^+$ and a low concentration of $Na^+$, while the fluid outside has the reverse.
These gradients are maintained by the sodium–potassium pump, which transports 3 $Na^+$ outwards for 2 $K^+$ into the cell; the outer surface is therefore positively charged and the inner surface negatively charged (polarised membrane).
The membrane becomes freely permeable to $Na^+$ only when a stimulus is applied.
Hence at rest the membrane is more permeable to $K^+$ ions and nearly impermeable to $Na^+$ ions.