Question

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

Hint:

Resting state → high \(K^+\) permeability
Action potential → sudden increase in \(Na^+\) permeability Resting potential is maintained mainly by potassium leak channels.

Answer 1

The Correct Option is A

Step 1: Recall the resting potential of a neuron. A neuron at rest maintains a resting membrane potential of about \(-70\,\text{mV}\), with the inside of the axon being negatively charged relative to the outside.
Step 2: Understand ion permeability at rest. At resting state:
The axonal membrane is highly permeable to \(K^+\) ions due to open potassium leak channels.
The membrane is nearly impermeable to \(Na^+\) ions because most sodium channels are closed. This selective permeability causes more \(K^+\) ions to diffuse out than \(Na^+\) ions to diffuse in, maintaining the negative resting potential.
Step 3: Eliminate incorrect options.
(B) Incorrect — sodium permeability is low at rest.
(C) Incorrect — permeability is not equal.
(D) Incorrect — membrane is selectively permeable, not impermeable.
Hence, the correct answer is \[ \boxed{\text{Comparatively more permeable to } K^+ \text{ ions and nearly impermeable to } Na^+ \text{ ions}} \]