Resting Potential and Membrane Polarization — NEET Biology

Correct answer: A — S1, S3 and S5 are correct

The generation and conduction of a nerve impulse involve a series of changes in the membrane potential due to ion movements. S1: During the resting state, the neural membrane is indeed comparatively more permeable to K+ ions and nearly impermeable to Na+ ions. This statement is correct. S2: The sodium-potassium pump actively transports 3 Na+ outwards for 2 K+ into the cell, not the other way around. This maintains the ionic gradients and the resting potential. Therefore, this statement is incorrect. S3: When a stimulus is applied, the membrane becomes freely permeable to Na+, leading to a rapid influx of Na+ ions. This causes a reversal of polarity, where the outer surface becomes negatively charged and the inner side becomes positively charged. This statement is correct. S4: The electrical potential difference across the resting plasma membrane is called the resting potential, not the action potential. Action potential is the electrical potential difference across the plasma membrane at the site where polarity is reversed (depolarised). Therefore, this statement is incorrect. S5: Repolarisation, the restoration of the resting potential, is achieved by a rapid rise in permeability to K+ ions, which causes K+ to diffuse outside the membrane. This statement is correct. Based on the analysis, statements S1, S3, and S5 are correct. Therefore, option A is the correct answer.