Question

Assertion :In depolarisation process, there is a positive charge on the outer side of nerve fibres and a negative charge on its inner side Reason: During depolarisation, permeability of plasma membrane increases for sodium ions, so N$a^{+}$ ions move to outer side of the membrane and $K^{+}$ enter the nerve fibre

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is D Both Assertion and Reason are incorrect

During resting state or polarised state, there is negative charge on the membrane inside but when depolarization occurs, the permeability of membrane to sodium ions increases due to the opening of sodium gates, sodium ions diffuse rapidly into the neuron. The inside of the membrane becomes positively charged with respect to the outside. It is not possible for Na channel to open again without the repolarisation of a nerve fibre. Thus, movement of Na+ ions back from inside to outside is not possible. To compensate such a huge entry of Na+, the movement of K+ occurs from inside towards outside of cell through voltage-gated K+ channels.

Hence, the correct answer is (D)