Question

An action potential in the nerve fibre is produced when positive and negative charges on the outside and the inside of the axon membrane are reversed, because

• A. More potassium ions enter the axon as compared to sodium ions leaving it
• B. more sodium ions enter the axon as compared to potassium ions leaving it
• C. all potassium ions leave the axon
• D. all sodium ions enter the axon

Answer 1

Answer: (B)

more sodium ions enter the axon as compared to potassium ions leaving it

Answer 2

When a nerve fibre is stimulated, its membrane becomes more permeable to sodium ions; hence, more sodium ions enter the axon than potassium ions leaving it. As a result, the positive and negative charges on the outside and inside of the membrane are reversed. The membrane with reversed polarity is called depolarized.