Question

In a nerve if sodium pump is blocked, which of the following is most likely to happen?
a. $Na^+$ and $K^+$ will increase outside the cell
b. $Na^+$ outside the nerve will increase
c. $Na^+$ inside the nerve will increase
d. $K^+$ inside the nerve will increase

Answer 1

The ionic gradient is maintained by the active transport of ions with the help of the $Na-K$ pump. The $Na-K$ pump brings 3 $Na^+$ outside the nerve cell and 2 $K^+$ inside the nerve cell. If a nerve in this $Na-K$ pump is blocked, there will be no movement of ions inside or outside the nerve cell and the concentration of ions will increase.

Complete answer:
• The function of the $Na-K$ pump is to maintain the potential of the cell membrane, to maintain the low concentration of sodium ions and a high concentration of potassium ions inside the cells. This gradient is maintained by active transport of these ions and for this transportation, it requires $Na-K$ ATPase enzyme.
• This pump brings 3 sodium ions outside the cell and 2 potassium ions inside the cell. During this activity of the pump more positive charge will accumulate towards the outside of the cell and a more negative charge will accumulate towards the inner side of the cell.
• This process occurs during the resting phase (when the stimulus is not given).
•This from the above mechanism of the $Na-K$ pump, it is clear that if there is a blockage of the sodium pump in a nerve cell then the transport of ions stops and the concentration of sodium ions inside the nerve cell will increase as these ions will keep on accumulating.

Hence, the correct answer is option (C).

Note: During depolarisation, when a stimulus is given the sodium pump stops to work which causes the flow of sodium ions inside the cell. In this way, more positive charges are accumulated inside the cell and more negative charges accumulate outside the cell.
When the stimulus is removed it is called repolarisation in which again the pumps start to work.