Question

Read the following statements:
a. Action potential propagates across the neuronal membrane.
b. Repolarisation decreases the responsiveness of neuronal membrane to further stimulus.
c. At the resting stage, the neuronal membrane is negatively charged on the inside and positively charged on the outside.
d. For every 2 $Na_+$ ions which are transported inside the cell, $Na_+$ -K= pump transports 3$k_+$ions to outside.

Choose the options which include correct statements only.
A. a & b
B. a & c
C. b & d
D. a & d

Answer 1

Hint: Conduction of nerve impulses happens across the synapse. It involves the following steps- Polarisation or the resting potential, depolarisation or the Action potential, repolarisation followed by re-factory period.

Complete Answer:
To solve this question, we must know about sodium potassium pumps across the neuronal membrane.
- The nerve cells transmit electrical impulses through action potential. It is the change in the charge of the membrane is due to the movement of ions to and fro of the neurons.
- The resting membrane potential of neurons depends on the types of ion channels. In neurons at the resting potential sodium and chloride ions are found in higher concentration outside the cell than the $k_+$ is present inside the cell. Thus resting potential is negative.
- In $Na_+$/$k_+$ pump 3 sodium ions move out of the membrane and 2 potassium ions move inside the membrane.
- The repolarization takes place due to the positive charge of sodium ion, the channel open. The $Na_+$ moves inward due to which the membrane potential increases. The potassium channel opens a little later. The potassium ion rushes out of the cell. This is called repolarisation. It decreases the responsiveness of the membrane for further stimulus due to the positive charge.

Thus the correct answer is (A).

Note: The concentration gradient is maintained by the action of sodium and potassium ion. It helps in maintaining the membrane potential. The resting potential of the membrane is around -50mv to -75mv.