Question

Match the columns and find out the correct combination :

A. Resting phase	Activation gates of $N{a}^{+}$ open
B. Depolarizing phase	Inactivation gates open only
C. Repolarizing phase	Inactivation gate and activation gate of $N{a}^{+}$ is closed
D. Hyperpolarising phase	Both gates of $N{a}^{+}$ open

• A. A -2, B-1, C-4, D-3
• B. A -2, B-3, C-4, D-1
• C. A -2, B-1, C-3, D-4
• D. None of these

Answer 1

Answer: (A)

A -2, B-1, C-4, D-3

The formation of an action potential can be divided into five steps.

(1) A stimulus from a sensory cell or another neuron causes the target cell to depolarize toward the threshold potential.

(2) If the threshold of excitation is reached, all Na+ channels open and the membrane depolarizes. During this phase, the activation gate opens.

(3) At the peak action potential, K+ channels open and K+ begins to leave the cell. At the same time, Na+ channels close. The inactivation gate closes and the membrane begins to repolarise.

(4) The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire. (5) The K+ channels close and the Na+/K+ transporter restores the resting potential. When a cell is at rest, the activation gate is closed and the inactivation gate is open.

So, the correct option is 'A -2 B-1 C-4 D-3'.