Question

Match the following stages of action potential to its corresponding state of ion movement

I. Depolarization stage (p). (K⁺) ions move outside the cell
II. Repolarization stage (q). (Na⁺) ions move inside the cell
III. Hyperpolarization stage (r). No net ion movement
IV. Resting stage (s). (K⁺) ions move into the cell
V. Threshold potential (t). Ligand gated sodium channels open
VI. Stimulus reaches the neuron (u). Voltage gated sodium channels open

• A. I. (p), II. (u), III. (q), IV. (r), V. (s), VI. (t)
• B. I. (q), II. (p), III. (s), IV. (r), V. (u), VI. (t)
• C. I. (s), II. (p), III. (p), IV. (t), V. (u), VI. (r)
• D. I. (p), II. (s), III. (r), IV. (u), V. (t), VI. (q)

Answer 1

The correct option is B I. (q), II. (p), III. (s), IV. (r), V. (u), VI. (t)

These are the stages of action potential:

1) When a neuron is in the resting state, it is polarized at a negative membrane potential of -70mV. However, during this state their is no net ionic movement because only Potassium leakage channels are open and potassium is in its electrochemical equilibrium and would not want to move in or out of the cell. The sodium ions would want to enter in, but would have no means to enter as there are no sodium channels open in the resting state of the neuron.

2) When a stimulus reaches the neuron, the ligand gated sodium channels open, causing a small initial depolarization. When the stimulus is large enough, more number of ligand gated sodium channels open causing (Na⁺) ions to enter the neuron to reach threshold potential of -55mV.

3) At threshold potential, voltage gated sodium channels open, allowing (Na⁺) ions to rush in along their potential gradient causing a complete depolarization of the neuron.

4) A while after voltage gated sodium channels open, that is at a higher voltage of about +30mV, which is the peak of the action potential, voltage gated potassium channels open and voltage gated sodium channels get inactivated. Then (Na⁺) stop moving in and (K⁺) ions rush out through the open channels due to the high positive potential inside the neuron, thus repolarizing the neuron.

5) Sometimes during this process, there might be an offset and the neuronal membrane might get hyperpolarized. During this stage potassium ions will move back into the neuron along its potential gradient, through the potassium leak channels to depolarize the membrane to a resting state.