Question

Fill in the correct sequence for generation of Action potential in a neuron

Stimulus ⟶Inflow of $N{a}^{+}$ ions ⟶ _(i)_____⟶Repolarisation ⟶___(ii)______

• A. (i) Transmission of $N{a}^{+}$, (ii) Inflow of $N{a}^{+}$ ions
• B. (i) Inflow of $N{a}^{+}$ ions, (ii) Transmission of $N{a}^{+}$
• C. (i) Transmission of $N{a}^{+}$ & $K^{+}$ , (ii) Hyperpolarization & RMP
• D. (i) Hyperpolarization, (ii) Inflow of $N{a}^{+}$ ions

Answer 1

The correct option is C

(i) Transmission of $N{a}^{+}$ & $K^{+}$ , (ii) Hyperpolarization & RMP

The correct sequence of Action Potential is:

1. Stimulus: A stimulus arrives at a neuron synapse.

2. Inflow of $N{a}^{+}$ ions: The permeability of membrane to $N{a}^{+}$ is greatly increased at the point of stimulus (rapid influx of $N{a}^{+}$) and $N{a}^{+}$ enters the neurons through ligand-gated channels.

3. Transmission: The influx of $N{a}^{+}$ ions causes membrane depolarisation which opens the voltage-gated $N{a}^{+}$ channels, causing high influx of $N{a}^{+}$. Opening of the voltage -gated channels causes a positive cascade that is transmitted along the axon. Thus an action potential is generated.

4. Repolarisation: The depolarisation of membrane during action potential causes opening of voltage-gated $K^{+}$ channels and a cascade efflux of $K^{+}$ ions. Meanwhile the voltage-gated $N{a}^{+}$ channels close. These two processes together causes repolarization of the neuron membrane.

5. Hyperpolarisation and RMP: The voltage-gated $K^{+}$ channels begin to close as the membrane potential reach the resting state. However, their activity causes a slight dip below the resting membrane state, and is called hyperpolarisation. And although there is slight dip in the membrane potential soon after an action potential, the resting channels (leakage channels) ensures that the resting membrane potential is regained soon.