Question

Question #9e27c

Answer 1

Here the analysis of the 3 phases, hope it helps!

Explanation:

Firstly, when the synaptic area of a neurone is yet to be polarized, means that this state is the resting potential .

Most sodium ions are actively transported out of the axon whereas potassium ions, into the cell cytoplasm. Here, there are also some negative ions (anions).

• Action potential is understood as a propagating wave of ion movements in & out of the axon membrane. [Polarization followed by depolarization repeatedly].

This impulse occurs when channels are opened in the neuron, having `Na^+` diffused in and `K^+` out. As a result, depolarization takes place. (`1^"st"` step)

The AP can be summarised in three stages or phases...

Depolarization:

As the sodium cations enter, the membrane of the stimulated cell reverses its polarity, turning the intercellular liquid negative relative to the inside.

Repolarization:

Once the electric gradient has reached the 'pinnacle' of excitement. The channels that let the `Na^+` channels through close up, while channels that allow `K^+` open, releasing these cations from the nerve cell.

Thus, it restores the localized negative membrane potential, bringing it back to its normal voltage.

Refractory Phase:

Shortly after the `Na` gates open, they close and go inactive. The gates cannot be opened again until the membrane is repolarized.

The `Na-K` pump returns `Na^+` to the outside and `K^+`in.
This area of the neuron membrane cannot be depolarized, setting up a 'rest period'.