Question #9e27c

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'.