Question

Describe in detail the steps/mechanism for generating an action potential.

Answer 1

1. RESTING STAGE:

The membrane is in polarised state with potential in nerve about - - 85mV.

Sodium and potassium channels are closed. Na+ are more outside the cell; K+ are concentrated inside the cell. Potential difference: - 70mV.

2. Depolarization STAGE:

When local potential touches the threshold level it opens up sodium channel in the membrane causing abrupt rising of membrane potential towards positivity. It overshoot beyond the zero level and become positve.

This is because of entry of Positive Sodium ions into the cell

3.Stage of Repolarization:

Within fractions of second the sodium channel begins to close and potassium channels open up causing diffusion of positive potassium to outside the cell.

This results in decreasing of membrane potential towards negativity.

4. Resting Conditions Re-established

Na+ and K+ channels are closed. Sodium-potassium exchange pump moves Na+ out and K+ in. Resting potential difference: -85 mV

Role of Sodium voltage gated channels:

These channels are essential for Depolarization stage.

If these channels are blocked, the Depolarization will not occur and the nerve will be hyperpolarised.

If these channels are stimulated then it results in more rapid functioning of the nerve.

Role of potassium voltage gated channels :

These channels are essential for Repolarization of the nerve potential

If the get blocked the nerve will be in sustained state of Depolarization.

If these channels are stimulated. Action potential will cease more rapidly and there will occur a hyperpolarization state.