Question

If we inject sufficient current into the giant axon of a squid, an action potential will result. Describe the chemical, electrical, and mechanical events that comprise the action potential, from its initiation to shortly after its termination.

Answer 1

Stages of Action potential

1. RESTING STAGE:
The membrane is in polarised state with potential in nerve .
Sodium and potassium channels are closed. Na+ are more outside the cell; K+ are concentrated inside the cell.

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.