Question

Describe the movement of Na⁺ and K⁺ in each event.

Events:

• Resting membrane potential
• Depolarization (rising phase)
• Falling phase
• Hyperpolarization

Answer 1

Stages of Action potential

1. RESTING MEMBRANE POTENTIAL 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 (falling):
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/. Hyperpolarization Stage: during this stage, the membrane becomes more negative than resting potential due to excessive efflux of K+ ion to outside and movement of sodium are still stopped due to closed Na+ channels

5. Resting Conditions Re-established
Na+ and K+ channels are closed. Sodium-potassium exchange pump moves Na+ out and K+ in.