✅ ACTION POTENTIAL (Important)
1. Resting State:
- Charge Difference: At rest, the inside of a neuron is negatively charged compared to the outside. This resting potential is about -70 mV.
- Ion Distribution: There's more sodium Na+ outside the neuron and more potassium K+ inside.
2. Stimulus and Threshold:
- Threshold: A stimulus (like a signal from another neuron) can cause this charge to become less negative.
- Reaching Threshold: If the change is strong enough to reach a threshold (about -55 mV), it triggers an action potential.
3. Depolarization:
- Sodium Channels Open: Once the threshold is hit, special channels for Na+ open up, allowing sodium to rush into the cell.
- Charge Reversal: This influx makes the inside of the cell more positive, flipping the charge difference.
4. Peak:
- Maximum Positivity: The inside becomes very positive, up to +30 mV.
5. Repolarization:
- Sodium Channels Close, Potassium Opens: Sodium channels close, and potassium channels open, letting K+ flow out.
- Returning to Negative: The outflow of K+ makes the inside negative again.
6. Hyperpolarization:
- Temporary Excess Outflow: Sometimes too much potassium leaves, making it more negative than the resting state. This is temporary.
7. Refractory Period:
- Recovery Time: During this period, the inactivated sodium channels cannot be reopened, preventing any new action potential from being initiated.
- Restoring Resting State: Ion pumps work to restore the balance, bringing everything back to the resting potential.
