Cardiac Action Potential
| Phase | Description | Mechanism |
|---|---|---|
| 0 | Rapid depolarisation | Rapid sodium influx |
| These channels automatically deactivate after a few ms | ||
| 1 | Early repolarisation | Efflux of potassium |
| 2 | Plateau | Slow influx of calcium |
| 3 | Final repolarisation | Efflux of potassium |
| 4 | Restoration of ionic concentrations | Resting potential is restored by Na+/K+ ATPase |
| There is slow entry of Na+ into the cell decreasing the potential difference until the threshold potential is reached, triggering a new action potential |
cardiac muscle remains contracted 10-15 times longer than skeletal muscle
| Site | Speed |
|---|---|
| Atrial conduction | Spreads along ordinary atrial myocardial fibres at 1 m/sec |
| AV node conduction | 0.05 m/sec |
| Ventricular conduction | Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles |
Myocardial action potential
Phase Description Mechanism
0 Rapid depolarisation Rapid sodium influx
These channels automatically deactivate after a few ms
1 Early repolarisation Efflux of potassium
2 Plateau Slow influx of calcium
3 Final repolarisation Efflux of potassium
4 Restoration of ionic
concentrations
Resting potential is restored by Na+/K+ ATPase
There is slow entry of Na+ into the cell decreasing the potential difference until
the threshold potential is reached, triggering a new action potential