A. Rapid sodium influx – Explanation
Electrical activity of the heart
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 |
NB cardiac muscle remains contracted 10-15 times longer than skeletal muscle
