Answer:
1. depolarization
2. early repolarization
3. plateau
4. repolarization
Step-by-step explanation:
The cardiac myocyte action potential consists of four phases:
1. Phase 0 (depolarization): This phase is initiated by the opening of voltage-gated sodium channels, leading to a rapid influx of sodium ions into the cell. This rapid depolarization triggers the opening of more sodium channels, resulting in a positive feedback loop that rapidly depolarizes the cell membrane.
2. Phase 1 (early repolarization): This phase is a brief, partial repolarization caused by the inactivation of the sodium channels and the transient activation of potassium channels.
3. Phase 2 (plateau): This phase is characterized by a sustained, membrane potential that is maintained by a balance between inward calcium ion currents and outward potassium ion currents. The influx of calcium ions through voltage-gated calcium channels is balanced by the efflux of potassium ions through delayed rectifier potassium channels.
4. Phase 3 (repolarization): This phase is initiated by the closure of the voltage-gated calcium channels and the sustained activation of the delayed rectifier potassium channels. This leads to a rapid efflux of potassium ions, resulting in the repolarization of the cell membrane back to its resting potential.
These four phases of the cardiac myocyte action potential are essential for the proper functioning of the heart and are responsible for generating and regulating the electrical activity of the heart.