Final answer:
The stages of the cardiac ventricular action potential in the correct order are depolarization, plateau, repolarization, represented on an ECG by the QRS complex, an extended plateau phase, and the T wave, respectively.
Step-by-step explanation:
The correct order of the stages of the cardiac ventricular action potential is depolarization, plateau, repolarization. This order corresponds to the following events:
- Depolarization: This is the phase where the ventricular muscle cells' membrane potential rapidly rises towards +30 mV, as a result of the influx of sodium (Na+) ions. This phase is represented on an electrocardiogram (ECG) by the QRS complex, indicating the ventricles are ready to contract.
- Plateau: This phase maintains the depolarized state due to the balance between the inflow of calcium (Ca²+) ions and the outflow of potassium (K+) ions. The plateau phase is critical for sustaining a prolonged contraction, which ensures effective blood ejection from the ventricles.
- Repolarization: During this phase, the membrane potential returns to its resting negative value as potassium ions flow out of the cell. This is represented by the T wave on an ECG and occurs after ventricular contraction, allowing the heart muscle to relax in preparation for the next heartbeat.
The depolarization of the atria, which precedes ventricular depolarization, is represented by the P wave. The repolarization of the atria is not visible on an ECG as it is masked by the QRS complex of the ventricular depolarization.