Answer:
1. Isovolumetric contraction.
2. Ventricular filling.
3. Isovolumetric relaxation.
4. Ventricular ejection.
Explanation:
In Human anatomy, cardiac cycle can be defined as a complete heartbeat of the human heart which comprises of sequential alternating contraction and relaxation of the atria and ventricles, therefore causing blood to flow unidirectionally (one direction) throughout the human body.
Generally, the cardiac cycle occurs in two (2) stages;
Diastole : in this stage, the ventricles is relaxed and would be filled with blood.
Systole: at this stage, the muscles contracts and thus, allow blood to be pushed through the atria.
The following terms describe the electrical events with the correct phases of the cardiac cycle in mammals (human beings);
1. Isovolumetric contraction: The ventricular muscle cells depolarize at the start of this phase. During this phase, the pressure in the atria is lower than the pressure in the ventricles while the pressure in the arteries is higher than the pressure in the ventricles.
2. Ventricular filling: During this phase, Na+ entry through the funny channels causes the pacemaker potential of SA nodal cells to gradually become less negative until it reaches threshold. It causes the atria to contract at the end of the phase.
3. Isovolumetric relaxation: The ventricular muscle cells repolarize right before this phase. During this phase, all of the four (4) cardiac valves are closed while all of the four (4) chambers are relaxed.
4. Ventricular ejection: The cytosolic concentration of calcium in the contractile cells of the ventricle is highest during this phase. Also, the atrioventricular (AV) valves are closed while the semilunar valves are open.
