Rectus Capitis Posterior Minor Muscle
Phases of the Cardiac Cycle
Phases of the Cardiac Cycle:
- As the ventricles relax from the previous cycle, blood passively flows into the ventricles from the atria through the open atrioventricular (AV) valves.
- Both atria contract (atria systole) to forcibly fill the ventricles with blood.
- The ventricles begin to contract (ventricular systole) after they are filled, which increases the intraventricular pressure. In response, the AV valves move upward and block blood from flowing back into the relaxing atria.
- The semilunar valves open due to continued ventricular contraction and rising intraventricular pressure. Blood enters the aorta and pulmonary trunk arteries and is then distributed through-out the body.
- After they contract, the ventricles enter a period of relaxation (ventricular diastole). The intraventricular pressure drops and blood in the large arteries reverses flow. This forces the semilunar valves to close, which prevents blood from entering the ventricles.
- The drop in ventricular pressure also allows the AV valves to re-open and a new cycle begins.