22.7:
The Cardiac Cycle
The heart beats rhythmically in a sequence called the Cardiac Cycle, a rapid coordination of contraction, systole, and relaxation, diastole. An electrical signal sent from the sinoatrial node, near the right atrial wall causes both atria to simultaneously contract and push blood into the ventricles.
When the pulse reaches the atrioventricular node between the right atrium and right ventricle, it pauses for approximately a 1/10th of a second which allows blood to completely empty from the atria.
The charge then spreads through the Bundle of His, down the intraventricular septum by way of the right and left bundle branches and then through the walls of the ventricles’ Purkinje fibers inducing ventricular contraction and pumping blood out of the heart and into the pulmonary artery and aorta.
Meanwhile, the atria which are in diastole, continue to be filled with blood. As the ventricles relax, the blood pours down into the ventricles and the cycle continues.
22.7:
The Cardiac Cycle
The heart beats rhythmically in a sequence called the cardiac cycle—a rapid coordination of contraction (systole) and relaxation (diastole).
The Process
Electrical signals—sent from the sinoatrial (SA) node in the right atrial wall to the atrioventricular (AV) node between the right atrium and right ventricle—cause both atria to simultaneously contract. When the signal reaches the AV node, it pauses for approximately a tenth of a second, allowing the atria to contract and empty blood into the ventricles before they contract.
The electrical impulses are then conducted by the bundle of His and propagated to the left and right bundle branches. The signal is then conducted by Purkinje fibers in the ventricular walls, inducing ventricular contraction and pumping blood out of the heart.
During diastole (relaxation), the heart fills with blood, and the cycle is repeated.
Suggested Reading
Troiani, Diana, and Ermanno Manni. "The Work by Giulio Ceradini in Explaining the Mechanism of Semilunar Cardiac Valve Function." Advances in Physiology Education 35, no. 2 (June 1, 2011): 110–13. [Source]
Ho, Ivan Shun. "Visualizing the Cardiac Cycle: A Useful Tool to Promote Student Understanding." Journal of Microbiology & Biology Education: JMBE 12, no. 1 (May 19, 2011): 56–58. [Source]