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Electrical events in the cardiac cycle

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Introduction

Electrical events in the cardiac cycle Normally, the atria and ventricles of the heart alternately contract and relax in a rhythmic fashion. This cycle of contraction and relaxation is controlled by the electrical conduction system of the heart. Therefore the cardiac cycle can be monitored by examining the electrical activity of the heart via an electrocardiogram (ECG). The cardiac cycle results in the rhythmic opening and closing of the valves of the heart. This activity produces heart sounds which also tell much about the functioning of the heart (as seen on a PCG-phonocardiogram). The Sinoatrial node (SAN) is spontaneously auto rhythmic (it contracts of its own accord). Also it is myogenic (has the ability to generate an electrical frequency) ...read more.

Middle

The general direction of the wave front created is from right to left and from the upper atria downward The waves spread out over the 2 atrial walls so that they contract. There is a band of fibres between the atria and ventricles, which have a high electrical resistance so the waves cannot spread from the atria to the ventricles. (Connective tissues-Fibro tendinous rings surrounding the valves cutting it into atria and ventricle sections) This electrical activity can be recognized as the P wave on an electrocardiogram. This electrical impulse results in contraction of the atria, pumping the blood into the ventricles. Takes 0.045 seconds to reach AVN. There is a delay, which allows time for the blood to flow from the atria into the ventricles. ...read more.

Conclusion

These branches provide routes for rapid conduction of the impulses throughout the interventricular septum and to the endocardial surface of the free ventricular walls. The terminal elements of this conduction pathway system are the Purkinje fibres. From Purkinje fibres, impulses penetrate to the interior of the ventricular myocardium, setting off a succession of depolarisations of sarcomeres and resulting in ventricular contraction. The depolarizing wave front progresses from endocardial to epicardial surfaces of the wall As the electrical impulse or depolarization spreads through the ventricles, it can be recognized as the QRS complex on an electrocardiogram. This electrical activity causes contraction of the ventricles, which is also known as ventricular systole. The spiral disposition of cardiac muscle sheets causes the spiral waves of contractions from systole for efficient basal squeeze, and the blood moves upwards, away from the spiral contractions. ...read more.

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