Question

2. List sequence of electrical cardiac events.

Answer 1

The heart possesses the property of autorhythmicity, which means it generates its own electrical impulses and beats independently of nervous or hormonal control.

SINOATRIAL NODE (SA NODE) :

This small mass if specialised cells lies in the wall of the right atrium near the opening of the superior vena cava. The sinoatrial cells generate these regular impulses because they are electrically unstable. Because the SA node discharges faster than any other part of the heart, it normally sets the heart rate and is called the pacemaker of the heart.

ATRIOVENTRICULAR NODE (AV NODE) :

Normally, the AV node merely transmits the electrical signals from the atria into the ventricles. There is a delay here, the electrical signal takes 0.1 of a second to pass through into the ventricles. This allows the atria to finish contracting before the ventricles start. The AV node also has a secondary pacemaker function and takes over this role if there is a problem with the SA node itself, or with the transmission if impulses from the atria.

ATRIOVENTRICULAR BUNDLE (AV BUNDLE OR BUNDLE OF HIS) :

This is a mass of specialised fibres that orfinate from the AV node. Within the ventricular myocardium the branches break up into fine fibres, called the purkinje fibres. The AV bundle, bundle brances and purkinje fibres transmit electrical impulses from the AV node to the apex of the myocardiam where the wave of ventricular contraction begins, then sweeps upwards and outwards, pumping blood into the pulmonary artery and the aorta