group of cells in right atrium ( sino-atrial node ) is hearts pacemaker — controls electrical activity and so contraction rhythm of heart
generates A wave of excitation which spreads through the cardiac muscle so both atria contract together in atrial systole
Band of non-conductive collagen tissue prevents electrical conductivity passing directly to ventricles
Electricity transfers to the atrioventricular node and down bundle of His in the septum base of ventricles - travels up purkinje fibres so ventricles contract together
Rate sino-atrial notes fires controlled by medulla in brain - if doesn’t then a cardiac arrest can occur or irregular heartbeat