Structure And Function Of The Cardiac Conducting System
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Heart beat
The heartbeat originates in the heart itself The auto-rythmic cells of the sino-atrial node (SAN) or pacemaker, located in the wall of the right atrium sets the rate at which the heart contracts
Control of cardiac muscle cell contraction
The timing of cardiac muscle cell contraction is controlled by impulses from the SAN spreading through the atria causing atrial systole They then travel to the atrio-ventricular node (AVN) located in the centre of the heart. Impulses from the AVN travel down fibres in the central wall of the heart and then up through the walls of the ventricles causing ventricular systole This is followed by diastole which is relaxation of the heart
Controlling heart rate
The medulla regulates the rate of the SAN through the antagonistic action of the autonomic nervous system (ANS) A sympathetic nerve releases noradrenaline which increases heart rate Whereas a parasympathetic nerve releases acetylcholine which decreases heart rate
Electrocardiogram
Impulses in the heart generate currents that can be detected by an electrocardiogram (ECG)