The Heart

• Structure of cardiac muscle cells allows propagation of stimuli through the heart wall
• Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles
• There is a delay between the arrival and passing on of a stimulus at the atrioventricular node
• This delay allows time for atrial systole before the atrioventricular valves close
• Conducting fibres ensure coordinated contraction of the entire ventricle wall
• Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow