impulse starts in SA node/pacemaker, both atria contact (atrial systole), impulse reaches AV node and there is a short delay, before the impulse travels down the septum via the bundle of His, within the bundle of His are fibres called Purkyne fibres that cause ventricular systole from the base of the ventricles upwards, when blood has left the aorta the heart enters diastole before the cycle begins again.

control of heart rate task 2

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