How does the heart contraction and what controls Heart Rate (HR)?

Myogenic contraction mechanism of the heart: The heart is myogenic and so the heart beats due to electrical activity from inside the heart itself. This is compared to muscle that contracts due to signals from the Central Nervous System (CNS). The signals come from the sinoatrial node (SA node) in the upper wall of the right atrium which produces the pace-maker potential. These signals travel throughout the atria, causing them to contract. The impulses reach the Atrioventricular node (AV node) that is located at the bottom of the right atrium. The impulses are then sent down the atrioventricular bundle which carries the impulses down the centre of the heart (The hearts septum). The impulses then meet the bundle of Hs at the base of the heart and spread laterally to either side of the ventricles, causing the ventricles to contract.Autonomic control: When the impulses from the SA node reach the AV node, they are delayed for about a tenth of a second. This delays ensures that the atria are able to contract and fully relax before the ventricles contract, allowing the atria to fully empty and the ventricles to fill before ventricular contraction and blood ejection from the heart. For interest: Out of the body, but with constant blood supply, the heart would beat at around 100bpm at rest. However, inside the body, autonomic regulation permits the heart to beat at around 70bpm, due to parasympathetic vagal stimulation --> The 'rest and digest' mechanism.