control of heartbeat

cardiac muscle is myogenic - beat without any input from nervous system

- small changes in electrical charge of cardiac muscle = contraction

- cells are polarised when outside is -ve charged

- wave of depolarisation spreads from cell to cell = contract

heart beat starts at sinoatrial node - sends electrical impulses across walls of atria = start to contract, sends to other atria by bachman's bundle

atrioventricular valves walls stop electrical impulses reaching ventricles

impulses reach atrioventricular nodes and passed to the ventricles via bundle of HIS

bundle of His splits into 2 brances and carries the impulse by the purkyne fibres which carries down the ventricles

causes the ventricles to contract from the apex upwards - pushing blood out of heart