How does the sinoatrial node stimulate contraction? (4)

It sends out an electrical signal and is spread through the walls of the atria and then the walls of the ventricle = stimulates contraction of myocardium (heart muscle tissue) the impulse causes the atria to contract and stimulates another node between the atrium and ventricle 2nd node = atrioventricular node (AV) sends signals down the septum via Bundle of His Bundle of His supplies nerve fibres (purkinje fibres) in the ventricular wall = ventricular contraction