he electrical impulses are what causes the hearts chambers to contract.
1) The process starts at the sino-atrial node. The node sends out waves of electrical activity to the atrial walls.
2) the waves cause the atria to contract but are stopped at the ventricles by non conducting collagen tissue.
3) Instead the impulse hits the atrioventricular node where there is a brief pause to make sure the atria contractions are complete.
4) The atrioventricular node passes the waves to the bundle of his (a bundle of muscles fibres) which conduct the waves to the finer muscle fibres.
5) The finer muscle fibres are called purkyne tissue which spread round the ventrical walls.
6) the waves cause the ventricular walls to contract simultaneously from the bottom up - to make sure no blood is left at the bottom.
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