How is heart contraction triggered?
Heart contraction is independent from neuronal stimulus (although it can be modulated by the autonomous nervous system). In the heart there are pacemaker cells that trigger by themselves the action potentials that start the muscle contraction. These cells are concentrated at two special points of the heart: the sinoatrial node (SA node) situated in the superior portion of the right atrium and the atrioventricular node (AV node) situated near the interatrial septum.