Heart contraction

Question

How the heart contraction is triggered?

Answer 1

Heart contraction is not dependent upon the neuronal stimulus though it may be modulated through the autonomous nervous system. Within the heart there exist pacemaker cells which are triggered themselves the action potentials which start the contraction of muscle. These cells are generally concentrated at the two special points of heart named as: the sinoatrial node (SA node), which is located within the superior portion of right atrium and the other is atrio-ventricular node (AV node) situated near to the interatrial septum. The action potentials produced through the depolarization of SA node cells proliferate cell to cell throughout the atria generating the atrial contraction. The atrial depolarization also disseminates to AV node which then transmits electric impulse to the ventricles by the specialized conduction bundles of interventricular septum and then to Purkinje fibers of ventricle walls causing ventricular contraction. The repolarization of SA node forms the atria relax and then the ventricles relax too.