Overview of the system of<unk><unk>  which maintains the rhythmical contraction of the<unk> <unk>  signals arising in the SA node (located in the right atrium) stimulate the atria to contract. Then the signals travel to the atrioventricular node (AV node), which is located in the interatrial septum. After a delay, the<unk>  signal diverges and is conducted through the left and right bundle of His to the respective Purkinje fibers for each side of the<unk> , as well as to the endocardium at the apex of the<unk> , then finally to the ventricular epicardium; causing its contraction. These signals are generated rhythmically, which in turn results in the coordinated rhythmic contraction and relaxation of the<unk> . On the microscopic level, the wave of depolarization propagates to adjacent cells via gap junctions located on the intercalated disc. The<unk>  is a functional syncytium (not to be confused with a true "syncytium" in which all the cells are fused together, sharing the same plasma membrane as in skeletal muscle). In a functional syncytium,<unk>  impulses propagate freely between cells in every direction, so that the myocardium functions as a single contractile unit. This property allows rapid, synchronous depolarization of the myocardium. While advantageous under normal circumstances, this property can be detrimental, as it has potential to allow the propagation of incorrect<unk>  signals. These gap junctions can close to isolate damaged or dying tissue, as in a myocardial infarction<unk>  attack). Development Embryologic evidence of generation of the cardiac<unk>  system illuminates the respective roles of this specialized set of cells. Innervation of the<unk>  begins with a brain only centered parasympathetic cholinergic first order. It is then followed by rapid growth of a second order sympathetic adrenergic system arising from the formation of the thoracic spinal ganglia. The third order of<unk>  influence of the<unk>  is derived from the vagus nerve as the other peripheral organs form.
Electrical conduction system of the heart
Cardiac cycle
Coronary circulation
Parasympathetic nervous system
Myocardial contractility
Skeletal-muscle pump
Cardiac excitation-contraction coupling
Central chemoreceptors