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electrical conduction system of the heart
The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to, and stimulate, the cardiac muscle (myocardium). The myocardium contracts after stimulation. It is the ordered, rhythmic stimulation of the myocardium during the cardiac cycle that allows efficient contraction of the heart, thereby allowing blood to be pumped throughout the body.
==Structure==
Electrical signals arising in the SA node (located in the right atrium) stimulate the atria to contract, and travel to the atrioventricular node (AV node), which is located in the interatrial septum. After a delay, the stimulus diverges and is conducted through the left and right bundle of His to the respective Purkinje fibers for each side of the heart, as well as to the endocardium at the apex of the heart, then finally to the ventricular epicardium.
On the microscopic level, the wave of depolarization propagates to adjacent cells via gap junctions located on the intercalated disk. The heart 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, electrical 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 electrical signals. These gap junctions can close to isolate damaged or dying tissue, as in a myocardial infarction (heart attack).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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