Heart arrhythmia muscle cell firing off an impulse on its own. All of the cells in the heart have the ability to initiate an action potential; however, only some of these cells are designed to routinely trigger heart beats. These cells are found in the conduction system of the heart and include the SA node, AV node, Bundle of His and Purkinje fibers. The sinoatrial node is a single specialized location in the atrium that has a higher automaticity (a faster pacemaker) than the rest of the heart and, therefore, is usually responsible for setting the heart rate and initiating each heart
Muscle contraction either excitatory (contractile) or inhibitory (relaxing). There are two types of cardiac muscle cells: autorhythmic and contractile. Autorhythmic cells do not contract, but instead set the pace of contraction for other cardiac muscle cells, which can be modulated by the autonomic nervous system. In contrast, contractile muscle cells (cardiomyocytes) constitute the majority of the heart muscle and are able to contract. Unlike skeletal muscle, excitation–contraction coupling in cardiac muscle is thought to depend primarily on a mechanism called calcium-induced calcium release. Though the proteins involved are similar, the L-type calcium channels and ryanodine receptors (RyRs) are not physically coupled. Instead,