Cardiac action potential action potential (see phase 2, below) and is a fundamental step in cardiac excitation-contraction coupling. There are important physiological differences between the cells that spontaneously generate the action potential (pacemaker cells; e.g. SAN) and those that simply conduct it (non-pacemaker cells; e.g. ventricular myocytes). The specific differences in the types of ion channels expressed and mechanisms by which they are activated results in differences in the configuration of the action potential waveform, as shown in figure 2. The standard model used to understand the cardiac action potential is that of the ventricular myocyte. Outlined below are the five phases of
Cardiac excitation-contraction coupling into the cell. Secondly Ca indirectly activates proteins, called myofilaments, resulting in muscle contraction. The two main myofilaments in cardiac (and skeletal) muscle are actin and myosin. Ca binds to a protein called troponin, which is bound to the actin filament. This binding causes a shape change in the troponin which exposes areas on the actin, to which the head of the myosin filament binds. The binding of the myosin head to actin is known as a cross-bridge. A molecule, called adenosine triphosphate (ATP) which is produced by an intracellular structure called a mitochondrion, is then used, as a source