Cardiac pacemaker ventricles, within the atrial septum. If the AV node also fails, Purkinje fibers are occasionally capable of acting as the default or "escape" pacemaker. The reason Purkinje cells do not normally control the heart rate is that they generate action potentials at a lower frequency than the AV or SA nodes. Cardiac pacemaker The contraction of cardiac muscle (heart muscle) in all animals is initiated by electrical impulses known as action potentials. The rate at which these impulses fire controls the rate of cardiac contraction, that is, the heart rate. The cells that create these rhythmic impulses, setting the pace
Cardiac neural crest cells and GATA families of molecules. In addition to these signaling pathways, these processes are also mediated by environmental factors including blood flow, shear stress, and blood pressure. The CNCCs interact with the cardiogenic mesoderm cells of the primary and secondary heart fields, which are derived from the cardiac crescent and will give rise to the endocardium, myocardium, and epicardium. The CNCCs themselves are the precursors to vascular smooth muscle cells and cardiac neurons. For example, CNCCs are required for the formation of the aorticopulmonary septum (APS) that directs cardiac outflow into two tracts: the pulmonary trunk and the aorta of