Cardiac pacemaker heart. There are 3 main stages in the generation of an action potential in a pacemaker cell. Since the stages are analogous to contraction of cardiac muscle cells, they have the same naming system. This can lead to some confusion. There is no phase 1 or 2, just phases 0, 3, and 4. The key to the rhythmic firing of pacemaker cells is that, unlike other neurons in the body, these cells will slowly depolarize by themselves and do not need any outside innervation from the autonomic nervous system to fire action potentials. As in all other cells, the resting
Cardiac neural crest cells the precursor to the pulmonary artery. In humans, mutations in Notch most often result in bicuspid aortic valve disease and calcification of the aortic valve. Bone morphogenetic proteins (BMPs) are required for neural crest cell migration into the cardiac cushions (precursors to heart valves and septa) and for differentiation of neural crest cells to smooth muscle cells of the aortic arch arteries. In neural crest–specific Alk2-deficient embryos, the cardiac cushions of the outflow tract are deficient in cells because of defects in neural crest cell migration. Fibroblast growth factor 8 (FGF8) transcription factors are essential for regulating the addition of