Cardiac physiology plateau phase. The remaining Ca for contraction is released from storage in the sarcoplasmic reticulum. The pattern of prepotential or spontaneous depolarization, followed by rapid depolarization and repolarization just described, are seen in the SA node and a few other conductive cells in the heart. Since the SA node is the pacemaker, it reaches threshold faster than any other component of the conduction system. It will initiate the impulses spreading to the other conducting cells. The SA node, without nervous or endocrine control, would initiate a heart impulse approximately 80–100 times per minute. Although each component of the conduction system
Cardiac neural crest cells OFT defects. Canonical Wnt signaling is especially important for cell cycle regulation of CNCC development and the initiation of CNCC migration. Non-canonical Wnt signaling plays a greater role in promoting cardiac differentiation and OFT development. Notch is a transmembrane protein whose signaling is required for differentiation of CNCCs to vascular smooth muscle cells and for proliferation of cardiac myocytes (muscle cells of the heart). In mice, disruption of Notch signaling results in aortic arch branching defects and pulmonary stenosis, as well as a defect in the development of the smooth muscle cells of the sixth aortic arch artery, which is