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 muscle the walls of a house contain electrical wires and plumbing, cardiac muscle also contains specialised cells for conducting electrical signals rapidly (the cardiac conduction system), and blood vessels to bring nutrients to the muscle cells and take away waste products (the coronary arteries, veins and capillary network). Cardiac muscle cells or cardiomyocytes are the contracting cells which allow the heart to pump. Each cardiomyocyte needs to contract in coordination with its neighbouring cells to efficiently pump blood from the heart, and if this coordination breaks down then – despite individual cells contracting – the heart may not pump at all,