Nodal and conducting tissue, atria, ventricles, and transition cells are all of muscle origin 2. Structure of these cells varies according to function. Nodal and conducting tissue have poorly developed contractile apparatus, the cells are small, and poorly connected by gap junctions. Transition cells connect conducting tissues to surrounding atria or ventricles. Their ultrastructure is intermediate to that of the nodal cells and the surrounding tissue.
Atrial cells are similar to, but smaller than ventricular cells.
Cells of the conduction system, bundle of HIS, bundle branches and purkinje system, exhibit numerous gap junctions and limited contractile machinery. Maximizes ventricular filling. Optimizes ventricular contraction by stabilizing valve leaflets and septum early in contraction. Maximizes ejection by synchronizing contractile activation in the ventricular wall. Action potential duration is 100x longer than in SKM or nerve with 4 distinct phases.