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Unformatted text preview: Cardiac Conduction Unlike skeletal muscle fibers (cells), which are independent of one another, cardiac muscle fibers (contractile muscle fibers) are linked by intercalated discs, areas where the plasma membranes intermesh. Within the intercalated discs, the adjacent cells are structurally connected by desmosomes, tight seals that weld the plasma membranes together, and electrically connected by gap junctions, ionic channels that allow the transmission of a depolarization event. As a result, the entire myocardium functions as a single unit with a single contraction of the atria followed by a single contraction of the ventricles. Action potentials (electrical impulses) in the heart originate in specialized cardiac muscle cells, called autorhythmic cells. These cells are self-excitable, able to generate an action potential without external stimulation by nerve cells. The autorhythmic cells serve as a pacemaker to initiate the external stimulation by nerve cells....
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- Spring '10