Cardiac Muscle Structure and Function

Cardiac Muscle Structure

• Cardiac muscle fibers are composed of many individual cells connected in series and in parallel with one another
• Dark areas crossing the fibers are intercalated discs, which are actually cell membranes separating individual cardiac muscle cells
• Intercalated discs fuse to form permeable communicating junctions (gap junctions) allowing rapid diffusion of ions

Function of Intercalated Discs

• Gap junctions enable ions to move easily in the intracellular fluid along the longitudinal axes of the cardiac muscle fibers
• Action potentials travel easily from one cardiac muscle cell to the next, past the intercalated discs

Syncytium of Cardiac Muscle Cells

• Cardiac muscle is a syncytium of many heart muscle cells, interconnected to allow rapid spread of action potentials
• When one cardiac muscle cell becomes excited, the action potential rapidly spreads to all others

Heart Composition

• The heart is composed of two syncytia: the atrial syncytium and the ventricular syncytium
• The atrial syncytium constitutes the walls of the two atria