Heart muscle cell. Coloured transmission electron micrograph of a heart muscle cell (cardiomyocyte), showing enormous numbers of mitochondria (brown), required for a constant energy supply to sustain heart muscle contractions. Myofilament proteins (cream), made up of mysosin and actin, enable the muscle to contract. All cardiomyocytes are joined end-to-end by special intercellular junctions. Gap junctions enable cell-to-cell electrical conduction which is the basis for the coordinated and rhythmic contraction of heart muscle.
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