Cardiac muscle has the same types and arrangement of contractile filaments as skeletal muscle. Therefore, cardiac muscle cells and the fibers they form exhibit cross-striations evident in routine histologic sections. In addition, cardiac muscle fibers exhibit densely staining cross-bands, called intercalated, disks, that cross the fibers in a linear fashion or frequently in a way that resembles the risers of a stairway (Fig. 10.13). The intercalated disks represent highly specialized attachment sites between adjacent cells. This linear cell-to-cell attachment of the cardiac muscle cells results in "fibers" of variable length. Thus, unlike skeletal and visceral striated muscle fibers that represent multinucleated single cells, cardiac muscle fibers consist of numerous cylindrical cells arranged end to end. Furthermore, some cardiac muscle cells in a fiber may join with
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