Atlas of plant and animal histology

The image is from heart muscle.

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This image shows a section of the heart wall. Cardiomyocytes are observed in a longitudinal view. In the inset at the bottom, they are shown in a transverse view. The inset at the upper part shows a magnification of the section in longitudinal view.

Cardiac muscle cells, or cardiomyocytes, are much shorter than the skeletal striated cells. The limits between cardiomyocytes are dark strips known as intercalated discs. Intercalated discs are composed of different types of cell junctions such as desmosomes, adherent junctions, and tight junctions. They are dark because of the high protein concentration. Cardiomyocytes contain a nucleus, sometimes two, located in a central position of the cell. In the inset at the upper part, a pattern of dark and clear striations is observed, a consequence of the overlapping of the cytoskeleton filaments. Another difference, compared with the striated skeletal muscle cells, is that cardiomyocytes are branched cells.