CARDIAC MUSCLE – 1
Unlike skeletal muscle fibers, cardiac striated muscle fibers are shaped like short cylinders whose ends are relatively flattened and perpendicular to the fiber axis.
When viewed in longitudinal sections, their cytoplasm shows transverse striation (bands) similar to that of skeletal muscle, although the striation is not always as easily observed as in skeletal muscle.
Each fiber has one or possibly two nuclei located in the center of the fiber, unlike skeletal muscle cells, whose nuclei are peripheral. The position of the nuclei can be best seen in cross-sections of the fibers.
A characteristic structure of cardiac muscle fibers is the presence of dark bands transverse to the cells. They are thicker and more strongly stained than the bands of regular striation. These are junctional complexes located in the cell membranes and indicate the fiber boundaries. They are composed of adherens junctions and gap junctions. They are called intercalated discs. Unfortunately, they are not easily observed in hematoxylin and eosin-stained sections, but they are quite visible with some other stains.
In the heart, the fibers are organized into bundles in different directions.
In the figure below: bundles of cardiac muscle fibers sectioned longitudinally.
Note the cigar-shaped nuclei located in the center of the cells.
When viewed in longitudinal sections, their cytoplasm shows transverse striation (bands) similar to that of skeletal muscle, although the striation is not always as easily observed as in skeletal muscle.
Each fiber has one or possibly two nuclei located in the center of the fiber, unlike skeletal muscle cells, whose nuclei are peripheral. The position of the nuclei can be best seen in cross-sections of the fibers.
A characteristic structure of cardiac muscle fibers is the presence of dark bands transverse to the cells. They are thicker and more strongly stained than the bands of regular striation. These are junctional complexes located in the cell membranes and indicate the fiber boundaries. They are composed of adherens junctions and gap junctions. They are called intercalated discs. Unfortunately, they are not easily observed in hematoxylin and eosin-stained sections, but they are quite visible with some other stains.
In the heart, the fibers are organized into bundles in different directions.
In the figure below: bundles of cardiac muscle fibers sectioned longitudinally.
Note the cigar-shaped nuclei located in the center of the cells.
Corte longitudinal
Corte transversal
Cardiac muscle. Staining: HE. Magnification: small.