CARDIAC MUSCLE – 1
Unlike skeletal muscle fibers, cardiac striated muscle fibers are short cylinders whose ends are relatively flattened and perpendicular to the cell axis.
Viewed in longitudinal sections, their cytoplasm shows transverse striation (bands) similar to those of skeletal muscle, although their striation is not always easily observed as in the skeletal muscle.
Each fiber has one or sometimes two nuclei placed in the center of the fiber, unlike skeletal muscle fibers whose nuclei are placed in the cell periphery. The central position of the nuclei can be best seen in longitudinal and in cross-sections.
A characteristic feature of their cytoplasm is the presence of thick transversal bands besides their regular striation. They are thicker and denser stained than the regular bands. They are junctional complexes called intercalated discs that are placed at the cell extremities connecting neighbor cells and creating rows of fibers. They are formed mainly by adherens and gap junctions. Unfortunately, they are not always easily observed in hematoxylin and eosin-stained sections, but are quite visible after the use of other stains.
In the heart, the fibers are organized into bundles organized in different directions.
In the lower figure: bundles of cardiac muscle fibers sectioned longitudinally.
Notice cigar-shaped nuclei placed in the cell center.
Viewed in longitudinal sections, their cytoplasm shows transverse striation (bands) similar to those of skeletal muscle, although their striation is not always easily observed as in the skeletal muscle.
Each fiber has one or sometimes two nuclei placed in the center of the fiber, unlike skeletal muscle fibers whose nuclei are placed in the cell periphery. The central position of the nuclei can be best seen in longitudinal and in cross-sections.
A characteristic feature of their cytoplasm is the presence of thick transversal bands besides their regular striation. They are thicker and denser stained than the regular bands. They are junctional complexes called intercalated discs that are placed at the cell extremities connecting neighbor cells and creating rows of fibers. They are formed mainly by adherens and gap junctions. Unfortunately, they are not always easily observed in hematoxylin and eosin-stained sections, but are quite visible after the use of other stains.
In the heart, the fibers are organized into bundles organized in different directions.
In the lower figure: bundles of cardiac muscle fibers sectioned longitudinally.
Notice cigar-shaped nuclei placed in the cell center.
As seen in longitudinal section
As seen in cross-section
Cardiac muscle in longitudinal section. Staining: HE. Small magnification.