MH 054 Cardiac Muscle

Cardiac Muscle

Cardiac muscle is striated, involuntary muscle found in the heart wall. Cardiac muscle cells (or cardiomyocytes) contain the same contractile filaments as in skeletal muscle.

• Cross-Section
  • Cardiac muscle cells - have rounded cross-sections (less than 25 µm in diameter) with a centrally located nucleus.
• Longitudinal Section - cardiac muscle cells are smaller in size than skeletal muscle (50 to 250 µm in length)
  • Branched Cells - cells are joined end-to-end and are often branched
  • Nuclei - cells have a single or occasionally two centrally located nuclei
  • Intercalated Discs - specialized junctions that connect the individual cells. They are usually unstained, but occasionally appear as thin, dark line between adjacent cells. The intercalated discs are perpendicular to the direction of muscle fibers. They are best seen when stained with phospho-tungstic acid (MH 056 Muscle Types).
  • Lipofuscin Pigment - residue of lysosomal digestion that accumulates as yellow-brown granules near the nucleus of some cells.

Cardiac muscle does not contain cells equivalent to the satellite cells of skeletal muscle.

The ultrastructure of cardiac muscle cells is seen in cross-section in EM 133 Cardiac Muscle and longitudinal section in EM 137 Cardiac Muscle by transmission electron microscopy. The structure of intercalated discs is also seen in EM 122 Cardiac Muscle.