MH 070 Cardiac Muscle Cells

Cardiac Muscle Cells

Cardiac muscle cells (cardiomyocytes) are intermediate in size between the large, multinucleated fibers of skeletal muscle and the smaller, spindle-shaped cells of smooth muscle.

Structural Organization:

• Cross-Sectional View:
  • Rounded to oval profiles, unlike the polygonal shape of skeletal muscle cells
  • Centrally located nucleus, unlike the multiple nuclei located at the periphery of skeletal muscle cells
• Longitudinal View:
  • Exhibit branching patterns creating a three-dimensional network
  • Relatively short cells that connect end-to-end, unlike the long, continuous fibers of skeletal muscle

Cellular Components:

• Nucleus: Single, round to oval nucleus positioned centrally within the cell
  • Binucleated Cells () Toggle Label Visibility : Often observed in larger cardiomyocytes
• Myofibrils: long arrays of sarcomeres identical to those found in skeletal muscle fibers
• Intercalated Discs () Toggle Label Visibility : Distinctive feature of cardiac muscle
  • Specialized intercellular junctions that appear as darkly stained transverse bands separating adjacent cells
  • Perpendicular to the long axis of the muscle fibers
  • Contain multiple types of intercellular junctions (desmosomes, adherens junctions, and gap junctions)
• Lipofuscin () Toggle Label Visibility : Yellow-brown granules that accumulate near the nucleus
  • Remnants of lysosomal digestion of cellular components that tend to increase with age
  • Few cells in this sample have detectable amounts

Functional Significance

• Myofibrils enable powerful, coordinated contractions
• Intercalated discs allow cardiomyocytes to function as a syncytium – a network of cells that contracts as a unified whole rather than as individual units
• Short, branching cells allow continuous wave-like contractions to propagate efficiently throughout the heart wall