Page 13, Early Development, Devel. Physiol., Dr. D. Penney

Cellular Development:

The development of skeletal muscle and cardiac muscle cells (fibers) differ in a number of ways (Figure 2.09): While skeletal muscle cells are derived from lateral plate mesoderm, cardiac muscle cells are derived from splanchnic mesoderm. Both types of cells increase in number by mitosis.

With synthesis of contractile elements (myosin, actin, etc.), skeletal muscle cells stop dividing, while cardiomyocytes continue. Skeletal muscle fibers attain their very large size (e.g. many cm in length) by fusion of individual cells into multinuclear myotubes.

Cardiomyocytes do not form myotubes. They may however becomes bi-, tri- or of a higher nuclearity by one or more terminal incomplete mitotic divisions.

Fibroblasts are also derived from splanchnic mesoderm.

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