Page 309 - Atlas of Histology with Functional Correlations

SECTION 2 Cardiac Muscle

Cardiac muscle fibers are also cylindrical. They are primarily located in the

walls and septa of the heart and in the walls of the large vessels attached to the
heart (the aorta and pulmonary trunk). Similar to skeletal muscle, cardiac muscle
fibers exhibit distinct cross-striations because of regular arrangements of actin
and myosin filaments in the sarcomeres. Transmission electron microscopy
reveals similar A bands, I bands, Z lines, and the repeating sarcomere units. In

contrast to skeletal muscles, however, the cardiac muscle fibers exhibit some
important differences. The cardiac muscles develop by joining the cells end to
end through anchoring cell junctions called the intercalated discs that form the

distinguishing characteristic features of cardiac muscles. These dense-staining
discs are special attachment sites that cross the cardiac cells in a stepwise fashion
at irregular intervals. Cardiac muscles cells also exhibit only one or two central
nuclei, are shorter than the skeletal muscles, and exhibit branching (Fig. 8.9).

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