Page 314 - Atlas of Histology with Functional Correlations

between individual cardiac muscle fibers. The clear spaces between the

myofibrils represent the branching features of different cardiac muscle fibers.

FIGURE 8.13 Ultrastructure of cardiac muscle in longitudinal section. ×24,800.

Used with permission from Cui D. Atlas of Histology with Functional and
Clinical Correlations. Baltimore, MD: Wolters Kluwer/Lippincott Williams and
Wilkins; 2011.

FUNCTIONAL CORRELATIONS 8.3 ■ Cardiac

Muscle

Although the organization of the contractile proteins (actin and myosin) in
cardiac myofibers and their arrangement in sarcomeres is essentially the
same as in skeletal muscles, there are important differences. The T tubules
are located at the Z lines and are much larger than those in skeletal muscles.

Furthermore, the sarcoplasmic reticulum is less developed. Also, the
mitochondria are larger and more abundant in the cardiac cells indicating the
increased metabolic demands on the cardiac muscle fibers for continuous

function.

Cardiac cells are joined end to end by specialized, interdigitating
intercalated discs composed of fascia adherens, desmosomes, and gap
junctions. The gap junctions couple all cardiac muscle fibers and allow a

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