Ultrastructure of Mammalian Cardiac Muscle

The great majority of muscle cells of the mammalian heart are superbly organized entities. It is impressive to consider that observations on these myocytes are in most cases being made on cells which are roughly the same age as the entire animal; only a scant bit of evidence is yet available to suggest that any substantial capability for regeneration is intrinsic to the myocardia of higher vertebrates (see the section on Nuclei). Still these venerable cells can respond admirably under trying circumstances, such as those necessitating osmotic shrinkage or hypertrophy, in which cases they adjust their sarcolemmal and myoplasmic components to maintain an extraordinarily constant surface-volume ratio [1, 2]). In this chapter, we provide a sketch of the fine structure of cardiac muscle cells in mammalian heart. The many electron microscopic studies of such cells have served to point out the difficulty of making generalizations when considering the numerous aspects of myocardial substructure. We will, nevertheless, describe the salient features of myocardial cells, while pointing out along the way some of the variations on these basic themes which have been discovered to date.