ABSTRACT
This chapter explores the interdependent roles of the various cell types that make up the heart. Individual calcium-tolerant myocytes isolated from the mature mammalian heart are widely used as an experimental system in cardiological research. The sinoatrial node, located at the entrance of the superior vena cava into the right atrium, contains myocytes that have special electrophysiological properties enabling them to generate spontaneously the electrical impulse responsible for heart contraction. Unmyelinated nerve fibers of the autonomic system, comprising collections of axons embedded within a highly convoluted Schwann cell, are commonly observed throughout the heart. Fibroblasts are common in the heart, scattered throughout its loose and dense connective tissue zones. Macrophages are irregularly shaped phagocytotic cells that reside in the loose connective tissue regions of most organs, including those of the heart. Macrophages originate predominantly from monocytes, though on occasion they may also arise by division of preexisting macrophages.
