Describe the structure and function of cardiac muscle, commenting on the type and source of nervous stimulation cardiac muscle receives. What occurs where two cardiac muscle cells meet end to end?
Cardiac muscle forms the tissue of the heart and shares characteristics from both striated and smooth muscle: Cardiac fibers are striated as are the fibers of striated muscle, but cardiac fibers are stimulated by specialized cardiac muscle cells that spontaneously produce signals; the intrinsic rhythm of contraction of the heart can be modified by the autonomic nervous system. At the point where two cardiac cells meet end to end, their cell walls become very closely fused. The junction is called an intercalated disc. Cardiac muscle cells are also connected by gap junctions, openings which allow the flow of ions between the cells. Such ionic current is the means by which action potentials are propagated among cardiac muscle cells.
