BIOL 153 Lecture Notes - Cardiac Muscle Cell, Endoplasmic Reticulum, Atrioventricular Node
Document Summary
Like skeletal muscle, cardiac muscle is striated and contraction occurs using the same sliding filament mechanism. In contrast to skeletal muscle, cardiac muscle fibers are short, fat, branched and interconnected. Cardiac muscle fibers also have only one or two nuclei, contain more mitochondria, have fewer t-tubules, and much less sarcoplasmic reticulum. Adjacent cardiac muscle fibers are interlocked by finger like extensions called intercalculated discs. Desmosomes hold the cells together and prevent separation during contraction. Gap junctions allow the ions of the action potential to pass freely from cell to cell so that the whole heart contracts instead of just a few cells. Since all the cells of the heart are coupled electrically through gap junctions, it behaves as a single functioning unit or a functional syncytium. This is called autorhythmicity and these cells pace the heart. In skeletal muscles, impulses do not spread from cell to cell. As mentioned above, the cardiac muscle is an all or none effect.
