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Cardiac Muscle Tissue Forms a thick layer called myocardium. o Striated like skeletal muscle. o Contractions pump blood through the heart and into blood vessels. o Contracts by sliding filament mechanism. Cardiac muscle cells o Short o Branching o Have 1 or 2 nuclei and not fused o Triggered by ionic calcium to contract, like skeletal muscle. Cells join at intercalated discs o Complete junctions o Form cellular networks Cells are separated by the delicate endomysium o Bind adjacent cardiac fibers o Contains blood vessels and nerves. Intercalated Discs – Complex junctions Adjacent sarcolemmas intercalate Possesses 3 types of cell junctions o Desmosomes o Fasciae adherens – long desmosome-like junctions o Gap junctions. Triggered to contract by Ca2+ entering the sarcoplasm o Signals sarcoplasmic reticulum to release Ca2+ ions. Ions diffuse into sarcomeres Trigger sliding filament mechanism Not all cardiac cells are innervated o Will contract in rhythmic manner without innervation o Inherent rhythmicity Is the basic for rhythmic heartbeat Smooth Muscle Tissue • Found in the walls of visceral organs • Six major locations • Walls of circulatory vessels • Respiratory tubes • Digestive tubes • Urinary organs • Reproductive organs • Inside the eye • Cells are spindle-shaped • Contain one centrally located nucleus • Separated by endomysium • Grouped into sheets in walls of hollow organs • Longitudinal layer – muscle fibers run parallel to organ’s long axis • Circular layer – muscle fibers run around circumference of the organ • Both layers participate in peristalsis • Cells are non-striated and contain no sarcomeres • Thin and thick filaments are present • Entry of Ca2+ into the cytoplasm signals contraction of the smooth muscle fiber • Caveolae – tiny infoldings of the sarcolemma • Contraction is slow and sustained • • Takes 30 times longer to contract than skeletal muscle fiber • Maintains contractile force for a long time Is innervated by autonomic nervous system • Only a few smooth muscle fibers are innervated in each sheet • Impulse spreads through gap junctions • Whole sheet contracts as a unit • Exceptions – iris of the eye and arrector pili muscles