Neurogenic -2. mechanism of contraction are sliding filaments-*the mechanism of ca2+ regulation is different in smooth muscle than in skeletal muscle contractile characteristics of smooth muscle (10)similar to skeletal muscle, but contractile elements arranged differentlycontraction occurs due to myosin walking along actinca initiates contractiondifferences between single-unit, multi-unit smooth muscle and skeletal muscleneurogenic smooth muscle does not generate a muscle membrane apneural varicosities at multiple neuromuscular junctions along cell actin and myosin not arranged in sarcomeresboth filaments are longer than in skeletal muscle, actin more sono troponin associated w/ actindifferent myosin isoform than skel muscle w/ slower rate of contractionmyosin atpase activity much slowerslower cycling of myosin heads along actin filamentsmyosin light chain helps regulate contraction/relaxationsr less well developedamt/role of sr in ca release may vary between types of smooth muscleinternal ca stores in sr supplemented by extracellular ca ecf ca is concentrated in membrane invaginations called caveolaecaveolae are small invaginations of the smooth muscle sarcolemma that concentrate calcium (i.e., contain ca binding proteins)these are not the same as t-tubulesboth types contract very slowly due to low myosin head atpase activitycontraction can be sustained over long periods of timecontraction can continue even after ca removed from cytoplasmcontraction is much more efficient (less energy required per time)rate of x-bridge cycling drops way down during prolonged contractionlatch state myosin does not let go of actin allows smooth muscles to use
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