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20081006 - PNB 250 Page#1 Lecture15 Smooth Muscle...

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PNB 250 Page # 1 Lecture15 Smooth Muscle *actin-myosin crossbridge activity same as skeletal muscle Review *cells lack striations and innervated by autonomic n.s. *precursor cells remain single cells – single nucleus *size, 2-10 μ m (much smaller than skeletal muscle fibers) t-tubules not necessary Myofilaments in smooth muscle 1. actin 2. myosin anchored to plasma membrane by “dense bodies” α -actinin (same as z-line) 3. cytoskeletal filaments (elastic framework) a. myosin 1/3 that of skeletal muscle b. actin 2X that of skeletal muscle c. 2 actins to 1 myosin in skeletal muscle d. 10-15 actins to 1 myosin in smooth muscle Result: more chaotic overlap actins are oriented toward long axis of cell no sarcomere structure mysin crossbridges all go in same direction in SM Length-tension relation differs tension length skeletal muscle smooth muscle
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PNB 250 Page # 2 Smooth and skeletal muscle develop the same amount of tension per unit cross-sectional area – but smooth muscle can maintain tension over a greater length. This is due to the a.
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