Lecture 17 – Muscle Physiology V

The disadvantage is offset b increased mobility when

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Why the disadvantage? The disadvantage is offset b increased mobility When the biceps shortens by 1 cm, the load moves 7 cm Therefore the velocity of the hand is &x that of the biceps shortening Smooth Muscle Physiology Every smooth muscle cells is spindle shaped with a diameter of 2-10 microns and length  in the range of 10-100 microns Many different types with other stimulation Found around hollow organs Some have gap junctions for mass stimulation, others have singular stimulation
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Dense bodies are analogous to z-lines Places where the thin filaments attach and gives them something to attach to Sliding filament of contraction Like skeletal muscles Cross bridge cycling between actin and myosin Uses Ca to control cross bridge activity Organization is different and the mechanism of excitation is different Structure – Differences in SM No sarcomeres Lack the neat hexagonal arrangement of actin and myosin Actin to myosin ratio in SM is much larger than in skeletal No T-tubule system Poorly developed SR Needs extracellular source of Ca for stimulation No troponin in smooth muscle There is no TROP complex No blocking of active sites Therefore TROP is NOT a mechanism for regulation Not a switch  Cross bridge cycling is controlled by a Ca regulated enzyme that phosphorylates a light  chain on myosin Pnly the phosphorylated form of myosin can bind to actin and engage in cross bridge  cycling
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In skeletal muscle you had to have ATP bound to myosin in order to CB, this is not the  case is SM Thin filaments attached to dense bodies There are also cytoskeletal elements Mechanical mechanism – if you shorten an interval between dense bodies, they will  shorten  Without cytoskeletal elements they would have no innate structure and not really  contract, just be a blob ATPase is cycling a lot slower is skeletal muscle than in skeletal muscle This is demonstrated as skeletal muscle myosin activity is generally 50-100 times that of  typical smooth muscle Types of SM
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