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Motor mechanisms

Motor mechanisms. Keywords (reading p. 1080-1086). Bundle, fiber, myofibril, sarcomere Z-line, thick filament, thin filament Actin, myosin, sliding filament model Molecular basis for filament movement Troponin, tropomyosin Sarcoplasmic reticulum Integration of synaptic signals

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Motor mechanisms

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  1. Motor mechanisms

  2. Keywords (reading p. 1080-1086) • Bundle, fiber, myofibril, sarcomere • Z-line, thick filament, thin filament • Actin, myosin, sliding filament model • Molecular basis for filament movement • Troponin, tropomyosin • Sarcoplasmic reticulum • Integration of synaptic signals • neurotransmitters

  3. Motor mechanisms • Create movement • Can be cilia, flagella, contractile proteins, muscles • Will focus on skeletal muscle • Muscle of vertebrates that is under voluntary control

  4. Structure of skeletal muscle • Bundle • Fiber • Myofibril • sarcomere Part of Campbell 6th ed p. 1081

  5. Features of muscle cells • # of nuclei- multinucleate; formed by fusion of embryonic cells • length - this results in very long cells Part of Campbell 6th ed p. 1081

  6. Sarcomere • Structure gives muscle a striated appearance • Z line, thick filaments (myosin), thin filaments (actin) Part of Campbell 6th ed p. 1081

  7. Part of Campbell 6th ed p. 1081

  8. Part of Campbell 6th ed p. 1081 Sliding-filament model of muscle contraction

  9. Part of Campbell 6th ed p. 1081 Thick and thin filaments slide past each other

  10. At maximal contraction, there is no space at end of thick filament,thin filaments overlap Part of Campbell 6th ed p. 1081

  11. http://www.youtube.com/watch?v=InIha7bCTjM&feature=related Molecular basis for movement of filaments against each other Part of Campbell 6th ed p. 1082

  12. ATP bound, head retracted and unattached Part of Campbell 6th ed p. 1082

  13. Hydrolysis of ATP cocks head Part of Campbell 6th ed p. 1082

  14. Myosin head attaches to actin filament Part of Campbell 6th ed p. 1082

  15. Release of ADP + Pi causes a further conformational change pushing against the actin filament Part of Campbell 6th ed p. 1082

  16. Binding of ATP to myosin head causes dissociation from actin filament Part of Campbell 6th ed p. 1082

  17. Cycle repeats and sarcomere shortens Part of Campbell 6th ed p. 1082

  18. Control of muscle contraction by Ca++ • Tropomyosin- blocks the myosin binding sites on the actin filament when muscle is at rest • Troponin complex-binds calcium and controls the position of tropomyosin

  19. At rest, myosin cannot bind because sites are covered by tropomyosin http://www.youtube.com/watch?v=WRxsOMenNQM Part of Campbell 6th ed p. 1083

  20. During muscle contraction Ca++ levels rise. Ca++ binds to troponin which then pulls tropomyosin way from the binding sites Part of Campbell 6th ed p. 1083

  21. What triggers the Ca++ rise that induces muscle contraction?

  22. [Ca++] regulated by the sarcoplasmic reticulum Campbell 6th ed p. 1083

  23. Structure of the sarcoplasmic reticulum • T tubules - are a network of the fiber plasma membrane that goes deep into the muscle fiber. • This allows transmission of the action potential into the fiber

  24. Sequence of events leading to muscle contraction • Motor neuron releases acetylcholine • Depolarization of the muscle fiber membrane results in action potentials • Action potentials trigger release of Ca++ from the sarcoplasmic reticulum • Increased Ca++ allows actin and myosin to slide against each other

  25. Characteristics of other muscle types: • Cardiac muscle - found only in the heart, striated, gap junctions allow direct electrical signaling between cells • Smooth muscle - involuntary muscle, meshwork of actin and myosin, can contract more (greater shortening), but with less tension.

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