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Sliding Filament Model of Muscle Contraction
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Sliding Filament Model of Muscle Contraction

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  • 1. Anatomy and Physiology Sliding Filament Model
  • 2. Excitation-Contraction Coupling Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.• Muscle impulses cause SR to Tropomyosin Troponin Thin filamentrelease calcium ions into cytosol ADP P + ADP P + Actin monomers• Calcium binds to troponin to Thick filament 1 Relaxed muscle Muscle contraction Muscle relaxationchange its shape Ca+2 Ca+2 Release of Ca from sarcoplasmic +2 Active transport of Ca+2 into sarcoplasmic reticulum exposes binding sites on actin: reticulum, which requires ATP, makes• The position of tropomyosin is Ca+2 binds to troponin myosin binding sites unavailable. ATP Tropomyosin pulled asidealtered Binding sites on actin exposed• Binding sites on actin are now Ca+2 ADP + P Ca+2 ADP P + Ca+2exposed 2 Exposed binding sites on actin molecules allow the muscle contraction cycle to occur• Actin and myosin molecules bindvia myosin cross-bridges ADP P + ADP + P Contraction cycle ADP + P ADP + P 6 ATP splits, which provides 3 Cross-bridges bind actin to power to “cock” the myosin myosin cross-bridges ADP ADP ATP ATP ATP P P ATP ADP +P 5 New ATP binds to myosin, releasing linkages 4 Cross-bridges pull thin filament (power stroke), ADP and P released from myosin 2
  • 3. The Sliding Filament Model of Muscle Contraction Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.• When sarcromeres Sarcomereshorten, thick and thin Z line A band Z linefilaments slide past oneanother• H zones and I bandsnarrow 1 Relaxed Thin Thick filaments filaments• Z lines move closertogether 2 Contracting 3 3 Fully contracted (a)
  • 4. Cross Bridge Cycling• Myosin cross-bridge attachesto actin binding site Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.• Myosin cross-bridge pulls Tropomyosin Troponin Thin filament Actin monomersthin filament ADP P + ADP P + Thick filament 1 Relaxed muscle• ADP and phosphate Muscle contraction Release of Ca from sarcoplasmic +2 Ca+2 Ca+2 Muscle relaxation Active transport of Ca+2 into sarcoplasmicreleased from myosin reticulum exposes binding sites on actin: Ca+2 binds to troponin reticulum, which requires ATP, makes myosin binding sites unavailable. ATP Tropomyosin pulled aside• New ATP binds to myosin Binding sites on actin exposed Ca+2 Ca+2 Ca+2 ADP + P ADP P + 2 Exposed binding sites on actin molecules• Linkage between actin and allow the muscle contraction cycle to occurmyosin cross-bridge break ADP P + ADP + P Contraction cycle ADP + P ADP + P 6 ATP splits, which provides 3 Cross-bridges bind actin to power to “cock” the myosin myosin• ATP splits cross-bridges• Myosin cross-bridge goes back ATP ATP ATP P ADP P ADP ATP ADP +Pto original position 5 New ATP binds to myosin, releasing linkages 4 Cross-bridges pull thin filament (power stroke), ADP and P released from myosin 4
  • 5. Animation: The Cross-Bridge Cycle Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 5
  • 6. Animation: Breakdown of ATP and Cross-Bridge Movement Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 6
  • 7. Relaxation• Acetylcholinesterase – rapidly decomposes Ach remaining inthe synapse• Muscle impulse stops• Stimulus to sarcolemma and muscle fiber membrane ceases• Calcium moves back into sarcoplasmic reticulum (SR)• Myosin and actin binding prevented• Muscle fiber relaxes 7
  • 8. References• Shier, D., Butler, J., and Lewis, R. 2010. Hole’s Human Anatomy & Physiology, New York. 8