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Muscle Contractions

This detailed overview explores the sliding filament mechanism of muscle contraction, highlighting how myosin and actin filaments slide over each other to change muscle length. Essential processes such as the role of calcium ions, the neuromuscular junction, and the interactions between motor neurons and muscle fibers are discussed. We outline the sequential steps of contraction from action potential generation to muscle relaxation, detailing the importance of ATP and the cycling of myosin heads. This resource includes links to animations for a visual understanding.

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Muscle Contractions

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  1. Figure 39-4 Muscle Contractions

  2. Sliding Filament Mechanism • _________ and_______filaments slide over each other______________the muscle length • Always requires ________ ions and ___

  3. Actin • Double chain of ______ proteins • Makes up ____ filament • Attached to end walls of sarcomeres called _____ • Makes up __ band of sarcomere • Has ______ binding site which is blocked by ____________ and ____________ in relaxed muscle

  4. Myosin • Makes up _______ filament • Has myosin ________ which bind to _______ • Make up ___ bands in a sarcomere

  5. Neuromuscular Junction • “Joining” of motor ______ and ___________ • _______________-motor neurons release _________________ that diffuse across synapse to receptors on muscle fiber membrane • Always ______________ • Motor unit-_______branched motor ________ synapsing with ______ muscle _______

  6. 11 Steps of a Muscle Contraction • An __________________travels down a motor neuron • The skeletal muscle _________ is activated at the ____________________ junction • An _____________________travels down the muscle __________________________ • The action potential enters _____________ • An action potential stimulates the ____________________________________

  7. 11 Steps of a Muscle Contraction Cont. 6. ______________________are released into the muscle cell ____________________ 7. _____________ ions bind to _____________ 8. ___________________ exposes ___________ binding sites on _________ 9. Myosin _______ bind to ________ 10. Myosin heads __________ 11. _______ filaments are pulled toward sarcomere center, and muscle fiber ________

  8. Muscle Relaxation • When action potential is over, ________ goes back to _______________________________ • Calcium is removed from _____________ • Troponin and tropomyosin ________ myosin binding sites • Muscle ____________

  9. 1 - Calcium released from sarcoplasmic reticulum 2  - Myosin head energized via myosin-ATPase activity which converts the bound ATP to ADP + Pi 3 - Calcium binds to troponin 4 - Tropomyosin translocates to uncover the cross-bridge binding sites 5 - The energized myosin binding sites approach the binding sites 6 - The first myosin head binds to actin 7 - The bound myosin head releases ADP + Pi, flips and the muscle shortens 8 - The second myosin head binds to actin 9 - The first myosin head binds ATP to allow the actin and myosin to unbind 10 - The second myosin head releases its ADP + Pi, flips & the muscle shortens further 11 - The second myosin head binds to ATP to allow the actin and myosin to unbind 12 - The second myosin head unbinds from the actin, flips back and is ready for the next cycle 13 - The cross-bridge cycle is terminated by the loss of calcium from the troponin 14 - Tropomyosin translocates to cover the cross-bridge binding sites 15 - The calcium returns to the sarcoplasmic reticulum, the muscle relaxes & returns to the resting state

  10. Contraction Clip • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/animation__sarcomere_contraction.html http://www.youtube.com/watch?v=EdHzKYDxrKc&feature=player_embedded http://www.youtube.com/watch?v=gJ309LfHQ3M&feature=player_embedded

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