Muscle Contraction
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Muscle Contraction






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Muscle Contraction Muscle Contraction Presentation Transcript

  • بسم الله الرحمن الرحيم الحمد لله رب العالمين الذي هدانا لهذا وما كنا لنهتدي لولا أن هدانا الله والصلاة والسلام على أشرف الأنبياء والمرسلين
  • Muscular system
    • Skeletal muscle is made up of hundreds of muscle fibers
      • Fibers consists of threadlike myofibrils
      • Myofibrils composed of smaller myofilaments
      • Striations reflect the overlapping of muscle filaments
  • Skeletal Muscles Structure
    • Muscle are composed of bundles of muscle fibers , which in turn are made of bundles of myofibrils .
    • Muscle fiber:
    • Sarcolemma : the plasma membrane with inward extensions form T tubules.
    • Sarcoplasm: refers to the cytoplasm.
    • Sarcoplasmic reticulum : the ER in muscle.
    • Myofilaments actin and myosin , which are organized into contractile units called
    • Sarcomeres : basic units connected end-to-end by Z- line to form myofibrils.
  • The Myofilaments
    • The thick filaments and the thin filaments. 
    • These two filaments are arranged within the sarcomere in an overlapping manner. 
    • Thin filaments are composed of the protein actin , the helical backbone of thin filament. 
    • Each actin protein contains an active site which interacts with the myosin head. 
    • Two other proteins are present in the thin filaments, tropomyosin and troponin .
    • Thick filaments are composed of a myosin .  The head extends out from the filament forming cross bridges which interact with the thin filaments
  • Sarcomere
      • Contractile unit
      • Actin (thin) filaments
      • Myosin (thick) filaments
  • Steps in muscle contraction
      • Acetylcholine released by a motor neuron combines with receptors on the surface of a muscle fiber
      • Calcium ions released from the sarcoplasmic reticulum
      • Calcium ions bind to troponin in the actin filaments causing the troponin to change shape
      • Troponin pushes tropomyosin away from the active sites on the actin filaments
      • ATP binds to myosin
      • ATP is split, putting the myosin head in a high-energy state
      • Energized myosin heads bind to the exposed active sites on the actin filaments
      • The actin filament is pulled toward the center of the sarcomere
      • Myosin head binds a new ATP
      • Myosin head detaches from the actin
      • Myosin reattaches to new active sites so that the filaments are pulled past one another
      • Muscle continues to shorten
    • Contraction of skeletal muscle is initiated when an action potential traveling down a motor neuron reaches the neuromuscular junction .
    • Motor neuron releases acetylcholine into synaptic cleft, which binds with receptors on muscle fiber.
    • Depolarizes (change in electric charge) the sarcolemma of the muscle fiber.
    • This action potential travels down the inward-projecting  T tubules that reach deep into the muscle fiber.
    • Depolarization of T tubules opens calcium channels in the sarcoplasmic reticulum.
    • Causing the to release of stored calcium ions.
    • Ca 2+ then diffuse into the myofibrils and bind to troponin complex, which change its shape.
    • Pushing tropomyosin away from the active sites on the actin filament .
    • Expose myosin-binding sites , which are capable of interacting with myosin heads, forming cross bridges after ATP breakdown to ADP& P i .
    • A new ATP binds to myosin heads, breaking the cross bridges and myosin detach from actin .
    • Tropomyosin then covers active sites on the actin molecules and relaxation occurs.
    • After contraction, ACH inactivated , the Ca 2+ moves back into the sarcoplasmic reticulum.
  • Muscle contraction
  • Myosin head (H) attaches to actin filament (A), forming a crossbridge.
  • Providing energy for muscle contraction
      • ATP hydrolysis provides the energy to “cock” the myosin
      • Creatine phosphate is used for intermediate energy storage
      • Glycogen is the fuel stored in muscle fibers
  • Antagonistic action of skeletal muscles
      • Agonist muscle contracts
      • Antagonist muscle relaxes
      • Groups of muscles work together
      • Series of separate stimuli timed close together produces a smooth, sustained contraction
  • Muscle action