PHYSIO MUSCLE CONTRACTION LEC

• Movement is an impo ant characteristic of animals
• Most animal movement depends on a single fundamental mechanism: contractile proteins, which can change their form to allow relaxation and contraction
• The most impo ant protein contractile system is the actomyosin system, composed of two proteins, actin and myosin
• Pseudopodia ("false feet) of the amoeba

  • Cell migration involves: 1) Protruding of pseudopodia driven by the aggregation and activation of the adhesion complex, 2) Formation of new adhesions driven by actin laments, 3) Development of traction, 4) Release of old adhesions
• Structure of a eukaryotic cilium

  • 9+2 arrangement of microtubules and microtubule-associated proteins (MAPs), central pair of microtubules end near the level of the cell suace
• Structure of a eukaryotic flagellum

  • Similar internal structure to cilia, main dierence is in beating pattern - flagella beat symmetrically with snakelike waves, cilia beat asymmetrically with a fast power stroke and slow recove£
• Functions of muscular tissue

  • Producing body movements
  • Stabilizing body positions
  • Storing and moving substances within the body
  • Generating heat
• Types of inve ebrate muscle

  • Smooth, striated, and oblique striated muscles
• Specialized adductor muscles of molluscs

  • One type is striated muscle that can contract rapidly, enabling the bivalve to snap shut its valves when disturbed, the other type is smooth muscle capable of slow, long-lasting contractions
• Insect ight muscles

  • Brillar muscle that contracts at frequencies greater than 1000 beats per second, has ve£ limited extensibility
• Tropomyosin

  A protein that winds around the chains of the actin lament and covers the myosin-binding sites to prevent actin from binding to myosin, binds to troponin to form a troponin-tropomyosin complex
• Troponin-tropomyosin complex

  Prevents the myosin "heads" from binding to the active sites on the actin microlaments, troponin has a binding site for Ca++ ions
• The Cross-bridge Cycle

  Tropomyosin has to expose the myosin-binding site on an actin lament to allow cross-bridge formation, 2) Ca++ bind to troponin so that tropomyosin can slide away from the binding sites on the actin strands allowing the myosin heads to bind, 3) The thin laments are then pulled by the myosin heads to slide past the thick laments toward the center of the sarcomere
• Sources of ATP

  • Creatine phosphate metabolism
  • Anaerobic glycolysis
  • Fermentation and aerobic respiration
• Creatine phosphate metabolism

  Creatine phosphate acts as an energy rese¡e that can be used to quickly create more ATP, can only provide approximately 15 seconds wo h of energy
• As contraction sta s

  ATP stored in resting muscle is used up in seconds, more ATP is generated from creatine phosphate for about 15 seconds
• Anaerobic glycolysis

  Produces 2 ATP and 2 molecules of pyruvic acid, if oxygen is not available pyruvic acid is conve ed to lactic acid which may contribute to muscle fatigue
• Aerobic respiration

  Breakdown of glucose in the presence of oxygen to produce carbon dioxide, water, and ATP, provides approximately 95 percent of the ATP required for resting or moderately active muscles