MUSCLE CONTRACTION

• MYOSIN= binds to actin and pulls it
• flexors= biceps
• extensors= triceps
• agonist= muscle that contracts, prime mover
• DURING CONTRAXTION WHAT HAPPENS TO THE:
• during contraction what happens to the A BAND?

  unchanged as only mysosin present
• during contraction what happens to the I BAND

  Shortens as myosin moves in so decreases actin length
• during contraction what happens to the H ZONE

  shortens as actin moves in
• during contraction what happens to the Z LINES

  Move closer
• what is the A band

  myosin
• what is the I band

  actin
• what is the Z line

  joins sarcomeres
• SLIDING FILAMENT THEORY

  • myosin and actin filaments slide over each other to make sarcomeres contract
  • the myofilaments themselves DONT CONTRACT
  • sarcomeres return to original length as muscle contracts
• STAGE OF MUSCLE CONTRACTION

  • Ca2+ ions diffuse into myofibrils from sarcoplasmic reticulum and bind to troponin causing tropomyosin to reveal myosin binding sites on actin
  • myosin heads attach to sites
  • hydrolysis of ATP on myosin head causes power stroke so myosin head bends pulling actin molecules and releasing ADP
  • ATP then attaches to myosin head causing myosin to detach from actin sites
  • atp then hydrolysed back to ADP by ATPase releasing energy which resets myosin and sets head back to original position
• TROPONIN= Binds to calcium ions to rel tropomyosin
• TROPOMYOSIN= Blocks myosin binding sites but moves away in ca 2+ influx
• MYOSIN= Binds to actin and pulls it
• atpase is activated by ca2+ ions
• muscles move in antagonistic pairs
• USES OF ATP IN MUSCLE CONTRACTION

  • Rel. myosin from actin binding site causing myosin head to move
  • active transport of ca2+ ions back to SR
  • Attatches to myosin head allowing head to attatch/detach at certain binding sites
• Methods of generating ATP

  • phosphocreatine - hydrolysed to provide phosphate to phosphorylate ADP
  • anaerobic respiration
  • aerobic respiration
• SLOW TWITCH MUSCLES

  • Contract slowly
  • used for posture
  • endurance activities
  • don't fatigue easily
  • energy rel slowly via aerobic respiration
  • rich in myoglobin so red colour
• myoglobin stores oxygen
• FAST TWITCH MUSCLES

  • Contract quickly
  • used for rapid movement
  • short bursts of speed eg.sprinting
  • fatigue quickly
  • energy rel via anaerobic respiration using glycogen
  • not many mitrochondria
  • white as low levels of myoglobin - can't store much o2