Muscle tissue and muscle contraction

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CLIL SCIENCE

• Muscle tissue and muscle contraction
• Rosalie Crawford - Veronica RevelFondazione
  Liceo Linguistico Courmayeur

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How does it happen?? How do our muscles work??
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Skeletal, cardiac and smooth muscle
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Skeletal muscle fibre
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The structure of skeletal muscle

• The sarcomere is composed of two types of
  filaments running parallel to one another. The
  thicker filaments are composed of the protein
  myosin while the thinner ones are primarily actin.

• A group of myofibrils (from myo, the prefix for
  muscle), each of which is surrounded by the
  specialized endoplasmic reticulum of muscle
  cells, the sarcoplasmic reticulum.
• The sacs of the sarcoplasmic reticulum contain
  calcium ions (Ca2) , which, when released,
  trigger muscle contraction.
• Myofibrils are composed of units called
  sarcomeres, which have two types of filaments
  running parallel.

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What causes a muscle contraction?

• Muscle contractions occur as the sarcomeres
  present in muscle fibers shorten. When muscle
  fibres are triggered by neuromuscular junctions,
  a process begins in which thick and thin
  filaments overlap causing the sarcomeres to
  shorten over a brief period of time. The thick
  filaments are composed of about 200 mysosin
  fibres that look similar to golf clubs. Along the
  long filament, the myosin proteins line up in
  opposite directions with their heads protruding
  out from the filament. The thin filaments,
  composed of actin, tropomyosin, and troponin,
  form a spiral helix with myosin binding sites on
  the actin.

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The cycle of muscle contraction
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Muscle contraction

• When a muscle contraction is triggered,
• 1) calcium ions and energy-supplying ADP cause
  rearrangement of the thin filaments,
• 2) the myosin heads bind to the actin,
• 3) the myosin heads pull the thin filaments
  towards the center of the sarcomere.
• Once contraction is complete, ATP binds to
  myosin, the myosin-actin bond is broken, and the
  myosin head re-cocks to the starting position
  until the cycle repeats. This cycle occurs
  simultaneously in many muscle fibers present in
  the entire muscle tissue causing contractions in
  the muscles of your eye, to the movement of your
  arms and legs.

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Molecular mechanism of muscular contraction
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Isometric isotonic contractions

• Skeletal muscles undergo two types of
  contractions isometric and isotonic. Because
  isometric contractions occur when the muscle does
  not shorten, as when pushing against a wall, no
  work is done and no power is produced. In
  isometric contractions, myofibrils slide over
  each other causing the sarcomeres to shorten and
  external work is performed.