Structure of Skeletal Muscle

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Structure of Skeletal Muscle

• Presentation by Angela Holloman

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Introduction

• All activities that involve movement depend on
  muscles
• 650 muscles in the human body
• Various purposes for muscles for
• Locomotion
• Upright posture
• Balancing on two legs
• Support of internal organs
• Controlling valves and body openings
• Production of heat
• Movement of materials along internal tubes
• Three types of muscles in the human body
• Skeletal
• Cardiac
• Smooth

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Skeletal Muscle

• Skeletal muscles are muscles which are attached
  to the skeleton.
• 40 of human body mass
• Skeletal muscles are mainly responsible for
  locomotion, and voluntary contraction and
  relaxation.

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Structure of Skeletal muscles

• Skeletal muscles are composed of clusters of
  muscle cells.
• Muscle fibers
• Myofibers
• Myocytes
• A muscle consists of packages of muscle cells
  called fascicles
• A muscle cell is long and spindle shaped

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Structure of Skeletal muscles

• Cell structure
• Muscles cells contain many nuclei
• The plasma membrane? sarcolemma
• The cytoplasm? sarcoplasm
• Length
• ranges from 0.1cm to more the 30cm in length
• Diameter
• ranges from 0.001cm to 0.01cm in diameter
• Myofibrils?
• elongated protein molecules
• aligned in parallel arrangements
• extend the full length of the cell.

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Structure of Skeletal muscles

• The myofibril consists of protein chains called
  myofilaments
• Myofilaments have a symmetrical, alternating
  pattern of thick and thin elements.

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Skeletal Muscle Myosin

• Thick myofilament
• consists of a large number of bundled myosin
  molecules aligned in overlapping arrays.
• hexameric proteins with two identical heavy
  chains and two pairs of different light chains.
• regulatory light chain (RLC)
• essential light chain (ELC)

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Skeletal Muscle Actin

• The thin myofilament (F-actin, filamentous actin)
  
• made up of two helically intertwined chains of
  G-actin (globular actin) units.
• Other proteins that bind to the actin molecules
• Tropomyosin
• The Troponin complex? made up of three members

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Contraction of Skeletal Muscle

• The thick and thin filaments, along with their
  associated myofibril proteins, are responsible
  for muscle contraction.
• How does muscle contraction work?
• Influx of calcium ions in the cell
• as a result of nerve impulses
• troponin complex pulls tropomyosin molecules away
  from the G-actin subunits
• Exposure of the myosin binding sites.
• The heads of the myosin molecules can bind to the
  actin subunits, forming cross bridges.
• active site in each myosin head disrupts the
  high-energy bond of ATP molecules
• release of energy moves the myosin head towards
  the F- actin,
• when contact is made with the actin subunits, the
  F-actin is pulled along, causing the myofilament
  to contract.
• The coordinated contraction of all the
  myofilaments of all the muscle cells of a muscle,
  causes the entire muscle to contract.

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Relaxation of Skeletal Muscle

• Calcium ions are carried away from the
  myofilaments
• Myosin- actin linkages loosen
• The troponin complex and tropomyosin bind to the
  myosin binding sites on the F-actin subunits,
• Myosin and F- actin myofilaments return to their
  original positions

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References

• Pasternak, Jack J. Human Molecular Genetics
  Mechanisms of Inherited Diseases. Hoboken, New
  Jersey John Wilkey Sons Inc., 2005.
• http//www.lau-verlag.de/anatom/muscleb.jpg.
  March, 20, 2006