Skeletal Muscle Microscopic Anatomy

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Skeletal Muscle Microscopic Anatomy

• Fig. 6.3, pg. 159
• The myofibrils are chains of tiny contractile
  units called sarcomeres, which are aligned end to
  end
• It is the arrangement of even smaller structures
  (myofilaments) within the sarcomere that produce
  a banding pattern

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How Does It Work?
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Skeletal Muscle Banding Pattern

• Alternating light (I band) and dark (A band)
  bands along the length of the perfectly aligned
  myofibrils give the muscle cell as a whole its
  striped appearance.
• The I band has a midline interruption, a darker
  area, called the Z line.
• The dark A band has a lighter central area called
  the H zone

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Two types of Myofilaments

• myosin filaments thick
• actin filaments thin

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Myosin Filaments

• larger thicker filaments
• Extend the entire length of the dark A band
• The midparts of the thick filaments are smooth,
  but their ends are studded with small
  projections, or myosin heads.
• These myosin heads are sometimes called
  crossbridges because they link the thick and thin
  filaments together during contraction

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Actin Filaments

• Anchored to the Z line
• The light I band is an area that includes parts
  of two adjacent sarcomeres and contains only the
  thin filaments
• Although the thin filaments overlap the ends of
  the thick filaments, they do not extend into the
  middle of a relaxed sarcomere, and thus the
  central region (the H zone) looks a bit lighter

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Review so far.

• http//lessons.harveyproject.org/development/muscl
  e/grsphysw.html
• http//lessons.harveyproject.org/development/muscl
  e/swstfast.html