Muscle and the Sliding filament theory

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Muscle and the Sliding filament theory
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Skeletal muscle development

• Myoblasts
• one nucleus each
• lacking myofibrils

• Myotubes
• develop myofibrils
• Many nuclei

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Skeletal and Cardiac Muscle

• Both demonstrate striations or stripes when
  seen with a microscope
• These stripes represent the regular arrangement
  of actin and myosin

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• Myosin is a thick protein and looks dark in the
  section
• Actin is a very small protein and looks pale in
  the section.

The dark ovals are the nuclei of the muscle
cells. There may be up to A 100 nuclei per cell
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Sarcomeres

• Functional contractile unit of striated muscle
• 2-3 mm in length
• Striations
• Made up of regular overlapping pattern
• of actin (thin filaments)
• myosin (thick filaments)
• Delineated by Z lines
• Center line is I band

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Very close image of muscle
A band myosin I band actin Z lines where the
actin attaches and the end of a sarcomere
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Muscle contraction

• When muscle contracts,
• all of the actin
• (white in the picture, red in the diagram)
• will slide over
• the myosin
• (black in the picture, green in the diagram).
• The Z discs will come closer
• All of these millions of shortenings in one
  muslce will result in muscle contractions

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Sliding filament mechanism

• Sarcomeres shortened
• Thin filaments slide over thick filament
• Requires ATP
• The cells source of energy
• other proteins and calcium

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Animation of sliding filament

• http//3dotstudio.com/zz.html