skeletal muscle structure

• Functions of skeletal/striated muscle tissue:

  • Movement 
  • Protection 
  • Shape 
  • Support 
• Ultrastructure of muscle fibre 

  • Myofibrils - mini fibres inside the muscle fibre - composed of protein
• Actin:

  • Repeating subunits 
  • Thin filament
  • They are dimers, 2 polypeptide chains of actin wound together - increase strength 
  • There are 2 additional proteins tropomyosin (runs through actin fibre - fundamental to muscle contraction) and troponin (sits at regular intervals along actin filament - these are not fibrous proteins - also important in muscle contraction)
• Myosin:

  • Also form dimers - but has 2 distinct groups 
  • Consists of 2 heads and tails (tail region and myosin head region)
  • Many dimers come together to for myosin filament - thicker than actin filament
  • Myosin heads stick out round the exercise - give strength 
• relaxed muscle - Small overlap between actin and myosin when relaxed 
• muscle contracted - Myosin and actin overlap 
• when muscles contract, the A- band stays the same length and the I- band gets shorter, H-zone gets shorter
• A-band = darkest band - contains myosin and actin

  I-band = light band - only contains actin

  H-Zone = dark band - myosin only