Skeletal muscle

• Whats the difference between voluntary and involuntary muscles

  Voluntary muscles like skeletal muscles are striated and contain actin and myosin

  (smooth muscle also contain them but in very little amounts)
• Involuntary muscles include cardiac muscle (heart) and smooth muscle
• Thick filaments are myosin
• Thin filaments are actin
• Sarcomeres are repeating units within muscle fibres that contract to produce movement.
• Label

  Z line - appears dark in the middle of the I band but just connects sarcomeres

  M line - the middle of the myosin filaments where the thin filaments head towards during contraction

  A band - the whole region of the thick filament and remains unchanged

  H zone - region of non overlap of the myosin with actin and gets smaller during smaller during muscle contraction

  A) Thick

  B) Thin

  C) M

  D) z

  E) z

  F) I

  G) I

  H) A

  I) H

  
• Sliding filament mechanism


  1. Ca2+ ions cause tropomyosin to move and expose actin binding sites
  2. Myosin head attaches to binding site forming cross bridges
  3. ADP and Pi are released causing a power stroke
  4. ATP binds to myosin head to detach it from actin
  5. Myosin head hydrolyses ATP and returns to starting position
  6. REPEAT
• during muscle contraction (in regards to lines, bands and zones)

  The Z line approaches the M line

  The H zone and I band decrease
• Muscle relaxation is caused by Ca2+ being pumped back into sarcoplasmic reticulum so there aren't enough free calcium ions to activate troponin which means tropomyosin covers up the active sites on actin again preventing cross bridges forming between them
• The cholinergenic synapse

  1. nerve impulse arrives
  2. voltage gated calcium channels open
  3. Ca2+ ions enter and cause vesicles to fuse with the presynaptic membrane and deposit ACH
  4. ACH diffuses across the synapse and binds to receptors on sodium channels and opens them
  5. influx of Na+ ions in post synaptic neurone causing depolarisation
  6. In a neuromusclar junction the muscle would just contract