Muscles

• Muscles are antagonistic pairs against the skeleton, controlled by automatic or conscious control
• Myofibrils are fused cells sharing nuclei and cytoplasm (sarcoplasm), with a high concentration of mitochondria
• Sarcomeres are the thin, flexible structures made of actin and myosin
• A-Bands are the length of myosin fibres, remaining a constant length
• H-Zone is the length of myosin where no actin is overlapping, length changes size, decreasing
• I-Bands are the lengths of actin only, changing lengths when contracting
• Z-Lines are the start and end lines of the sarcomere, becoming closer together during contraction
• Sliding Filament Theory:

  • Action potential stimulates contraction via Ca2+ ions to influx in
  • Ca2+ ions bind to tropomyosin protein, moving them to uncover binding sites on actin
  • Myosin + ADP attaches to binding sites, forming a cross-bridge
  • The cross-bridge creates tension, causing a sliding action of actin (power stroke), this releases ADP + Pi
  • ATP then binds to myosin, changing the shape slightly, detaching from the binding site
  • ATPase is activated by Ca2+ ions, hydrolysing ATP, causing myosin to return to its original position
• Phosphocreatine is stored in the muscles, providing phosphate to regenerate ATP from ADP