skeletal muscles

• what are myofibrils made up of

  proteins: myosin & actin that form a sarcomere.
• myosin:

  thick filaments

  dark bands: A bands

  H zone only consists of myosin
• actin

  thin filaments

  light bands: I bands
• sarcomere structure:

  • ends of sarcomere: Z line
  • middle of sarcomere: M line
  • around the M line: H zone
• sliding filament theory:

  once action potential reaches the muscle, causes Ca 2+ to be released from sarcoplasmic reticulum 

  Ca 2+ binds to a protein attached to tropomyosin causing it to move and exposes binding sites 

  myosin head attaches to exposed binding sites (actin filament) and it forms actin-myosin cross bridge

  hydrolysis of ATP causes myosin head to bend - pulling actin molecules

  attaching a new ATP to myosin head for it to detach from actin sites
• role of phosphocreatine:

  chemical stored in muscles used to regenerate ATP from ADP by providing phosphate
• slow twitch muscle fibres

  contracts slowly

  work for long periods of time without fatigue

  good for endurance activities

  used for posture

  large store of myoglobin & mitochondria & blood vessels

  energy released slowly via aerobic respiration
• fast twitch muscle fibres

  contract quickly

  used for fast movements

  good for intense activities

  found in arms,legs

  few mitochondria + blood vessels

  energy released quickly via anaerobic respiration
• gross structure of skeletal muscle