skeletal muscle

• skeletal muscle is usually connect to the skeleton by tendons
• skeletal muscle function

  • movement
  • maintain posture
  • support soft tissue
  • control openings and exits
  • maintain body temperature
  • nutrient reserve
• organisation of skeletal muscle

  labels

  A) blood vessel

  B) perimysium

  C) epimysium

  D) fascicle

  E) endomysium

  F) tendon

  G) muscle fibre

  
• muscle fibre structure

  • myoblast cells fused
  • multinucleate (under sarcolemma)
  • long (entire length of skeletal muscle)
  • striated (aligned sarcomeres)
• skeletal muscle fibre

  labels

  A) sarcolemma

  B) nuclei

  C) myofibrils

  D) mitochondria

  
• myofibrils are comprised of many myofilaments arranged into 


  sarcomeres
• muscle fibres contain many myofibrils
• structure of muscle fibre

  labels

  A) myofibril

  B) sarcomere

  C) I band

  D) A band

  E) I band

  
• myofilaments are composed of thick and thin filaments
• thin filament is 


  actin
• thick filament is 


  myosin
• T tubules function 


  transfer action potentials to myofibrils
• myofibrils are surrounded by sarcoplasmic reticulum which stores

  calcium ions
• M line function

  attaches thick filaments together
• A band contains 


  myosin and actin
• A band is a dark band
• I band contains 


  only actin
• I band is a light band
• H band contains 


  only myosin
• Z line function 


  joins adjacent sarcomeres
• thick filaments interact with thin filaments during contraction, bringing thin filaments towards the

  M line
• lots of myosin molecules wound together makes a

  thick filament
• titin function 


  prevents over-extension of sarcomere
• thin filament is made of actin and has regulatory proteins attached
• what are the regulatory proteins attached to the thin filaments

  troponin and tropomyosin
• myosin binding site on actin is covered by _ when relaxed

  tropomyosin
• calcium binds to troponin which causes tropomyosin to uncover the myosin binding site on actin
• sliding filament theory mechanism

  1. action potential arrives causing release of calcium
  2. calcium ions bind to troponin, so tropomyosin move and uncovers myosin binding site on actin
  3. cross bridge formation (myosin and actin bind)
  4. power stroke (stored energy in myosin head is released and myosin head pivots)
  5. cross bridge breaks when ATP binds myosin head
  6. myosin reactivated (myosin head splits ATP into ADP and Pi, myosin head is re-cocked for another cycle)
• contraction cycle repeats if calcium is still present
• combination of many myosin heads causes actin filament to slide past myosin filaments
• regulating muscle contraction

  • muscle fibres innervated by motor neuron (ending in neuromuscular junction)
  • activation of motor neuron
  • action potential then travels to muscle fibre
  • release of acetylcholine from synapse
  • ACH binds to receptor on sarcolemma
  • depolarisation of muscle fibre
  • T-tubule transfer action potential to sarcoplasmic reticulum
  • calcium released from sarcoplasmic reticulum
  • calcium binds to troponin, causing conformational change of tropomyosin, exposing myosin binding site
  • contraction occurs
• contraction ends by

  • Ach broken down in synaptic cleft
  • calcium stops being released from sarcoplasmic reticulum
  • calcium ions pumped back into sarcoplasmic reticulum
  • calcium detaches from troponin, tropomyosin recovers myosin binding site