topic 11.2: Movement

• Musculoskeletal system


  Roles: movement, support, protection
• Bone


  • Rigid nature supports and protects organs
  • Provides structure for muscles to pull and create movement

  
• Antagonistic pairs of muscles in an insect leg

  • Extensor tibiae muscle
  • Flexor tibiae muscle
• Annotation of a diagram of the human elbow

  1. Biceps

  2. Triceps

  3. Humerus

  4. Radius/Ulna

  5. Cartilage

  6. Synovial fluid

  7. Joint capsule

  8. Tendons

  9. Ligaments

  
• Synovial joints


  Allow certain movements but not others
• Skeletal muscles exist in antagonistic pairs
• Skeletal muscle


  • Responsible for voluntary movements
  • Consists of muscular bundles surrounded by connective tissue
  • Fibres contain many myofibrils arranged into repeating sarcomeres

  
• Skeletal muscle fibres


  • Multinucleate
  • Contain specialized endoplasmic reticulum

  
• Drawing labelled diagrams of the structure of a sarcomere

  1. Z lines

  2. Actin filaments

  3. Myosin filaments with heads

  4. Light and dark bands
• Endoplasmic reticulum


  Synthesizes molecules
• Skeletal muscle fibres


  • Multinucleate
  • Contain specialized endoplasmic reticulum

  
• Muscle fibres


  • Contain many myofibrils

  
• Sarcolemma

  Plasma membrane that holds muscle fibre cells together
• Myofibrils


  Basic rod-like contractile units within muscle cells

  
• Myofibrils


  • Grouped together inside muscle cells, which are known as muscle fibres

  
• Myofibril


  • Made up of contractile sarcomeres
• Muscle contraction


  1. Sarcolemma depolarisation and calcium release

  2. Actin and myosin cross-bridge formation

  3. Sliding mechanism of myofilaments

  4. Sarcomere shortening
• Sarcolemma depolarisation


  Nerves stimulate muscle fibre
• Cross-bridge formation


  Calcium ions displace blocking complex on actin filaments, allowing actin to bind to myosin
• Sliding mechanism


  1. ATP binds to myosin head, breaking cross-bridge

  2. ATP hydrolysis causes myosin head to swivel

  3. Swiveled myosin head detaches from ADP and binds to next actin binding site

  4. Myosin head returns to original configuration, moving actin strand
• ATP hydrolysis and cross-bridge formation are necessary for the filaments to slide
• Calcium ions, tropomyosin and troponin


  Control muscle contractions
• The sliding mechanism is an energy-intensive process that requires ATP hydrolysis
• Sarcomere shortening

  I bands become narrower, A bands stay the same (but H zone reduced)
• Electron micrographs can be used to analyse the state of contraction of muscle fibres

  
• Fluorescent calcium ions (aequorin) and dyes have been used to study the rapid movements in muscle contraction
• Ashley and Ridgway (1968) were the first to study the role of calcium ions in coupling nerve impulses and muscle contraction using aequorin
• Fluorescent dyes have been used to visualise and measure the movement of myosin and actin