unit 5 bio

• Musculoskeletal system


  Support system of animals
• Functions of musculoskeletal system

  • Carrying body weight
  • Withstanding environmental factors
  • Generating forces from movement
• Tension


  When body parts are pulled apart
• Compression


  When body parts are pushed together
• Shear


  When body parts slide over each other
• Components of musculoskeletal system

  • Bones
  • Ligaments
  • Tendons
  • Joints

  
• Bones


  • Microscopic structure: Osteocytes embedded in matrix of collagen fibres and calcium salts
  • Macroscopic structure: Hard vascular tissue
• Skeleton


  • Axial skeleton: Skull, ribcage, vertebral column
  • Appendicular skeleton: Limbs and limb girdles
• Ligaments


  • Structure: Collagen fibres with minimal elastic fibres
  • Functions: Support bone position, allow controlled movement, stabilise joint structure

  
• Tendons


  • Structure: Collagen fibres without elastic fibres
  • Function: Pull distal bones towards proximal bones when muscle contracts
• Joints


  • Synovial joints: Ball and socket, hinge
  • Non-synovial joints: Fixed immobile, intervertebral discs
• Synovial joints


  • Ball and socket: 360 degree movement in 3 planes
  • Hinge: 180 degree movement in 1 plane
• Collagen fibers


  Fibers that provide structure
• Elastic fibers


  Fibers that allow for a range of controlled movement
• Ligaments


  • Support bone position
  • Allow for a range of controlled movement
  • Stabilise joint structure

  
• Cartilage


  Hard avascular tissue composed of chondrocytes embedded in a matrix of collagen fibers

  
• Tendons


  Structures holding muscles to bones
• Tendons


  • Composed of collagen fibers without elastic fibers
  • When a muscle contracts, its tendons pull the distal bones towards the proximal bones
• Joints


  The meeting point of 2 or more bones
• Types of joints


  • Synovial joints
  • Non-synovial joints
• Synovial joints


  • Ball & socket joints (shoulder, hip) allow 360 degree movement in 3 planes
  • Hinge joints (knee, elbow) allow 180 degree movement in 1 plane
• Non-synovial joints


  • Fixed immobile (skull, sacroiliac)
  • Intervertebral discs (cartilaginous)
• Tendons have to be inelastic so that the force generated from muscle contraction can act completely pulling bones
• A torn ligament is replaced by autogenous tendon graft
• Advantages of autogenous tendon graft


  • It's possible to remove part of a tendon, but not part of a ligament
  • No foreign antigens and no risk of tissue rejection
• Disadvantages of autogenous tendon graft

  • The tendon is inelastic, so it takes a long period of physiotherapy to slightly stretch the tendon
  • Relatively slow healing, as different types of tissues are used
• Muscle contraction


  When a muscle contracts it shortens, so its tendons pull the distal bone towards the proximal bone
• Antagonistic muscles


  • Muscles with opposing actions
  • When a muscle contracts, its antagonistic pair relaxes
  • A muscle can shorten only during contraction, but it cannot straighten itself

  
• To lift a weight, the biceps (flexor) contracts and the triceps (extensor) relaxes
• To extend/straighten the arm, the triceps contracts and the biceps relaxes
• To hold a weight steady (90 degree angle), both the biceps and triceps contract
• Muscle fibre


  Muscle cells, which are multinucleated and contain a sarcolemma, sarcoplasm, sarcoplasmic reticulum, and myofibrils

  
• Myofibril


  • Contains thick filaments of myosin protein and thin filaments of actin protein, organised into repeating units called sarcomeres

  
• Muscle contraction


  1. Actin filaments slide over myosin filaments

  2. Z lines get closer

  3. H zone almost disappears

  4. A band does not change

  
• Mechanism of muscle contraction

  The myosin head binds to a complementary site on the actin filament, then tilts to push the actin filament, then detaches and reattaches to the next site, in a rowing motion

  
• Role of calcium ions


  • During relaxation, the myosin binding sites on actin are blocked by tropomyosin
  • Calcium ions released from the sarcoplasmic reticulum activate troponin, which removes tropomyosin and exposes the binding sites
  • For relaxation, calcium ions are actively pumped back into the sarcoplasmic reticulum

  
• Role of ATP


  • Provides energy for the detachment and reattachment of the myosin head
  • Provides energy for the active pumping of calcium ions back into the sarcoplasmic reticulum during relaxation

  
• Sliding filament theory


  1. ATP binds to the myosin head

  2. ATPase breaks down ATP to ADP and phosphate, providing energy for the head to bind to actin

  3. Phosphate release causes the head to tilt, sliding actin over myosin

  4. ADP is then released, allowing the head to detach and straighten, ready to bind to the next site
• Effect of regular exercise on muscles

  • Leads to hypertrophy (increase in size) of muscle fibers due to increase in actin and myosin filaments, but no increase in number of cells

  
• Hemoglobin


  Oxygen transporting protein found in red blood cells