Week 5

Week 5

1. Skeletal Muscle

   • Structure
     • 3 connective layers
       • epimysium - outer
       • perimysium - surrounds fascicle
       • endomysium - inner
     • fibres collect in bundles
     • bundles group together along blood vessels
     • fibre
       • myofibrils
       • sarcoplasm
       • nuclei
       • mitochondria
       • capillary
       • sarcolemma
       • nerve
       • satellite cell
         • satellite cells are found under the basal lamina
         • satellite cells are used for growth and regeneration
     • multinucleated - 1 nucleus every 15 sarcomeres
     • muscle cells fuse together to form 1 cell
     • proliferating myoblasts are made in the body and move to the limbs during gestation
   • Sarcomeres
     • structure
       • I band - thin filament, Z disc
       • A band - thick filament, M line
     • contraction
       • A band width does change
       • I band width decreases
       • thick and thin filaments slide past each other
     • thick filament
       • myosin
         • 3 subunits
           • sub 1 - motor domain, bind to nucleotides, bind to actin, 2 heavy chains
           • sub 2 - 4 light chains, 2 essential, 2 regulatory
           • light meromyosin - coiled coil, alpha helices, converge to form a thick filament
       • each filament contains 294 molecules
       • parallel and anti-parallel packing
       • 14.3nm axial repeat
     • thin filament
       • actin
       • fast growing end - barbed, negative, capping protein
       • slow growing end - pointed, positive
       • anchored to the Z disc
       • cross linked to alpha-actinin
       • tropomoldulin caps the pointed end to stop it growing
   • ATP Cycle
     • ATP binds to myosin
     • ATP is phosphorylated and binds to actin and it moves forward
     • ADP detaches and the cycle starts again
   • Force of Movement
     • depends on number of cross bridges
     • depends on the amount of overlap
     • zero force at overlap
     • all sarcomeres contracting cause the muscle to contract
   • Tropomyosin & Troponin
     • tropomyosin
       • 2 long strands wrap around actin
       • 1 for every actin subunits
       • 3 subunits
         • TnC - binds Ca
         • TnL - inhibitory, binds to TnC, TnT and actin
         • TnT - binds to tropomyosin
       • how it works
         • Ca binds to TnC
         • TnL binds to TnC
         • Myosin binding sites open
         • Enter text here

2. Cardiac & Smooth Muscle

3. Mechanics of Muscle Contraction

4. Muscle Function During Locomotion