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A skinny, 22 year-old male visits the local clinic complaining of severe…

- - - - Extend the entire length of the A band
      - Connected in the middle of the sarcomere at the M line
      - Each thick filament consists of many myosin molecules whose heads protrude at opposite ends of the filament
    - - Extend across the I band and partway into the A band
      - The Z disc anchors the thin filament
      - Consists of two strands of actin subunits twisted into a helix plus two types of regulatory proteins (troponin and tropomyosin)
    - - The contractile unit, composed of myofilaments made up of contractile proteins (Actin and Myosin)
      - Region of a myofibril between two Z discs
      - The smallest contractile unit of a muscle fiber
    - - Rodlike contractile elements that occupy most of the muscle cell volume
      - Composed of sarcomeres arranged end to end, they appear banded, and bands of adjacent myofibrils are aligned
      - Made up of a chain of sarcomeres linked end to end
      - Has striations. Dark and light bands are evident along the length of each myofibril
      - A dark A band and light I band are perfectly aligned, giving the cell its striated appearance
  - - - An elongated multinucleate cell
      - Has a banded (striated) appearance
      - Surrounded by endomysium
      - Made up of many myofibrils
  - - - A portion of the muscle
      - A discrete bundle of muscle cells
      - Segregated from the rest of the muscle by a connective tissue heath
      - Surrounded by perimysium
  - - - Consists of hundreds to thousands of muscle cells
      - Consists of connective tissue wrappings, blood vessels, and nerve fibers
      - Covered externally by the epimysium
- - - - Transmission of the action potential along the T tubules of the triads causes the voltage-sensitive tubule proteins to change shape
      - This shape change opens the Ca2+ release channels in the terminal cisterns of the sarcoplasmic reticulum, allowing Ca2+ to flow into the cytosol
    - - When Ca2+ binds, troponin changes shape, exposing myosin-binding sites on the thin filaments
    - - Myosin binding to actin forms cross bridges and contraction begins
- - - - Direct phosphorylation
        
        Coupled reation of creatine phosphate (CP) and ADP
        
        Energy source: CP
        
        Oxygen use: None
        
        Products: 1 ATP per CP, creatine
        
        Duration of energy provided: 15 seconds
      - Anaerobic Pathway
        
        Glycolysis and lactic aced formation
        
        Energy source: glucose
        
        Oxygen use: None
        
        Products: 2 ATP per glucose, lactic acid
        
        Duration of energy provided: 30-40 seconds, or slightly more
      - Aerobic Pathway
        
        Aerobic respiration
        
        Energy source: glucose; pyruvic acid; free fatty acids from adipose tissue; amino acids from protein catabolism
        
        Oxygen use: Required
        
        Products: 32 ATP per glucose, CO2, H2O
        
        Duration of energy provided: Hours