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A skinny, 22 year old has severe cramping in calves, thighs, buttocks,…

- - - - Skeletal muscle has a rich blood supply. Contracting fibers use huge amounts of energy and require almost continuous delivery of oxygen and nutrients via arteries
        
        Capillaries flow through muscles and straighten when the muscle stretches and contort when the muscle contracts.
    - - Epimysium - "overcoat" of dense irregular connective tissue that surround the whole muscle.
      - Perimysium and fascicles - within each skeletal muscle , the muscle fibers are grouped into fascicles that resembles bundles of sticks. surrounding each fascicle is a layer of dense irregular connective tissues called perimysium
      - Endomysium - "within the muscle" is a wispy sheath of connective tissue that surrounds each individual muscle fiber. it consist of fine areolar connective tissue.
      - Muscle fiber - an elongated multinucleate cell , branded striated appearance.
      - Myofibril - rodlike contractile elements that occupy most of the muscle cell volume . composed of sarcomeres arranged end to end, appear banded.
      - Sarcomere - is a contractile unit , composed of myofilaments made up of contractile proteins .
      - Myofilament - contractile myofilaments of two types. Thick filaments contain bundled myosin molecules ; thin filaments that contain actin molecules. These provide elastic recoil the tension is released.
  - - - myofibrils are made of a chain of sarcomeres linked end to end. and contain even smaller rodlike structures called myofilaments
        
        striations - repeating series of dark and light bands
        
        dark A bands and I bands are perfectly aligned giving the cell its striated appearance
        
        each A band has a lighter region in its midsections called the H zone. H for Helle "bright"
        
        Each H zone is bisected vertically by a dark line called the M line M for middle formed by molecules of the protein Myomesin
        
        each light I band also has a midline interruption, a darker area called the Z disc
  - - - Concentric - are those in which the muscle shortens and does work, such as picking up a book or kicking a ball
      - Essentric - in which the muscle generates force as it lengthens, are equally important for coordination and purposeful movements.
    - - tension may build up to the muscles peak to the muscles peak tension producing capacity but the muscle neither shorten or lengthens because the load is greater than the force the muscle is able to develop.
  - - - after ATP is hydrolyzed to ADP and inorganic phosphate in muscle fibers , it Is regenerated within a fraction of a second by one or more of the three pathways.
        
        Direct Phosphorylation of ADP by creatine phosphate - during vigorous excersise the need for ATP rises and stored ATP in muscles is used up within a few twitches. then creatine phosphate is tapped to regenerate ATP while other metabolic pathways adjust to the sudden high demand for ATP
        
        Anaerobic Pathway - As stored ATP and CP are exhausted, more ATP is generated by breaking down glucose obtained from the blood or glycogen stored in the muscle
        
        Lactic acid is the end product of glucose metabolism during anaerobic glycolysis. Most of the lactic acid diffuses out of the muscles into the blood stream.
        
        Aerobic Respiration - during rest and light to moderate excersise, even if prolonged, 95% of the ATP used for muscle activity comes from aerobic respiration
        
        Aerobic respiration requires oxygen and mitochondria, and involves a sequence of chemical reactions that break the bonds of fuel molecules and release energy to make ATP
  - - - ATP levels inside muscle cells do drop, but muscle fatigue serves to prevent complete depletion of ATP in muscle, which would result in death of muscle cells and rigor mortis.
      - Chemical changes involved
      - Ionic Imbalances
      - Increased inorganic Phosphate
      - Decreased ATP and increased magensium
      - Decreased glycogen