Biol 224 Theme 13

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Biol 224 Theme 13
2013-10-11 21:06:34
Biol 224

Theme 13
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  1. Muscle
    • -highly specialized tissue with the ability to contract in response to stimuli 
    • -a group of cells termed muscle fibers bound together by connective tissue
    • -three types of muscle, based on structure, function, and control mechanisms
    • -cardiac muscle-striated(involuntary muscle)
    • -smooth muscle-smooth(involuntary muscle)
    • -skeletal muscle-striated(voluntary muscle)
  2. Myofibers
    • -long cylindrical multinucleated cells
    • -composed of actin and myosin myofibrils repeated as a sarcomere(the basic unit of contraction, gives skeletal muscle its striated appearance)
  3. Tendons
    -connective tissue that link bones to skeletal muscle
  4. Myofibrils
    • -cylindrical organelles within muscle cells 
    • -composed of two types of filaments 
    • -thin filaments=actin
    • -thick filaments=myosin
    • -protein complex composed of actin and myosin is called actomyosin
  5. Titin
    • -AKA connectin
    • -large protein that acts as a molecular spring responsible for muscle elasticity connecting the Z line to the M 
  6. A-Band
    • -wide band of myosin
    • -contains the H zone, a narrow region in the center of the A band between the sets of thin filaments on either side
    • -contains the M line which is in the center of the H zone and contains proteins that link central regions of adjacent thick filaments
  7. Z Line
    • -two sets of thin filaments anchored to network of proteins at this point
    • -two successive Z lines make a sarcomere
  8. I Band
    -contains portions of thin filaments that do not overlap thick filaments
  9. Cross Bridges
    -extend from surface of myosin toward thin filaments
  10. Contraction of a Sarcomere

    • •Each sarcomere shortens as the thin
    • filaments slide closer together between the thick filaments;
    • •Z lines are pulled closer together;
    • •The A bands does not change as a
    • muscle fiber shortens,
    • •The I bands and H zones become
    • shorter.
    • •Sarcomeres shorten as thin filaments slide past stationary thick filaments;
    • •Myosin cross-bridges attach
    • to thin filament and force thin filament toward center of sarcomere;
    • •Cross-bridge repeats motion as long as stimulation to contract continues.
  11. Myosin
    -contains an actin binding site
  12. Actin
    • -form two intertwined helical chains(thin filament) using 
    • --Troponin-a complex of three regulatory proteins 
    • --Tropomyosin-a binding protein that regulates actin
    • -helical actin chain is intertwined with Tropomyosin(which goes in the groove of the helix) and physically cover the binding sites on the actin molecules for attachment with myosin cross bridges
    • -thin filament 2-3 times smaller than thick filament
  13. Cross Bridge Formation
    • -two heads of myosin form the cross bridge
    • -6 protein subunits of Myosin combine to form a protein with 2 heads and a long tail
    • -tail lies along axis of thick filament
    • -two heads form cross bridges
    • -each head contains a binding site for actin and ATP
    • -the heads of two subunits act in opposing directions with their tails intertwined 
    • -when the heads contract they pull on the thin filament and shorten the sarcomere
    • -the globular heads which protrude at regular intervals from the thick filament form the cross bridges 
  14. ATPase
    • -catalyze the decomposition of ATP into ADP and Pi 
    • -releases energy which is harnessed by the enzyme to drive other chemical reaction
    • -provides energy for muscle contraction
  15. Step 1-Cross Bridge Cycle
    • -cross bridge binds to actin because
    • -Ca2+ levels are high
    • -ADP and Pi complex bound to actin that become energized
  16. Step 2-Cross Bridge Cycle
    • -power stroke
    • -release of Pi cause the cross bridge to change conformation, rotating forward and moving toward the H zone
    • -filament slides
    • -ADP is released
  17. Step 3-Cross Bridge Cycle
    -ATP binds to myosin, causing cross bridge to detach from Actin
  18. Step 4-Cross Bridge Cycle
    • -hydrolysis of ATP 
    • -reenergizes the cross bridge
    • -ADP and Pi remain bound to the cross bridge
  19. Contraction Regulation
    • -regulated by the neuromuscular joint
    • -junction of motor neuron's axon and muscle fiber
    • -axon divides into terminals containing vesicles of ACh
    • -the region of muscle fiber under the axon terminal is folded into junctional area to increase surface area
    • -the nicotinic ACh receptor is a ligand gated ion channel(when ACh binds it opens)
    • -allows Na to flow into the muscle leading to depolarization and an action potential
  20. T-Tubules
    • -AKA transverse tubules
    • -invaginations of plasma membrane that conduct an AP from the outer surface to inner regions of a muscle
  21. Excitation Contraction
    • -motor neurons from somatic NS generate AP that liberate ACh
    • -ACh is secreted into neuromuscular junction and binds to nicotinic receptors in the muscle cell membrane
    • -Ca2+ is liberated from the sarcoplasmic reticulum 
    • -Ca2+ binds to troponin which changes shape and forces the tropomyosin off of the actin active site(this allows myosin to form cross-bridges with active actin)
    • -allows 4 steps of cross bridge to complete muscle contraction
  22. Slow Fibers
    • -have myosin with a lower ATPase activity(changes how fast it hydrolyzes ATP)
    • -maximal force produced by each(fast/slow) only speed varies
  23. Fast Fibers
    • -contain myosin with high ATPase activity(changes how fast it hydrolyzes ATP) 
    • -maximal force produced by each(fast/slow) only speed varies
  24. Oxidative Fibers
    • -contain large number of mitochondria
    • -high capacity for oxidative phosphorylation
    • -surrounded by many small blood vessels
    • -contains large amounts of myoglobin(oxygen binding protein) for intracellular reservoir of oxygen
    • -ATP production depends on blood flow to deliver oxygen and nutrients
    • -"dark" meat on a turkey
  25. Glycolytic Fibers
    • -few mitochondria but high concentration of glycolytic enzymes and large stores of glycogen
    • -limited use of oxygen
    • -few blood vessels
    • -little myoglobin=pale color 
    • -"white meat" on turkey
  26. Slow Oxidative Fibers
    • -have low rates of myosin ATPase, but have ability to make large amounts of ATP
    • -do not fatigue easily
    • -used for prolonged, regular activity(flight, long distance swimming)
    • -gives red color to breast meat on ducks, which use the muscles for flight
  27. Fast Oxidative Fibers
    • -high myosin ATPase activity and can make large amounts of ATP
    • -do not fatigue quickly and can be used for long-term activity
    • -particularly suited for rapid actions(rapid sounds made by throat muscles on birds, clicking of rattlesnakes tail)
  28. Fast Glycolytic Fibers
    • -high myosin ATPase activity but cannot make as much ATP as oxidative fibers, because source of ATP is glycolysis 
    • -best suited for rapid, intense actions(short sprint, cat pouncing on prey)
    • -fatigue quickly compared to oxidative fibers(breast meat on chicken is white because unlike ducks chickens only fly short distances and do not have oxidative pectoral muscles)
  29. Exercise
    • -can produce increase in size of muscle fibers
    • -increase capacity for ATP production
    • -number of cells remain the same
    • -individual fibers grow which account for the size increase
  30. Aerobic Exercise
    • -low intensity, long duration
    • -increases number of mitochondria in slow oxidative fibers
    • -number of blood vessels around the fibers increases to supply the greater energy demands
    • -increase endurance capability
  31. High Intensity Exercise
    • -short duration 
    • -affect fast glycolytic fibers
    • -fibers increase in diameter becasue new actin and myosin filaments are made, creating more myofibrils 
    • -glycolytic activity is enhanced by elevated synthesis of glycolytic enzymes
    • -high strength/low endurance training
  32. Atrophy
    • -loss of muscle due to cessation of muscular activity
    • -denervation atrophy occurs when the neurons to skeletal muscle are destroyed and muscle fibers will progressively shrink in diameter
    • -can occur in long periods of disuse, cast of broken limb