Lecture 7

  1. Titin
    • -largest protein in the body
    • -binds both actin and myosin
  2. Thin Filaments
    • -actin
    • -tropomyosin
    • -Troponin complex (TnT, TnC, TnI)

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  3. TnT
    binds tropomyosin
  4. TnC
    binds Ca
  5. TnI
  6. Thick Filaments
    -myosin (head, hinge, tail region)

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  7. Myosin Head
    • Alkali Light Chain
    • Regulatory Light Chain
  8. Tropomyosin and Troponin
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    • 1. When no Ca is present tropomyosin blocks myosin binding sites on acting.

    2. When Ca enters the cell it binds TnC moving TnI out of the way and moving tropomyosin into the actin groove, freeing the myosin binding sites.
  9. Muscle Contraction : the Power Stroke
    • 1. Attached State
    • 2. Released State
    • 3. Cocked State
    • 4. Cross-bridge State
    • 5. Power-stroke State
  10. Muscle Contraction Step 1
    -Attached State to Released State
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    • When no ATP is bound, myosin is attached to actin in the 'attached state'
    • ATP binds myosin head, causing the actin and myosin to dissociate 'released state'
  11. Muscle Contraction Step 2
    -Released State to Cocked State
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    • ATP is hydrolyzed, causing the myosin heads to return to their resting conformation (45 degree angle to perpendicular to actin)
  12. Muscle Contraction Step 3
    -Cocked State to Cross-Bridge Formation
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    • Cross-bridge forms between myosin head and the actin at a new position
  13. Muscle Contraction Step 4
    -Cross bridge State to Power Stroke
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    • ADP and phosphate released the myosin is mused to left and the actin is pushed to the right = power stroke
  14. Muscle Contraction Step 5
    -Power Stroke to Attached State
    myosin is now in the attached state again with the myosin heads bound to the actin at a 45 degree angle
  15. Energy Sources for Muscle Contraction

    • In SKM generated by:
    • -glycogen pathway (bulk of synthesis)
    • -creatine posphate synthesis (a little)
  16. Summation
    If twitches occur close enough together they can summate, increasing the tension produced for a single fiber
  17. Unfused Tetnus
    There are tiny releases of muscle tension
  18. Fused tetanus
    muscle is always contracted
  19. Motor Unit Pool
    A pool consists of many motor neurons each of which innervates a motor unit within the muscle

    -if you need finer muscle control there's a smaller motor unit pool.
  20. SKM muscle tension can be varied by:
    1. Summation of twitches (tetanus)

    2. Recruiting additional motor neurons to the pool
  21. Cardiac Muscle Electrical Properties
    • 1. Automaticity (spontaneous depolarization)
    • 2. Main pacemaker = SA node
    • 3. ACh can affect HR through M2 receptors
    • 4. L type Ca channels need physical CONTACT with SR
  22. Cardiac Muscle Tension
    • -no summation
    • -contractile force varies by the magnitude of Ca increase, or the sensitivity of contractile proteins to Ca
  23. Cardiac Muscle Fiber Types
    • 1. Atrial
    • 2. Ventricular
    • 3. Conduction system
    • 4. Epicardial
    • 5. Endocardial
  24. Skeletal vs. Cardiac Muscle
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Card Set
Lecture 7
Striated Muscle