Muscle Physiology Chapter 11

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  1. Functions of Skeletal Muscle
    • Produce movement
    • Maintain body posture/position
    • Support soft tissues
    • Guard entrances and exits
    • Maintain body teperature
  2. Types of Movement
    • Concentric and eccentric isotonic contractions
    • Flexion
    • extension 
    • abduction (towards body)
    • addutction (away from body)
  3. Isometric contractions
    helps maintain body posture and body position
  4. Maintaining body temperature
    • Shivering (warm up)
    • Vasodilation (cool down)
  5. 5 levels of muscle organization (large to small)
    • body
    • fascicles
    • fibers
    • myofibrils
    • sacromeres
  6. myofibrils
    • made from sacromeres in series
    • from 2 proteins
    • myosin and actin
  7. m line
    myosin backbone
  8. z line
    actin backbone
  9. thin filament
  10. thick filament
  11. contraction
    • sliding of myosin and actin
    • z lines move closer
  12. myosin (thick filament)
    • made of proteins
    • looks like 2 golf clubs twisted together
    • actin binding site
    • ATP site
    • hinge
    • High engery (big angle)
    • Low engery (small angle)
  13. Actin (thin filament)
    • looks like 2 strands of pearls twisted together
    • Tropomyosin (thread-like protein)
    • Troponin (found in intervals)
    • G-actin (myosin binding sites)
  14. how Ca++ regulates binding sites on actin
    Ca++ released from sarcoplasmic reticulum

    Ca++ binds to troponin complex

    Tropomyosin moves off the myosin binding sites of the actin filament
  15. Resting states of Actin
    Myosin binding sites are covered by tropomyosin
  16. Muscle about to contract
    • Binding site of actin is exposed due to Ca++ released from S.R. and shifting tropomyosin off  
    • g actin
  17. 10 steps in mechanism of muscle contraction
    • 1. Ca++ released from S.R., binds to troponin, causes active sites on actin to be exposed
    • 2. ATP binds to myosin head
    • 3. ATP hydrolyzed to ADP and Pi (still bound by myosin)
    • 4. Myosin head goes into high energy state ("cocked")
    • 5. Myosin head attaches to active site of actin molecule
    • 6. Pi is released from myosin head
    • 7. Myosin head goes to low energy state, producing "power stroke"
    • 8. Myosin and actin in rigor state and ADP is released from myosin head
    • 9. New ATP binds to myosin head and detaches from actin filament (rigor state ends)
    • 10. Repeats from #2
  18. Entire mechanism of muscle fiber contraction
    • 1. Action potential down motor neuron
    • 2. Acetylcholine (ACh) is released by neuron
    • 3. ACh binds to nicotinic receptors Na+ influx & K+ efflux (net depolarization of cell)
    • 4. New action potential propagates along muscle fiber
    • 5. Action potential enters fiber via transverse tubules
    • 6. Ca++ channels open in S.R. releasing Ca++ into cytosol
    • 7. Ca++ binds to troponin, causing tropomyosin to slide off active sites on actin filaments
    • 8. Molecular mechanism of actin and myosin movement occurs
  19. Muscle Mechanics: The Twitch
    • 1. Latent phase
    • 2. Contraction phase
    • 3. Relaxation phase
  20. Latent phase in muscle twitch
    • 1. action potential travels along muscle fiber and into the t-tubules
    • 2. Ca++ channels in SR open
    • 3. Ca++ floods into cytosol
    • 4. Ca++ binds to troponin
    • 5. Tropomyosin moves off of myosin binding sites on actin
  21. Contraction phase of twitch
    • 1. Myosin head attach to the actin and do the "power stroke"
    • 2. Myosin heads bind a new ATP, release from the actin, recock, reattach, and perform another "power stroke"
    • 3. Repeats a few times

    Increase in tension, depending on muscle fiber can last 50 ms
  22. Relaxation phase in muscle twitch
    • 1. Ca++ is pumpled back into SR
    • 2. tropomyosin covers up the myosin binding sites on actin
    • 3. myosin is no longer able to bind to actin

    Decreases in tension and depending on muscle fiber can last 50 ms
  23. Fused (complete) tetanus
    Can't see where action potentials are because they are so close together
  24. Twitch summation
    you can see on the graph where a bump is, is where and action potential has occured
  25. Unfused tetanus
    a sustain contraction, action potentials keep occuring and keep seeing bumps as tension increases
  26. Isotonic contraction
    • Lifting weights (same tension)
    • 1. straining (concentric)
    • 2. Tension (plateau)
    • 3. Shortening length (eccentric)
  27. Isometric Contractions
    • Strain against load
    • muscle fibers never shorten
    • Never enough tension to lift load
  28. True or False: Does an isotonic contraction progress to am isometric contraction as the load placed upon the muscle increases?
  29. Motor Units
    A group of muscle fibers that are all controlled by the same motor neuron.
  30. Motor units vary in size
    • Extraocular muscles (fine dexterity)
    •     few muscle fibers per motor unit

    • Gastrocnemius (leg)
    •    thousands of muscle fibers per motor unit
  31. What is motor unit recruitment?
    the turning on of more then one motor unit to complete an action

    small motor units recruit first then larger ones
  32. What is motor unit rotation?
    the switching or changing of motor units to prevent muscle fatique
  33. "Size Principle" of motor unit recruitment
    Use small first the progressively larger are recruited.

    Motor neurons that control certain muscles are controlled by interneurons in CNS 

    Interneurons begin to fire, and motor neurons with smaller cell bodies will reach -55 mV (threshold) before (few EPSPs) motor neurons with larger (more EPSPs) cell bodies

    small motor units are innervated by smaller neurons with smaller cell bodies, thus fire first in sequence
  34. Load and shortening velocity for skeletal muscles
    the more load we put on muscles the shorter the shortening velocity

    remember velocity is the change in distance over the change in time
  35. 3 Engery sources for muscle contraction
    • 1. phosphagen system
    • 2. Glycogen-lactate system (anaerobic)
    • 3. Aerobic system
  36. Phosphagen system
    • ATP & phosphocreatine (PC)
    •    creatine-PO4 + ADP -> Creatine + ATP

    Rate of energy release: 4 moles of ATP per min

    Size about 10 s (3 s of ATP and 6 s of PC)
  37. Glycogen-lactate system (anaerobic sytem)
    Glycolysis & fermentation

    sugar -> pyruvate -> lactate

    Rate of energyy release: 2.5 moles

    Size about 90 s
  38. Aerobic system
    Doing all the steps of cellular respiration

    Glycolysis, pyruvate decarboxylation, citric acid cycle, and the electron transport chain

    O2 + Sugar -> CO2 + Water

    Rate of energy release: 1 mole of ATP/min

    unlimited duration, as long as nutrients last
  39. Classification of muscle fibers
    Type 1 (slow-oxidative)

    Type 2a (fast-oxidative)

    Type 2x (fast-glycolytic)
  40. Oxidative
    likes using oxygen and aerobic reserviors
  41. Type 1 (Slow-oxidative)
    • Slow myosin ATPase
    • Slow contraction
    • Longer time to fatique
    • High use oxygen
    • Low use glycolysis
    • Many mitochondria
    • Many capillaries
    • Lots of myoglobin
    • Red color
    • Low glycogen content
  42. Type 2a (fast-oxidative)
    • Fast myosin ATPase
    • Fast contraction
    • intermediate time to fatigue
    • high oxygen use
    • intermediate glycolysis
    • many mitochondria
    • many capillaries
    • alot of myoglobin
    • red in color
    • intermediate glycogin content
  43. Type 2x (fast-glycolytic)
    • Fast myosin ATPase
    • fast contraction
    • short time to fatique
    • low oxygen use
    • high glycolysis use
    • few mitochondria
    • few capillaries
    • less myoglobin
    • white in color
    • high glycogen
  44. Muscle fatique
    • Oxidative fibers
    •   glycogen depletion and increased temperature

    • Fatigue of glycolytic fibers
    •   Possible accumulation of lactate, mechanical injury to muscle fiber, lack of blood supply and increased temperature

    • True neuromuscular fatique
    •    depletion of ACh from motor neuron termini, and only occurs in artificially stimulated neurons and muscle fibers.
  45. Torque
    Produced by a load around a joint is equal to the torque produced by the muscle around the same joint.

    Is equal to the force on a lever multiplied by the length of the lever arm.

    T = ( r X F)
  46. True or False: Skeletal muscles have a mechanical advantage because they can produce a force less then the actual force that gravity is directly producing on the load.
    FALSE, skeletal muscles have a mechanical distadvantage and must produce a force in  excess of the actual force that gravity is directly producing on the load.
  47. Mechanical disadvantage of bones and muscles as levers and forces
    The mechanical disadvantage permits a small (and slow) shortening of the muscle to result in the long (and fast) movement of a load.
  48. Where is smooth muscle found?
    • (Autonomic Nervous System)
    • digestive tract
    • blood vessels
    • bronchioles of lungs
    • eye (iris and ciliary body)
    • reproductive and urinary tract
  49. Smooth Muscle
    • Found in hollow organs and tubes
    • a cell has a single nucleus
    • shorter than skeletal muscles
    • develops tension slowly and relaxes slowly, resulting in longer contractile response (twitch)
    • Not striated (actin/myosin not arranged)
    • actin filaments radiate out of "dense bodies"
  50. Contraction of smooth muscle
    • regulated by Ca++
    • No troponin 
    • instead uses calmodulin to control muscle contraction (movement is not predictable)
  51. Signal Transduction for Smooth Muscle Contraction
    • 1. Ca++ enters cytosol from extracellular fluid and from SR
    • 2. Ca++ binds to calmodulin in cytosol
    • 3. Ca-calmodulin activates myosin light chain kinase 
    • 4. Myosin heads are activated (phosphorylated) by MLCK
    • 5. Phosphorylated myosin attaches to actin filaments and completes the "power stroke"

    Takes time to turn on/off because of enzymes
Card Set
Muscle Physiology Chapter 11
Overview for Professor Linton's Human Physiology at the University of Utah Chapter 11
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