EXAM 3: BIO&251 (Chapter 10: Part 2)

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EXAM 3: BIO&251 (Chapter 10: Part 2)
2015-11-28 18:59:37
Part two of the lecture
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  1. Tension Production - MUSCLE FIBER
    • All-or-none Principle: For a given "dose" of Ca2+, all sarcomeres within a muscle fiber contract together.
    • More active cross-bridges → more tension produced

    • 1. Fiber length at time of stimulation (Affects overlap between actin and myosin)
    • 2. Frequency of stimulation (Affects duration of high [Ca2+])
    • 3. Fiber diameter (Affects amount of actin and myosin available)
  2. Tension Production - WHOLE MUSCLE
    More tension produced by individual fibers and more fibers contracting → stronger whole muscle contraction

    • Factors
    • 1. Internal and External Tension (Series elastic component [stretch in CT])
    • 2. Rectruiment (Number of active motor units)
    • 3. Muscle Size (Number of muscle fibers present)
  3. Tension Production in Muscle FIBER
    • Fiber length affects overlap between actin and myosin
    • There is an optimal length for a fiber at which force generation is maximal.
  4. Effect of Sarcomere Length on Tension
  5. Effects of Stimulation Frequency
    • 1. Single Stimulus (Simple Twitch)
    • 2. Multiple Stimuli (Treppe, Summation, Incomplete Tetanus, Complete Tetanus)
  6. The Simple Twitch
    • Latent Period: Ca2+ release from SR, "Slack" taken out of system called Series Elastic Component (Contractile elements, tendons in whole muscle)
    • Contraction Period: Tension Increases
    • Relaxation Period: Tension decreases, passive process follows pumping of Ca2+ back into SR, passive process
  7. Treppe (Staircase)
    • Also called "warm up effect"
    • Gradual increase in strength of contraction with the same stimulus

    • Factors:
    • 1. Increased Ca2+ available (No time to pump it all back into SR)
    • 2. Muscle fiber warms up (Enzymes more efficient at higher temp)
  8. Summation
    Repeated stimulation before relaxation phase has been completed → stronger contraction

    • Wave Summation: one twitch is added to another
    • Incomplete Tetanus: muscle doesn't relax completely
    • Complete Tetanus: relaxation phase is eliminated
  9. Summation Mechanism
    Stronger contractions (summation) probably due to:

    • Prolonged presence of Ca2+
    • Action Potential (AP) duration vs. contraction duration:
    • *AP is short
    • *Contraction is longer
    • *So another AP can stimulate the muscle before the contraction phase has ended
  10. Wave Summation
    • Occurs when successive stimuli arrive before the relaxation phase has been completed.
  11. Incomplete Tetanus
    • Occurs if the stimuli frequency increases further. Tension production rises to a peak, and the periods of relaxation are very brief.
  12. Complete Tetanus
    • The stimulus frequency is so high that the relaxation phase is eliminated. Tension plateaus at maximum levels.
  13. Internal and External Tenstion - Series Elastic Component
    • Internal Tension
    • *Tension generated inside contracting muscle
    • *Myosin pulling on actin in sarcomere

    • External Tension
    • *Tension generated on extracellular fibers
    • *Endo-, peri-, and epimysium form tendons
    • *Tendons stretch (Series Elastic Component)
  14. Internal and External Tension
    • Simple Twitch and Tetanus
    • SEC = Series Elastic Component
  15. Motor Units in a Skeletal Muscle
  16. Muscle Tone
    At least some of the motor units of a muscle are active at any one time, even at rest.

    • Which motor units are active varies
    • Does not produce movement, but generates muscle tone

    • Muscle Tone:
    • Stabilizes bones and joints
    • Maintains body position
    • Allows more rapid activation of whole muscle
  17. Contraction Types
    • 1. Isotonic: Means "same tension"
    • Whole muscle's length changes
    • a. Concentration Contraction (Tension>Load, Muscles shortens)
    • b. Eccentric Contraction (Tension<Load, muscle lengthens [stretches] while contracting)

    • 2. Isometric: Means "same length"
    • Muscle's length does not change, but individual fiber lengths do shorten
    • Tension is not greater than the muscle load
  18. Resistance and Speed of Contraction
    • Contraction velocity is inversely proportional to resistance.
    • High resistance (heavy weight) leads to slow contraction speed.
    • Fairly obvious from everyday life!
    • Each muscle has optimum combination of speed and load.
  19. Muscle Contraction Requires Lots of ATP
    • Energy-producing systems in a muscle:
    • *Phosphagen system (ATP and CP reserves)
    • *Glycolysis (Glycogen-lactic acid system)
    • *Aerobic system
  20. Phosphagen System
    • Found only in muscle cells
    • Involves creatine phophate (CP) and ATP
    • A FAST, SHORT-TERM method of ATP gerneration
    • *Involves only 1 enzyme (creatine phosphokinase), not a long pathway

    CP+ADP+H+↔ creatine+ATP

    • ATP is used for muscle contraction
    • Creatine is only in muscle cells
    • Total is enough for maximal burst of about 15 sec.

    Allows time for other systems to "kick in."
  21. Glycolysis
    • Used after phosphagen system during burst activity
    • *Is the first part of aerobic pathway, BUT does not require oxygen (anaerobic)

    • Anaerobic metabolism leads to H+ buildup
    • *Decreases muscle cell pH
    • *Affects enzyme function

    Can provide maximal burst of energy for about 2 minutes
  22. Aerobic System
    • REQUIRES oxygen delivery to mitochondria
    • *Krebs Cycle/Electron Transport Chain
    • *Inolves a multi-enzyme pathway

    • Resting Muscle
    • *Use fatty acid as a substrate (ATP)

    • Active Muscle
    • *Use pyruvate from glyocolysis as substrate
    • *Glycogen→glucose→(glycolysis)→pyuvate
    • *Pyruvate-(mitochondria)→Aerobic ATP generation
    • *Provides energy for long-term exercise (Marathon run=almost all aerobic)
  23. Energy Use and Level of Muscular Activity
    Resting muscle 

    • Low ATP demand
    • Lots of Oxygen available to mitochondria
    • *Surplus ATP→CP RESERVES
    • *Surplus glucose→glycogen RESERVES
    • Use fatty acids from blood for energy production
  24. Moderate Activity
    • Increased demand for ATP
    • Increased demand for O2, but O2 delivery still matching O2 demand by mitochondria.
    • Aerobic metabolism still active
    • Muscle glycogen→glucose→pyruvate→ATP


    • Also use fatty acids (and amino acids)
    • No surplus ATP so no new CP is produced (not enough left over).
  25. Peak Exercise
    O2 deliver cannot meet O2 demand

    • Anaerobic Metabolism
    • Mitochondrial ATP production very low (about 1/3 of total needed) due to low oxygen levels
    • ATP production is via glycolysis (decreased cellular pH helps limit exercise duration)
  26. Muscle Fatigue
    • Normal Function Requires:
    • 1. Energy Reserves
    • 2. Blood Supply (Deliver O2, Nutrients/Carry away wastes [CO2, heat, etc.])

    • Factors leading to muscle fatigue:
    • 1. Low energy reserves (Low substrate)
    • 2. Low pH, which effects
    • *Changes in enzyme acitivty
    • *H+ displaces Ca2+ from troponin
    • *H+ interferes with hemoglobin reoxygenation
    • 3. Central Fatigue 
    • *pH effects on brain
    • *Pain effects on brain
    • *Recover faster when performing a "diverting" mental activity
    • 4. Other factors
    • *Sarcolemma, SR damage
    • *Increase in ADP
  27. Recovery After Exercise
    • Return muscle cell conditions to resting levels
    • Return oxygen consumption rate to resting levels

    • Resting mechanism include:
    • 1. Lactic acid removal/recycling
    • 2. Excess postexercise oxygen consumption (EPOC)
    • 3. Heat Loss (sweating, vasodilation)
  28. Lactic Acid Removal/Recycling
    Fate of Lactic Acid depends upon severity of exercise

    • 1. Moderate Exercise
    • *Glycogen stores and blood glucose not severely depleted
    • *Lactate→Pyruvate→Mitochondria→energy for recovery from exercise
    • *This is the usual fate of lactate

    • 2. Severe, prolonged exercise
    • *Glycogen and glucose depleted
    • *Lactate to liver, converted to glucose→muscle cells→Glycogen (Cori cycle)
  29. Excess Postexercise Oxygen Consumption (EPOC)
    Oxygen consumption does not return to resting levels immediately after exercise. Some reasons:

    • 1. ATP is required to restore CP levels, and go from lactate to glucose to glycogen
    • 2. Sweat glands active (using ATP)
    • 3. Effects of exercise on the mitochondria
    • *Mitochondria less efficient at using O2 for ATP production
    • *Ca2+ leaks into mitochondria, must be pumped out
    • 4. Myoglobin must be reoxygenated
    • 5. Epinephrine causes leakage of Na+ into and K+ out of cells
    • *Must be pumped back out or in
    • 6. Increased body temperature→increased reaction rates→increased ATP consumption

  30. Types of Skeletal Muscle Fibers
    • Slow Fibers: "dark meat", Type l, red, slow twitch, slow oxidative
    • Intermmediate Fibers: Type ll-A, FR (fast resistant, fast twitch oxidative)
    • Fast Fibers: "white meat", Type ll-B, white, FF (fast fatigue), fast-twitch glycolytic.
  31. Physical Conditioning
    • Percentages of Fast and Slow fibers are genetically determined. Training can cause:
    • *Fast Fibers↔Intermmediate Fibers
    • *Slow Fibers↔Intermmediate Fibers

  32. Anaerobic and Aerobic Endurance
    • Anaerobic, limited by:
    • *ATP/CP availabibity
    • *Glycogen availability
    • *Tolerance for acidosis

    • Aerobic, limited by:
    • *Oxygen delivery to mitochondria (Cardiac Output, Capillary Density)
    • *Number of mitochondria
    • *Aerobic substrate availablilty