Human Physiology, 14th edition (2016)

(Tina Sui) #1
Muscle 403


  1. How is electrical excitation of a skeletal muscle fiber
    coupled to muscle contraction? Speculate on why the exact
    mechanism of this coupling has been difficult to determine.

  2. How would a rise in the extracellular Ca^2 1 concentration
    affect the beating of a heart? Explain the mechanisms
    involved. Lowering the blood Ca^2 1 concentration can cause
    muscle spasms. What might be responsible for this effect?

  3. Organs consisting mostly of highly differentiated cells
    appear to also contain small populations of multipotent,
    adult stem cells (chapters 3 and 20). Explain the significance
    of this statement, using skeletal muscles as an example.

  4. Explain how contraction of a myocardium is analogous to
    a skeletal muscle twitch, and why the myocardium cannot
    exhibit summation and tetanus.

  5. Explain how the organization of actin and myosin in smooth
    muscle cells differs from their organization in striated
    muscle cells, and the advantages of these differences.


Test Your Quantitative Ability
Refer to figure 12.22 to answer the following questions.


  1. Which energy source varies the least during different
    intensities and durations of exercise? What is the range of its
    percentage of energy expenditure?

  2. Which energy source varies the most during different
    intensities of exercise? What is the range of its percentage of
    energy expenditure?

  3. What percentage of the energy expenditure is due to free
    fatty acids when a person (a) does mild exercise for 90 to
    120 minutes; and (b) does heavy exercise from 0 to
    30 minutes?

  4. Following exercise of which intensity and duration are the
    muscles most depleted in stored glycogen?


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