A champion weight lifter picks up a pencil. A minute later she picks up a sixty-pound object using the same muscles. What was different about the two movements? Also, what are the differences (at the cellular and molecular levels) in her arm muscles as compared to those of a weaker, untrained person?
What will be an ideal response?
The movement of the heavier object involved recruitment of more motor units. Those units were able to do the job because her resistance training exercise stimulated the hypertrophy of skeletal muscle cells; that is, individual cells contain more myofibrils and are capable of generating more tension during contraction. (One might also discuss the possibility that she has more powerful fast-twitch fibers and perhaps a few more muscle cells than nonathletic peers.)
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The primary target cells for GnRH are located in the
A. anterior pituitary gland. B. hypothalamus. C. genitals. D. adrenal gland. E. gonads.
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A. They dampen strong vibrations from very loud sounds. B. They amplify softer sound and sharpen pitch perception. C. They bend and depolarize with specific wavelengths of sound waves. D. All of the choices are correct.
How does lung perfusion work in ventilation-perfusion coupling?
A. Alveolar capillaries constrict where the partial pressure of oxygen is low, so blood is diverted to where the partial pressure of oxygen is high. B. If partial pressure of carbon dioxide increases, the bronchioles dilate. C. Air flow is directed to lobules where partial pressure of carbon dioxide is high. D. If partial pressure of carbon dioxide decreases, the bronchioles constrict.