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Directions: Each numbered item is followed by lettered options. Select the best answer to each question. Some options may be partially correct, but there is only ONE BEST answer.

General Physiology and Neurophysiology

Questions 1–2

  1. Nitrous oxide (N2O) is a lipid soluble anesthetic gas. A 14-year-old girl was sedated with N2O to relieve pain during an intra-articular injection. The N2O concentration in her blood quickly equaled, but never exceeded, the alveolar N2O concentration. What membrane transport mechanism is most likely to account for the uptake of N2O from inspired air into her blood?

    1. Antiport with CO2

    2. Cotransport with O2

    3. Endocytosis

    4. Primary active transport

    5. Simple diffusion

  2. The rate of N2O uptake would increase if the:

    1. body temperature decreased

    2. diffusion distance from alveolus to blood increased

    3. inspired N2O concentration increased

    4. rate of alveolar ventilation decreased

    5. rate of pulmonary blood flow decreased

  3. Questions 3–5

  4. What change in ion channel activity is most responsible for the rapid depolarization of the neuronal membrane potential at position 2 (shown in the above figure)?

    1. Opening of K+ channels

    2. Closure of K+ channels

    3. Inactivation of K+ channels

    4. Opening of Na+ channels

    5. Closure of Na+ channels

    6. Inactivation of Na+ channels

  5. During the repolarizing phase of the nerve action poten tial shown, which ionic currents are flowing when the membrane potential is 0 mV?

    1. Net current is zero at 0 mV

    2. Net inward K+ current

    3. Net inward Na+ current

    4. Net inward Cl current

  6. If a second depolarizing stimulus of normal strength was applied at the arrow marked A on the figure, a second action potential

    1. has a lower peak voltage than normal

    2. has slower depolarization

    3. is additive with the first action potential

    4. is normal size but initiation is delayed

    5. would not be triggered

  7. An isolated muscle was studied in the laboratory. The figure shows the relationship between shortening velocity and the total load placed on the skeletal muscle. A change in which of the following variables can explain the shift in this force-velocity relation from curve A to curve C?

    1. Increased preload

    2. Increased contractility

    3. Increased afterload

    4. Increased Vmax

  8. H+ secretion was studied in selected cells taken from the human distal colon. H+ secretion was found to be dependent on the presence of K+ in the lumen of the colon, and was completely inhibited when the tissue was deprived of oxygen. Which mechanism of H+ secretion is most consistent with the transport characteristics described?

    1. Exocytosis

    2. Facilitated diffusion

    3. H+/K+ cotransport

    4. H+/Cl antiport

    5. H+ channels

    6. H+/K+-ATPase

    7. Simple diffusion through plasma membrane

  9. A low serum K+ concentration (hypokalemia) of 2.0 mM ...

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