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Free STEP1 Exam Braindumps (page: 39)

Page 38 of 213
PDF with 845 Questions

Pupil size is an important indicator of brainstem function. Which of the following results in papillary constriction?

  1. atropine, a blocker of muscarinic receptors
  2. decreased parasympathetic activity of inner eye muscle fibers during darkness
  3. general increased sympathetic tone during emotional excitement
  4. increased sympathetic activity of inner eye muscle fibers during darkness
  5. phentolamine, a blocker of alpha adrenergic receptors

Answer(s): E

Explanation:

Pupil diameter is determined by the balance between sympathetic tone to the radial fibers of the iris and parasympathetic tone to the circular pupillary sphincter muscle. Sympathetic activation will result in pupillary dilation via activation of alpha-adrenergic receptors. Hence, an alpha-adrenergic blocker leads to constriction of the pupil. Parasympathetic activation on the other hand will result in pupil constriction via activation of muscarinic acetylcholine receptors, so that pupil dilation occurs as a result of a muscarinic acetylcholine receptor block (choice A). The same is true for decreased parasympathetic activity during darkness (choice B), or increased sympathetic activity, independent if the initial stimulus is due to emotional excitement or darkness (choices C and D).



For the bithermal caloric test, a measure of vestibular sensitivity, warm or cold water is introduced into the ear. This often causes vertigo and nausea as a side effect as a result of which of the following?

  1. convection currents in endolymph
  2. especially fast flow of endolymph
  3. temporary immobilization of cristae ampullares
  4. temporary immobilization of otolith organs
  5. temporary inhibition of cochlear hair cells

Answer(s): A

Explanation:

Water that is either warmer or cooler than body temperature when introduced into the external auditory meatus sets up convection currents within the endolymph of the inner ear. These currents may result in the movement of the cupula, the gelatinous matrix, which sits atop the crista ampullaris and occludes the lumen of the semicircular canal. Displacement of the cupula results in activation of the vestibular hair cells of the ampullar crista. This inappropriate stimulation of the vestibular system conflicts with sensory information from other sensor organs, including vestibular sensors on the contralateral side, vision, and proprioception, and may in turn result in vertigo and nausea. The existence of the many ducts within the inner ear might imply that the fluids that fill them are flowing through the ear. However, neither endolymph nor perilymph "flow" along their respective compartments in the normal or stimulated vestibular system (choice B). Neither hair cells of cristae ampullares (choice C) nor of otholith organs (choice D) nor of the cochlea (choice E) are temporarily immobilized or inhibited by temperature changes.



below figure shows a lead II electrocardiogram from a normal 30-year-old female at rest. If a beta- adrenergic agonist such as isoproterenol is administered intravenously to this woman, what will be her resulting heart rate in beats per minute?

  1. 40
  2. 55
  3. 65
  4. 70
  5. 90

Answer(s): E

Explanation:

From inspection of the figure, the R-R interval (time between heart beats) at rest is 0.83 seconds; 60 seconds/minute divided by 0.83 yields a resting heart rate of 72 beats/minute. Since activation of receptors in the sinoatrial node will result in increased heart rate, the only alternative larger than 72 beats/ minute is E., 90 beats/minute.



With increasing age, it is quite common for adults to have very low sensitivity for highpitch sounds. Which of the following physiologic responses occur as the pitch of a sound is increased at constant sound pressure?

  1. a greater number of hair cells become activated
  2. the amplitude of maximal basilar membrane displacement increases
  3. the frequency of action potentials in auditory nerve fibers increases
  4. the location of maximal basilar membrane displacement moves toward the cochlear base
  5. units in the auditory nerve become responsive to a wider range of sound frequencies

Answer(s): D

Explanation:

The primary change in the cochlea due to an increase in the frequency of a sound wave is a change in the position of maximal displacement of the basilar membrane. A low-pitched sound produces the greatest displacement toward the apex of the cochlea, which results in activation of hair cells at that location. As pitch increases, the position of greatest displacement moves closer to the base of the cochlea. Increases in the number of hair cells that are activated (choice A), increased amplitude of basilar membrane displacement (choice B), increases in the frequency of discharge of units in the auditory nerve fibers (choice C), and an increase in range of frequencies to which such units respond (choice E), are all more likely to be observed in response to increases in the intensity of the sound stimulus (sound pressure) rather than to increases in pitch.






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