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The process by which application of a constant stimulus to the center of a receptive field
results in a gradual decrease in the generation of action potentials in second order
neurons of a sensory pathway is called:
@ Lateral inhibition occurs when a stimulus applied to the edge of a receptive field
(“surround”) causes a decrease in response. Perception is the concious detection of a
stimulus. Recruitment is the increase in the number of neurons responding as a
stimulus increases in intensity. Transduction is the conversion of stimulus energy to
receptor potentials. The correct answer is D: adaptation is the decrease in response to
a constant stimulus. When it occurs slowly, it is called tonic adaptation; rapid decreases
are termed phasic.
A.
lateral inhibition
B.
perception
C.
recruitment
D.
tonic adaptation.*
E.
transduction
According to the gate theory of pain, activation of skin mechanoreceptors causes:
@ Activation of Aβ fibres (either by activating skin mechanoreceptors or by direct
stimulation using TENS) decreases pain perception, so A and B are incorrect. Skin
mechanoreceptors don’t directly affect the endogenous opiate system, so D and E are
incorrect. Activation of skin mechanoreceptors reactivates inhibitory interneurons that
decrease activity in the second order neurons (C is correct; B is incorrect).
A.
increased pain perception.
B.
decreased activity of tonically-active inhibitory interneurons.
C.
inhibition of second order neurons in the nociceptive pathway.*
D.
decreased actions of enkephalins and endorphins.
E.
activation of the endogenous analgesic system.
A patient comes to your office exhibiting a spontaneous, conjugate, downbeat
(downward) nystagmus, which increases when the patient looks down. There is no
difference in the nystagmus when the patient is in a supine or an upright position.
Which of the following defects could explain this patient’s symptoms?
@ A downward nystagmus (fast down, slow up) in both eyes (conjugate) indicates that
the VOR is moving the eyes upward, as it normally would in response to a downward
head tilt. A downward head tilt normally activates the posterior semicircular canals,
therefore a lesion in the anterior semicircular canals would produce a similar effect (A is
the correct answer). The fact that the nystagmus does not change with position
eliminates the possibility of otolith involvement.
A.
Lesion in an anterior semicircular canal*
B.
Lesion in a posterior semicircular canal
C.
Lesion in both an anterior semicircular canal and the saccule
D.
Lesion in both a posterior semicircular canal and the saccule
Which of the following clinical tests can detect a sensorineural hearing loss?
@ Any of the tests listed would detect sensorineural hearing loss. The combination of
Rinne and Weber would allow you to determine which ear is affected. The otoacoustic
emission test would determine outer hair cell function, while the behavioural audiogram
would test the integrity of the entire auditory pathway.
A.
Rinne test
B.
Weber test
C.
Behavioral audiogram
D.
Otoacoustic emission test
E.
All of the above*
Identify the CORRECT statement.
@ Deflection of stereocilia toward the tallest stereocilia (not the shortest) causes
depolarization (A is incorrect). Outer hair cells (not inner hair cells) contract in response
to a sound stimulus (C is incorrect). The medial vestibulospinal system stabilizes head
(not eye) position during walking (the VOR maintains the visual image on the fovea), so
D is incorrect. The traveling wave establishes the frequency/place relationship (E is
incorrect). The correct answer is that opening transduction channels depolarizes hair
cells by increasing K<sup>+</sup> influx (B is correct).
A.
Movement of hair cell stereocilia toward the shortest stereocilia causes
depolarization.
B.
Opening of transduction channels causes K<sup>+</sup> ions to flow into
the hair cell.*
C.
Inner hair cells contract in response to depolarization.
D.
The medial vestibulospinal system keeps the visual image focussed on
the fovea during walking.
E.
The traveling wave establishes a pattern of intensity vs. place along the
basilar membrane.
The refractive error that occurs when images are focused in front of the retina is called:
@ ASTIGMATISM is observed when the curvature of the cornea or lens is not equal in
all meridians, causing unequal refraction and making a portion of the image out of
focus. CATARACTS cause opacity of the lens due to physical trauma, radiation, high
glucose concentration in aqueous humor of diabetic patients, or age. HYPEROPIA (farsightedness; also called hypermetropia) occurs when images are focused behind the
retina. MYOPIA (near-sightedness) occurs when images are focused in front of the
retina. PRESBYOPIA: blurred vision when reduced malleability causes a decrease in
the accommodative power of the lens (resulting in a condition similar to hyperopia)
A.
Astigmatism
B.
Cataracts
C.
Emmetropia
D.
Hyperopia
E.
Myopia*
F.
Presbyopia
Activation of rhodopsin can cause:
@ Transduction causes hyperpolarization of the photoreceptors (A is incorrect).
Recycling of rhodopsin from the RPE to the rod occurs in the dark (B is incorrect).
Phototransduction closes cyclic nucleotide-dependent Na<sup>+</sup> channels,
without affecting K<sup>+</sup> flux (D is incorrect). Action potential generation in
ganglion cells is dependent on location within the receptive field: light in the center
activates on cells, and in the suround, off cells (so activation of rhodopsin in the
surround activates on cells and in the center, off cells). Therefore C is the correct
answer.
A.
depolarization of rods.
B.
recycling of pigment from the retinal pigment epithelium to the rod.
C.
increased action potential generation in on and off ganglion cells.*
D.
increase outflow of K<sup>+</sup> from the rod.