Download Which of the following would result from stimulation of the

Which of the following would result from stimulation of the parasympathetic nervous
system?
@ Parasympathetic stimulation increases epiphora by increasing tear production by the
lacrimal gland and by contracting the nasolacrimal duct (decreasing outflow; A is
incorrect). The superior tarsal muscle is innervated by the sympathetic nervous system,
which causes contraction, but the parasympathetic nervous system doesn’t innervate
that muscle (B is incorrect). Parasympathetic stimulation allows the lens to
accommodate for near vision (C is correct), and causes the pupil to contract (miosis; D
is incorrect). Sympathetic stimulation increases aqueous humor formation;
parasympathetic stimulation increases outflow (E is incorrect).
A.
increased tear outflow through the nasolacrimal duct
B.
relaxation of the superior tarsal muscle
C.
contraction of the ciliary muscle, making the lens more rounded*
D.
mydriasis
E.
increased aqueous humour formation
In a person with presbyopia, an object that is close to the eye would be focussed:
@ Presbyopia is caused by a loss of accomodation with age, which results in an
inability to focus on near objects (they end up being focused behind the retina; C is the
correct answer). Myopia results in focusing in front of the retina; emmetropia is correct
focusing. Astigmatism occurs when the curvature of the cornea or lens is uneven,
producing images that are out of focus in some planes but not others.
A.
in front of the retina
B.
correctly everywhere on the retina
C.
behind the retina*
D.
correctly in some places on the retina, out of focus in others
Compared to cones, rods are more likely to:
@ Rods are more sensitive than cones, but have a smaller dynamic range (A and B are
incorrect). Rods have a lower critical fusion frequency (C is the correct answer). Cones
are concentrated in the fovea, while rods are distributed in the periphery (D is incorrect).
Rods respond to scattered light more than highly focussed light (which stimulate cones;
E is incorrect).
A.
have lower sensitivity to light.
B.
saturate in response to brighter light.
C.
detect a flickering light as continuous.*
D.
be concentrated in the fovea.
E.
respond to narrow axes (highly focussed) beams of light.
Which of the following is a direct step in rod phototransduction?
@ Activation of rhodopsin by a photon, in turn activates transducin which causes
GDP/GTP exchange. This activates phosphodiesterase which converts cGMP to GMP.
The reduction in cGMP concentrations closes cGMP-dependent Na<sup>+</sup>
channels, resulting in hyperpolarization. B is the correct answer.
A.
activation of transducin by a photon
B.
conversion of cGMP to GMP by phosphodiesterase*
C.
phosphorylation of GMP to GDP by transducin
D.
opening of cGMP-dependent Na<sup>+</sup> channels
E.
activation of phosphodiesterase by light-activated rhodopsin
Identify the correct statement about the visual cycle.
@ The retinal pigment epithelium (RPE) is a key component in the visual cycle,
particularly of rods (A is incorrect). 11-cis-retinal is moved into the rods during dark
adaptation, increasing the concentration of photopigment and improving sensitivity.
Atrophy of the RPE is one of the earliest stages of macular degeneration (C is the
correct answer). 11-cis-retinal (not the opsin portion of the visual pigments) is
dependent upon an adequate supply of vitamin A, and
A.
The bleaching and recycling process occurs entirely within the cytoplasm
of rods.
B.
During dark adaptation, 11-cis-retinal is moved into storage within the
RPE.
C.
Atrophy of the RPE, with its effects on the visual cycle, can result in agerelated macular degeneration.*
D.
Vitamin A deficiency decreases synthesis of one of the cone pigments,
resulting in decreased colour perception being one of the first symptoms.
E.
The visual cycle is slower in cones than in rods, which is why night
blindness occurs first in rods.
Following phototransduction,
@ Ganglion cells are the first cells in the visual pathway to generate action potentials (A
is incorrect). Bipolar cells invert the signal going to ON ganglion cells, resulting in action
potentials being generated in response to light in those cells (B is incorrect). Ganglion
cells have a divided receptive field (C is correct). Diffuse stimuli only weakly affect
ganglion cells, resulting to stimulation of ON cells and inhibition of OFF cells (D is
incorrect). Ganglion cells are stimulated by one colour of light (red, green or blue), but
inhibited by others.
A.
action potentials are generated in the bipolar cells.
B.
bipolar cells invert the signal from the photoreceptors, generating
depolarization in response to light in all ganglion cells.
C.
lateral inhibition from the amacrine cells results in ganglion cells having a
receptive field that’s divided into the center and the surround.*
D.
lateral inhibition results in an increased response of a ganglion cell to a
diffuse stimulus that fills its entire receptive field.
E.
ganglion cells are only responsive to a single colour of light.