visual physiology Flashcards
what is the first site of refraction and is it fixed or variable
cornea
fixed
what is the second site of refraction and is it fixed or variable
lens
variable
how does a rounder lens affect refraction
more refraction
how does curvature of the lens increase
ciliary m. contracts => suspensory ligaments loosen => natural recoil, rounded lens
how does curvature of the lens decrease
ciliary m. relaxes => suspensory ligaments tighten, flattening the lens
is increased or decreased refraction used for far vision
decreased (lens is flattened)
for near vision, is lens curvature increased or decreased
increased (refraction is increased)
what are the three steps of the near response
- constriction of ciliary ms
- convergence of eyes to focal point
- pupillary constriction
how does pupillary constriction contribute to near vision
less light enters, eliminating diverging light rays and allowing better focus
what are the three types of vertially oriented cells in the retina
- receptor cells
- bipolar cells
- ganglion cells
are melanopsin ganglion cells horiztonally or vertically oriented
vertically oriented
what are the two types of horizontally oriented cells in the retina
- horizontal cells
- amacrine cells
do rods or cones facilitate vision in dim light?
rods
what aspect of the rod system allows increased sensitivity in dim light
convergence - many rods and bipolar cells converge on one ganglion cell
what aspect of the cone system allows maximal acuity
less convergence - one cone and bipolar to each ganglion cell
where does cone density peak
the fovea
where does rod density peak
20 degrees off center
what is the relationship of glumate release by rods and cones to light
inverse relationship - less light, more glutamate released
photons stimulate what in the rods and cones
hyperpolarization
what occurs if the center of an on-center bipolar cell’s receptive field is activated
depolarization of the bipolar cell
what occurs if the periphery of an on-center bipolar cell’s receptive field is activated
hyperpolarization of the bipolar cell secondary
what occurs if the periphery of an off-center bipolar cell’s receptive field is activated
depolarization of the bipolar cell
what occurs if the center of an off-center bipolar cell’s receptive field is activated
hyperpolarization of the bipolar cell
how do amacrine cells assist in low-light vision
inhibit competing visual pathways using GABA/glycine
what cells tell where an object ends
off-center cells
what are the 5 direct targets of the retina
superior colliculus lateral geniculate body (LGN) pretectum accessory optic nuclei (AON) hypothalamus
what target of the retina controls eye motions to converge on point of interest
LGB
what target of the retina controls focus of the eyes based on distance and determines relation position of objects
LGB
what target of the retina detects movement relative to an object
LGB
what brodmann area is the peristriate cortex
19
what brodmann area is the parastriate cortex
18
what layer of the primary visual cortex receives input from the LGB
IV
what are the main output layers of the primary visual cortex
V and VI
what are ocular dominance columns
groups of cells in the primary visual cortex that preferentially respond to one eye over the other
what are blobs
regions of neurons in the primary visual cortex that are sensitive to color
what is the major function of VI (the primary visual cortex)
identification of edges and contours
what is the major function of V2
depth perception
what is the major function of V3a
identification of motion
what is the major function of V4
processing of color input
what is the function of the dorsal pathway
“where” - associating vision with movement
through what structures does the dorsal visual pathway pass
primary visual cortex => through V3 => parietal/frontal cortex
what is the function of the ventral visual pathway
“what” - naming and recognizing objects
through what structures does the ventral visual pathway extend
primary visual cortex => inferior temporal cortex
what are the non-image-forming light-responsive cells?
MG (melanopsin ganglion cells)
what is the function of melanopsin ganglion cells
regulation of circadian rhythm
where do MG cells project their axons
to the suprachiasmatic nucleus within the thalamus
