Visual System Flashcards
optic disk
- produces
- exit of…
produced blind spot
exit of optic nerve
macula lutea
-contains
central fovea (pit)
components of retina
optic disc
macula lutea
cell layers of retina
pigment cell layer
layer of rods and cones
ganglion cell layer
retina: pigment cell layer
- derived from
- attaches retina to…
- absorbs…
derives from choroid
attaches to eyeball
absorbs stray light
rods
- location
- function
periphery of retina
function
-low light vision
-perception of movement
cones
-location
central retina
what is the name for the structure that contains only cones that is the area of maximum visual acuity, color, and brightness discrimination
fovea
retina: ganglion cell layer
- _____ of these cells form the _____
- _____ are described for ganglion cells
myelinated axons of these cells form the optic nerve
receptive fields are described for ganglion cells
in the normal eye, a _____ image of the object is focused on the retina
inverted
light is refracted by the…
-which parts inverts the image?
cornea
aqueous humor
lens (where image is inverted)
vitreous humor
lens
- function
- how does this occur?
- -what is this called
changes the refractive power of the eye
accomplished by changing the shape fo the lens
-called accommodation
how does the lens shape change for
- close viewing
- distant viewing
rounder for close viewing
flatter for distant viewing
accommodation
-to view a near object, the lens must _____ its refractive power by becoming _____
increase by becoming more convex (rounder)
at rest, how is the lens held in a relatively flat shape?
suspensory fibers that connect it to the ciliary muscle
how does the ciliary muscle react to accommodate for near vision?
-when this happens, what property of the lens allows it to contract into a more spherical shape
ciliary muscle contracts, reducing the tension on the suspensory fibers
its natural elasticity
ciliary muscle controlled by what type of nerve fibers
parasympathetic nerve fibers
emmetropia
-what is it
naturally occurring condition where the image of an object is focused on the retinal surface
what are some refractive abnormalities
hypermetropia
myopia
presbyopia
hypermetropia
- another name
- what happens
far-sightedness
focal point falls behind the retinal surface
myopia
- another name
- what happens
near-sightedness
falls in front of the retina
presbyopia
- what is it
- what is a common external accommodation for this?
loss of lens elasticity noted with age
corrective prescriptions may then include a part of the lens that corrects vision for distance and a part that corrects for near vision = bifocals
rods
- excitation threshold level
- used in _____ conditions
- rod acuity is _____
low excitation threshold
used in dim conditions
rod acuity is poor (doesn’t matter, because when light is low, you can’t see small objects anyways)
cones
- excitation threshold level
- used in _____ conditions
- acuity is…
high excitation level
used in high light conditions
acuity is high
which provide color vision: rods or cones
cones
ability to distinguish color vision is due to presence of…
three separate cone populations, each of which is maximally sensitive to a different wavelength of light
what are the difference cone populations responsible for color vision?
blue
green
red
color blindness
-results from…
absence of one or more of the cone populations
what is the rest of the retina doing that is not responsible for sensing light?
neural coding of visual signals
generator potentials
- originate…
- transmitted to…
- altered by…
originate in receptors
transmitted to bipolar cells
altered by other cells in the retina
generator potential pathway can be visualized as…
-what are they?
two separate systems
- vertical system
- horizontal system
how do signals pass in the vertical system?
from receptors to bipolar cells to ganglion cells
what happens in the horizontal system?
horizontal and amacrine cells provide lateral interactions (lateral inhibition) between the different vertical system components
ganglion cellc
-function
final stage of retinal processing
transmit information to subcortical visual centers in the brain
optic nerve is formed by what types of cells
axons of ganglion cells
receptive field of a ganglion definition
area in visual space (or the corresponding area of retinal surface) which, upon illumination, influence the signaling of that neuron
-remember on-center and off-surround
ganglion cells can be categorized on the basis of their…
response duration
morphology
“sustained” ganglion cells
- characteristic
- typically correspond with what size ganglion cells
respond as long as the stimulus remains within the receptive field
small ganglion cells (P-cells)
“transient” ganglion cells
- characteristic
- typically correspond with what size ganglion cells
respond only when the light is turned on or off
correspond with large ganglion cells (M-cells)
M-cells
-primarily concerned with…
signaling changes in the scene being viewed
-includes movement, changes in light and dark contrast, and basic form analysis
P-cells
-primary function
provide information about fine detail (high resolution analysis of image) and color
what is a visual field
the part of space that is being viewed
signals transmitted through the central visual pathways are divided into…
primary and secondary pathways
explain the concept of hemifields within the visual field
-this is accomplished at the level of the…
visual field can be divided by a vertical line at the fixation point into a left and right hemifield
each half of the brain receives information only from the opposite (contralateral) hemifield
this separation is accomplished at the level of the optic chiasm
relation bewteen binocularity and homonymity
images of the visual world are composed of information from the two eyes (binocular) which are merged to form a single image (homonymity)
homonymous
-this term, as it applies to visual fields, describes…
both eyes viewing the same or corresponding visual fields
which part of the brain is perceiving the contralateral half of the visual field
-what is this called?
primary visual cortex
called contralateral homonymous perception
everything caudal to the optic chiasm is carrying only…
contralateral homonymous sensation
hemianopia
- also called…
- what is it
also called hemianopsia
loss of visual perception of half of the entire visual field
heteronymous
-as it applies to visual fields, what does it describe
describes individual eye viewing different visual fields
if each eye is only able to see the ipsilateral temporal visual field and not the nasal visual fields, the deficit would be classified as
- give both names
- which is preferred
binasal heteronymous hemianopia
binasal hemianopia is preferred
