Vision Flashcards
(107 cards)
0
Q
light collection
A
light in environment is collected and focused by the eye on photoreceptors
1
Q
4 stages of visual perception
A
1) light collection- eye
2) transduction- retina
3) neural processing- retina
4) neural processing- visual cortex
2
Q
transduction
A
light entering eye is converted into an electrical signal (transduction) by a specialized set of retinal neurons called photoreceptors
3
Q
neural processing-retina
A
information is extracted from the electrical signals before it then sent through optic nerve to the lateral geniculate nucleus of brain
4
Q
neural processing- visual cortex
A
additional information is extracted from image in a variety of cortical areas
5
Q
compound eye
A
large number of collectors funnel the light onto sheet of receptors in insects
–advantage: motion detection, operates over a wide range of wavelengths, sensitive to polarized light
6
Q
refractive eye
A
image is formed on retina by refraction through lenses
vertebrates–>resolving power
7
Q
how can you increase resolution of compound eye?
A
increasing the number ommatidia (number of cells)
8
Q
3 layers of eye
A
outer layer
choroid layer
retina
9
Q
outer layer
A
sclera– outer white layer surrounding most of eye ball; shape and support
cornea- major refractive element of eye
10
Q
limbus
A
junction of cornea and sclera
11
Q
choroid layer
A
pigment epithelium & blood vessels supply oxygen and nutrients to retinal cells
iris- controlling diameter of pupil
12
Q
retina
A
contains photoreceptors
–responsible for the initial detection and processing of light stimuli
13
Q
cornea
A
cornea–most refractory/focusing power
14
Q
anterior chamber is filled with
A
aqueous humor
15
Q
what produces aqueous humor?
A
ciliary epithelium
at a rate of 2 microliters/minute, enough to replace all of the aqueous humor 10-20 times perday
16
Q
where does aqueous go after anterior chamber
A
venous circulation via trabecular meshwork in the canal of schlemm
17
Q
if canal of schlemm gets blocked…
A
fluid build up and increased pressure in eye
- > pressure can build up enough to impede blood flow to optic nerve and retina –>blindness
- *one of causes of glaucoma
18
Q
glaucoma is associated with
A
optic nerve damage and loss of peripheral vision
19
Q
size of pupil is controlled by
A
smooth muscles in iris–circular sphincter muscle fibers and the radially-organized dilator muscle fibers
20
Q
changes in diameter of pupil change the
A
amount of light entering the eye
–depth of field
21
Q
when pupil is constricted
A
depth of field increases
less light goes through
22
Q
lens is the..
A
refractive element of eye
23
Q
accomodation
A
changing the refractive power of the lens
24
ciliary muscles
shape of the lens is controlled by the amount of tension on it
(tension- wants to flatten, elasticity- wants to keep it rounded)
controlled by PS nervous system
25
when ciliary muscles contract
decreases tension on lens and lens gets more spherical
| -->near vision, most refractive power
26
for viewing distant objects
muscles relax, lens is stretched so it is even flatter and thinner, least refractive index
27
by age 60
usually no lens accomodation left
28
myopia
eyeball too elongated, cornea too curved
| focal plane is in front of retina-->near sighted
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hyperopia
focal plane falls behind retina (not enough refractive power)
eye ball is flattened--->hyperopia
30
cancave lenses
subtract refractive power
| --used for myopia
31
convex lenses
add refractive power
| --used for hyperopia
32
cataracts
lens gets opaque in spots and interferes with vision
| lens is made up of lens fibers--long, thin cells are filled with long, fibrous water soluble proteins-->crystallins
33
when the light goes through the retina
absorbed by photoreceptors OR passes through and hits pigmented epithelium lining back of eye
34
pigmented epithelium
composed of cells packed with black pigment melanin, which absorbs any light not captured by retina
- -prevents the light from being reflected from teh back of the eye into the retina and distorting the image
- -also plays a role in recycling of the photosensitive visual pigments and int he phagocytosis of the photoreceptor tips
35
part of retina where light is usually focused
fovea (small indentation of retina)-greatest visual acuity
36
why does fovea have greatest visual acuity
cone photoreceptors (better resolution than rods) predominate here
photoreceptors are closely packed there (density is highest there)
other neuronal cells of retina are pulled to the side, so ight doesnt have to go through them, resulting in less distortion
37
blind spot
small round area of retina that has no photoreceptors
| --where the ganglion cells group together adn leave the eye (forming optic nerve)-->called optic disk
38
tapetum
nocturnal animals
behind retina that contains GUANINE crystals and is highly reflective--reflects light back through retina and provides photoreceptors with a "secnd change" to capture it
-->therefore, increases SENSITIVITY of eye to light and enhances night vision, but DECREASEs acuity
39
retinal detachment
junction between pigmented epithelium and photoreceptor layer is a weak point
-->problematic because photoreceptors not in the right focal plane and because tehy are not near their source of blood supply and nourishment
40
development of eye
optic stalk invaginates to form optic cup-->out layer becomes pigmented epithelium and inner layer becomes neural retina
ectoderm invaginates and forms LENS Vescile-->lens
41
macular degeneration
loss of pigment epithelium cells and eventually photoreceptors- wet and dry form
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macular degeneration wet
involves tissue degradation and abnormal blood vessel growth
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dry
involves deposition of yellowish protein and lipid aggregates called "drusen"
44
retina and photoreceptors are part of the ..
CNS
45
retina and neurons derived from
neural ectoderm
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5 major classes of neurons in retina
```
photoreceptor cells
bipolar cells
horizontal cells
amacrine cells
ganglion cells
```
47
light getting to photoreceptors
light coming in travels through ALL cells before hitting photoreceptors
--unmyelinated layers, so they do not interfere or scatter to distort the image
48
in the fovea, non-photoreceptor elements
shifted to the side so that the light has a more direct pathway to the receptor cells
-->less distortion and increased acuity in the foveal region
49
two types of photoreceptor cells
rods
| cones
50
both rods and cones consist of
synaptic terminal
inner segment (nucleus & most of cellular synthetic machinery)
outer segment
51
outsegment is connected to inner segment via
thin stialk/cilium that contains microtubules
- ->filled with membranous disks that contain photopigments
rods: disks pinch off and become free floating
cones: remain connected to plasma membrane
52
rod + disks
each segment contains 1000 disks and disk membranes contain photopigments (100 million)
53
photoreceptors do not
divide, however they constantly renew at a rate of ~3 disks/hour
54
phagocytosis of photoreceptor disks
at very tip, pigment epithelium cells phagocytotic activity removes discarded tips
55
characteristics of rods
more sensitive than cones in detecting light
| mediate night vision
56
why are rods more sensitive than cones in detecting light?
have more photopigment and are longer, therefore are better at capturing light
amplify light signals more than cones-- fewer photons needed to saturate response of rods
large amount of convergence with rods--many rods converge on a given bipolar cell in the retina--increases sensitivity with loss of resolution
57
4 characteristics of cones
mediate day vision
better temporal resolution
better spatial resolution
color vision
58
cones are more sensitive to
direct axial rays of light
59
rods are more sensitive to
diffuse scattered light
60
better resolution with cones beacuse
less convergence in cones system
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human eye is sensitive to wavelengths..
between 400 and 750 nm
| blue-->green-->red
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where are the cones located
the fovea (no rods there(
63
in reponse to light, photoreceptors
hyperpolarize
64
in the dark..
incrase in cGMP-->more cGMP gated cation channels in outer seg open-->increase in Na, ca into cell-->depol-->inc NT release
65
in teh light
decrease in cGMP-->more cation channels closed-->decrease Na, Ca into cell-->hyperpolarization-->decrease NT release
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to get to hydrolyze cGMP
rhodopsin binds transducin-->releases GDP, uptakes GTP by a subunit-->activates phosphodiesterase-->hydrolyzes cGMP
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adaptation
feedback mechanism where Ca inhibits guanylate cyclase
68
in response to sustained level of intense illumination
all cation channels are shut down
| cell hyperpolarizes to almost eq potential for K
69
to change set point, you can change
rate of synthesis of guanylate cyclase
70
what determines the optimal wavelength for a given visual pigment
type of opsin
71
what is the same for all rhodopsins
11 cist retinal
72
trichromats
have 3 differenet opsins found in cones
| -different, but overlapping absorption spectra
73
rods have
same opsin and same absorption spectra
74
gene for rod opsin
3rd chromosome
75
gene for blue pigment opsin
7th chromosome
76
green and red pigment opsin
X chromosome
77
propanopia
red color blind
78
deuteranopia
green color blind
79
tritanipia
blue color blind
80
2 types of ganglion cells
M cells
| P cells
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M cells
mgnocellular- large receptive fields
| movement detection
82
p cells
parvocellular
smaller receptive fields
color vision
83
ganglion cells are
output cells of retina
| unlike photoreceptor cells, will fire AP when sufficiently depolarized
84
receptive field
specific area of retina that ganglion cells appears to be monitoring
85
3 features of the receptive field
roughly circular
center and surround
illumination of center is separate from illumination of surround
86
on center ganglion
stimulate center - activity inc, stimulate surround- act decreases
illuminate whole field- no difference because cancel out
87
off center ganglion
decrease in center
| increase in periphery
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W type gnaglion cells
do not have center surround organization adn respond to overall illumination of receptive field
89
w type ganglion cells contain
contain a photopigment called melanopsin--> act GPCR
sensitive to 480 (blue)
dusk and dawn-circadian rhythms
90
ganglion cells result in
enhanced contrast detection
| provide information about boundaries or edges of a stimulus
91
why does contrast start in the retina
slight differences could be distored or lost
much comparison between adjacent regions of the retina is done in the retina nad nearby regions sent to higher order brain by ganglion cells
92
retinitis pigmentoa
photoreceptor degeneration
| eventuall loss of vision effects 1.5 million people worldwide
93
macular degeneration
loss of pigment epithelium-->leads to photoreceptor loss
94
output from ganglion cells on
myelinated optic nerve
95
where do W type ganglion cells project
SCN of hypothalamus
96
projections to the superior colliclus
coordinates visual somatic and auditory to make 3 point to point maps or topographic represnetations of the visual, auditory, or somatic space
different aspecs of same point in space will all go to same point in colliclus
97
outputs frm superior colliclus
go to portions of midbrain controlling eyemovements, movements of head and neck, cerebellum for further coordination of eye and head movements
98
pupillary reflexes
w ganglion cells--Pretactal area-->edinger-westphal nucleus bilaterally-->oculomotor nerve-->ciliary ganglion-->control smooth muscles of pupillary sphincter
99
projections to lateral geniculat enucleus
most retinal projecions
sends them to regions of cortex involved in vision
topographic
100
6 layers of Lateral geniculate
3 from each eye
4 outermost- parvocellular layers-receive input from smaller P type ganglion cells- color vision/fine discrimination
inner 2- Magnocellular layers- m type-motion detection, depth, contrast NOT color
101
termination of photoreceptor response
activated inr esponse to decreased cGMP -->rhodopsin kinase phos rhodopsin-->retinal dissociates from opsin-->trans retinal-->all trans retinol (vit a)-->11cis transported to pigment epithelium by retinal binding protein
102
vit a deficiency
night blindness
103
guanylate cyclase
inhibited by Ca
| incrases cGMP
104
on center center
inc glut-->stimulated GPCR-->hyperpol-->decrease NT-->excite bp cell-->realse NT-->stimulate gang
105
on center surround
decrease glut-->depol photoR in center-->release NT on to bipolar-->inhibit
106
off center center
increase glut-->stimulate NMDA-->depol-->increase NT-->excit bp-->release NT-->stim
