The Visual System Part One Flashcards
(110 cards)
1
Q
Image on the retina
A
Inverted and reversed
2
Q
Info from the upper visual space
A
Projected onto the lower retina
3
Q
Info from the lower visual space
A
Projects to the upper retina
4
Q
Right part of visual space
A
Projects to the left hemiretina in each eye and vice versa
5
Q
Do the VF overlap
A
Yes most of it does, the minor peripheral zones do not
6
Q
Outermost layer of the eye
A
Sclera
7
Q
What is the sclera continuous with
A
Dura mater
8
Q
How does the sclera continue posteriorly
A
As the sheath of the CN2
9
Q
What begins at the limbus
A
Cornea
10
Q
Vascularized middle layer
A
Choroid plexus (uvea)
11
Q
Where is the choroid
A
Between the sclera and the retina
12
Q
Pigment of the choroid
A
Densely pigmented
13
Q
What is the principal route through which blood vessels and nerves travel within the wall of the eye
A
Choroid
14
Q
What do choroid caps supply
A
Retinal photoreceptors
15
Q
What does choroidal pigment do
A
Absorbs light
16
Q
How does the choroid continue anteriorly
A
Dorms the bulk of the ciliary body
17
Q
What is the choroid similar to
A
Arachnoid mater
18
Q
What is the innermost layer of the eye
A
Retina
19
Q
What part of the retina lies adjacent to the choroid
A
RPE
20
Q
Where do the rods and cones point towards
A
The choroid, light must cross all layers of the retina to get to the photoreceptors
21
Q
What are the layers of the retina from most superficial to deep (choroid to vitreous)
A
- Epithelial layer
- Photoreceptor cell outer and inner segments
- Outer limiting membrane
- Outer nuclear layer
- Outer plexiform layer
- The inner nuclear layer
- Inner plexiform layer
- Ganglion cell layer
- Nerve fiber layer
- Inner limiting membrane
22
Q
Where are the nuclei of the photoreceptor cells
A
Outer nuclear layer
23
Q
Where are the synaptic connections of photoreceptors with other retinal cells
A
Outer plexiform layer
24
Q
Contains the somata of second order and some third order retinal cells
A
Inner nuclear layer
25
Another area of synaptic contact in the retina other than the outer plexiform layer
Inner plexiform layer
26
What part of retina contains the cell bodies of the ganglion cells
Ganglion cell layer
27
What layer of the retina is composed of the axons of the ganglion cells that converge at the optic disc to form the optic nerve
Nerve fiber layer
28
This layer of the retina consists of glial cell processes joined by tight junctions
Inner limiting membrane
29
This retinal layer is located between the nerve fiber layer and the vitreous
Inner limiting membrane
30
This layer is a single layer of polygonal, pigmented cells
Retinal pigment epithelium
31
How do the RPE cells support the photoreceptors
Metabolically
32
What are the two main roles of the RPE
Support the photoreceptors metabolically and they play a role in absorbing light
33
What direction do the rods and cones point
Towards the epithelial layer (and choroid)
34
Relative to the direction of light, how are the rods and cones positioned
Backwards
35
5mm diamter region in the center of the retina
Macula lutea
36
What kind of photoreceptors are in the macula
Both, but predominantly cones
37
What kind of photoreceptors are in the fovea
Cones ONLY
38
What is the central fovea specialized for
Vision of the highest acuity
39
What is different about the deep retinal layers in the foveal area?
They are pushed aside so that the cones are exposed. Light gets right to the cones
40
What receives inputs from individual foveal cones
Midget bipolar cells
41
What do the midget bipolar cells contact after receiving inputs from individual foveal cones
Individual midget ganglion cells, so that an anatomical basis for highly detailed foveal vision is maintained
1:1!!
42
smaller receptive field
Better VAs
43
The larger the receptive field
The harder it is to discern between 2 points, worse VA
44
What kind of photo receptors are in the optic disc
None. This is where the central axons of ganglion cells leave the eye to form the optic nerve
45
Where do the central axons of hte ganglion cells originate
At the border with the vitreous
46
What must the central axons of ganglion cells do before passing through the sclera
Traverse the retina
47
Where is the blind spot
Where the optic disc is
48
Why is there a blind spot where the optic disc is
Because there are no photoreceptors there
49
Are we aware of the blind spot at the optic nerve?
No, the nervous system simply fills it in. The other eye compensates in binocular vision
50
Where does the density of the cones decrease sharply
Outside the fovea
51
Where does the density of rods increase sharply
Outside the fovea, reaching a maximum use outside the macula
52
What portion of the rods and cones are responsible for photoreception
The outer portions
53
The process by which photons are detected and the information is transducer into an electrical signal
Photoreception
54
What connects the outer segment to the inner segment of the photoreceptor and what does it contain
The ciliary. It contains mitochondria
55
Where are the nucleus of the photoreceptor cells found
Outer nuclear layer
56
Where do the photoreceptor cells terminate?
Outer plexiform layer in an expansion that makes synaptic contacts with neurons
57
What is the synaptic expansion on the rod cells called
Spherule
58
What is the synaptic expansion on the cone cells called
Pedicle
59
What do the surface membranes of rods and cones outer segments contain
cGMP gated Na+ channels
60
When are cGMP concentrations high
In the dark
61
When are the Na channels open, allowing a current of Na+ ions to flow freely into the outer segment?
In the dark
62
When are rods and cones depoalrized?
In the dark
63
What do rods and cones release at a steady rate in the dark
Glutamate
64
What does light induce in photoreceptors
Hydrolysis of gCMP, causing cation channels to close, the membrane hyperpolarizes, and transmitter release declines
65
What are the G protein-coupled receptors of the rods and cones
Opsins (photopigments)
66
What is the ligand of the receptor opsin
11-cis retinal (vit A derivative)
67
What is the effect of light on the opsin and 11-cis retinal
It isomerizes 11-CIA retinal to all-trans retinal, which dissociates from opsin
68
What does isomerized retinal do
Causes a conformational change in the opsin-opsin (trans) activates transducin (G protein)-transducin activates phosphodiesterase E (enzyme that hydrolyzes cGMP)-cGMP concentration decreases-Na channels close-secretion of glutamate stops
69
When is 11-cis-retinal bound to opsins (rhodopsin)
Dark
70
When does 11 trans retinal release from opsin and react with transducin?
In light
71
How many types of opsins in cones
3
72
How many types of opsins in rods
1
73
What are the different cone opsins
- L (red)
- M (green)
- S (blue)
74
What is the absorption peak of each class of cones determined by
The kind of opsin a particular cone makes
75
What kind of retinal do each of the cone opsins bind
They all bind 11-cis-retinal
76
What is the basis of trichromatic color in humans
The 3 different cone opsins
77
Which is more sensitive to light, rods or cones?
Rods
78
What kind of light do rods respond to
Only up to about moonlight levels of light intensity
79
What is the reaction time of rods
Slow
80
What kind of specificity do the rods have?
Not very specific. Could take up to thousands of rods to generate signal
81
Cone sensitivity
They have a smaller outer segment and less visual pigment. This makes them less sensitive
82
What do cones require to function effectively
Greater level of illumination
83
There is considerably less ______ in cone pathways than in rod pathways
Convergence
84
What makes possible the huge resolution of fine spatial detail
There is less convergence in cone pathways than in rod pathways
85
Where is acuity highest
Where midget ganglion cells have receptive fields with centers the size of a single cone (1:1!!)
86
What kind of synapses can photoreceptor cells form with bipolar cells
Either excitatory or inhibitory
87
Is glutamate release all or nothing?
No, it is gradual and depends on the amount of light
88
Where do rod bipolar cells terminate
On processes of special amacrine cells, depolarizing them, and they in turn depolarize ganglion cells
89
Portion of the VF where light causes excitation or inhibition of one retinal ganglion cell
Receptive field
90
How are receptive fields determined
- Photoreceptors respond to light in their respective fields and form excitatory or inhibitory synapses onto bipolar cells
- bipolar cells, in turn, synapse onto ganglion cells, whihc send sons into the optic nerve
- convey info RBC releasing NT in a graded fashion
- ganglion cells fire APs as they convey info into optic nerve
91
Are receptive fields yes or no
Yes
92
Center surround receptive fields
- composed of roughly circular zones
- illumination of the central area causes an increase in firing rate, whereas illumination of the peripheral area has the opposite affect
- this is an On-center OFF-surround receptive field
- Off-center ON surround receptive fields also exist
93
What has to happen for he ganglion cells in a receptive field to be activate
Has to have at least part of the off or part of the ON deactivated. If they are all illuminated or all under dim conditions they will cancel each other out
94
Simultaneous illumination of both enter and surround causes what
Relatively little change in firing rate because the antagonistic effects of the two areas roughly cancel each other
95
Contrast between the two different areas of the receptive fields
At the level of the ganglion cells, the contrast between the two is of paramount importance
96
What is scotoma most often lay produced by
Lesions of the retina
97
What does a scotoma represent
A visual field defect, single or multiple
98
Likely causes of scotoma
Embolus, hemorrhage
99
Amaurosis fugax and scotoma
Treat by rubbing the eyebulb to dislodge the embolus or at least move it forward to decrease the lesion size
100
An inherited, degenerative disease that causes severe vision impairment due to the progressive degeneration of the rod photoreceptor cells in the retina
Retinitis pigmentosa
101
What is responsible for the majority of autosomal-dominant inherited retinitis pigmentosa cases
Mutations in the rhodopsin gene disrupts the rod-opsin protein
102
What is the temporal profile of retinitis pigmentosa
Insidious, progresses slow and steady
103
What is the give away for retinitis pigmentosa
Tunnel vision
104
Where are the genes for the red and green cone pigments
X chromosomes
105
What can cause a red green color blindness
Unequal crossing over during meiosis can cause one X chromosome to wind up with a missing or defective red or green gene
106
Lack of red pigment
Protanopia
107
Lack of green pigment
Deuteranopia
108
What percent of population is RGcolorblind
2% male population
109
Lack of blue cone pigment
Rare because located on chromosome 7, equally uncommon in males and females
110
Absence of red makes it difficult to see what colors
Red, yellow, and green objects
