vision B Flashcards

1
Q

how many photoreceptors are in the eye

A

130 mill

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2
Q

what signals do photoreceptors transform light, intensity, colour pattterns into

A

chemical and electrical signals that trigger activity of retinal cells

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3
Q

photoreceptors to ganglion cells

A

130 to 1

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4
Q

what do we use to see the retinal inner surface

A

clinical opthalmoscope

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5
Q

where is the optic disc located

A

nasaly

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6
Q

what is the optic disc

A

our blind spot

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7
Q

where isthe macula/ fovea located

A

temporally

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8
Q

what do rays not have to pass through

A

retinal pigment epithelium, choriocapilllaris, sclera to reach the epithelium

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9
Q

cones

A

colour specific and high acuity
concentrated in the fovea
end stage diferentiated and non proliferative

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10
Q

rods

A

no colour specificity and low acuity
high sensitivity
in the peripheral retina
end stage diferentiated and non proliferative

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11
Q

3 classes of cones

A

trichromat person has normal colour vision
s cones- short wavelength- blue and purple
m cones- middle wavelength- green
l cones- long wavelength- yellow and red

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12
Q

monochromats

A

totally colour blind with one cone pathway plus rod pathway

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13
Q

dichromats

A

a cone photopigment missing thus only has two cone channels

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14
Q

anomalous trichromats

A

all three cone photopigments with one photopigment anomalous in having a shifted peak sensitivity

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15
Q

where are the retinal photoreceptors located

A

anterior to retinal pigment epithelium and behind all other transparent neural retinal cell layers

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16
Q

retinal photoreceptors relationship with RPE - retinal pigment epithelium

A

have a close physical nad functional relationship

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17
Q

what do retinal photoreceptors convert

A

photonic energy to chemical signals by virtue of thier special cellular structure consisting of an inner cell body and an outer segment of photopigment

18
Q

photoreceptor renewal

A

stacks of discs of visual pigment molecules pf photoreceptors are constantly renewed with new discs added at the base of the outer segment displacing the old discs up the outer segment and pinched off at the tips and engulfed by retinal pigment epithelium on a diurmal cycle peaking in the morning

19
Q

rhodopsin in the dark

A

unstimulated, cgmp is available and binds to cation channels and those channels and kep t open by the cgmp wihch depolarizes the photoreceptor

20
Q

rhodopsin in light

A

stimulated starting a cascade involving transducin and phosphodiesterase PDE becomes more activated which then degrades cgmp. cgmp levels begin to decrease and cation channels begin to close and start to hyperpolarize the photoreceptor

21
Q

what sends impulses to the visual cortex

A

Bipolar cells and ganglion cells

22
Q

what does photoreceptor hyperpolarization lead to

A

decreased release of inhibitory neurotransitter such as glutamate onto downstream retinal neurons which leads to increased action potentials in these downstream neurons

23
Q

rod to ganglion cell connections

A

high convergence- less cell to cell connections

24
Q

cone to ganglion cell connections

A

low convergence- more cell to cell connections

25
Q

why is rods resolution low

A

bc of the way the wiring is done and rods have high convergence so lower resolution

26
Q

what do horizontal cells do

A

connect photoreceptors laterally and dampen cells surrounding the centre of maximal receptive stimulation. inhibit surrounding less stimulated cells and effect lateral inhibition

27
Q

cone cells are

A

receptive fields for GC

28
Q

ganglion cells serve

A

cone based receptive fields

29
Q

what are the two types of ganglion cells that cone photoreceptors synapse with

A

on and off centre ganglion cells

30
Q

on centre, off surround field

A

excites ganglion cell that response to on centre light
inhibit off centre ganglion cell

31
Q

off centre, on surround field

A

inhibits ganglion cell that responds to on centre light
exites off centre ganglion cell

32
Q

diffuse light on both centre and surround

A

weak response from both on and off centre ganlgion cells

33
Q

what kind of inhibition do peripheral cones do

A

compared to foveal cones their connect to more horizontal cells which further inhibit neighbouring cells getting weaker stimuli which optimizes acuity

34
Q

temporal and nasal axons crossing

A

temporal stay temporal and nasal cross at optic chiasm

35
Q

retinal pathology

A

showed by clinical opthalomoscope
retinopathy

36
Q

what is the macula

A

extension of the fovea

37
Q

optic disc location

A

nasal and fovea is temporal

38
Q

retinal pigment epithelium purpose

A

to take up the garbage made by the photoreceptors

39
Q

what do horizontal cells do

A

allow photoreceptor cells to modulate each other

40
Q

rhodopsin

A

a type of opsin