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PHGY 209 > CNS/sensory 4 - visual > Flashcards

CNS/sensory 4 - visual Flashcards

1
Q

visual perception is dependent on…

A

context
bottom up modification

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1
Q

what is vitreous humour

A

clear jelly

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2
Q

what is retina

A

where transduction occurs

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3
Q

what is retinal pigment epithelium

A

layer of tissue
biochemistry of photoreceptors

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4
Q

what is optic nerve

A

axons of neurons in retina
sending visual info to brai

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5
Q

what is lens

A

can change shape

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6
Q

what is iris

A

changes size of pupil by constricting or dilating

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7
Q

what is pupil

A

behind cornea
can change size
Depends on light levels

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8
Q

what is cornea

A

part of eye
outer clear layer

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9
Q

what is sclera

A

white
becomes transparent in front = cornea

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10
Q

describe blood vessels of eye

A

part blocks photons

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11
Q

what is fovea centralis

A

highest visual acuity
like reading

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12
Q

what is optic disk

A

medial to fovea
blind spot - no photoreceptors here
brain fills it in

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13
Q

what does lens do

A

refracts
bends light to single point

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14
Q

describe how lens refracts light

A

happens when light travels to 2 diff substances
depends on angle of incidence of light and properties of substances
eye collects photons and refracts them - bend in a way where they occur at a single point on retina = focusing

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15
Q

what is light refracted by

A

cornea and lens

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16
Q

which refracts more light - cornea or lens

A

cornea refracts more light
image on retina is inverted
lens = flexible and controlled by some muscles that control its shape

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17
Q

describe accommodation for near vision

A

limited focal range - like if looking at something in distance = lens assumes a shape to focus on retina
if out of focus = ciliary muscles control lens shape
lens accommodates for changes in object location by changing shape

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18
Q

describe nearsightedness

A

eyeball too long
eye is myopic
image created in front of retina
can see objects up close fine but distance = hard
solution = squish eyeball or use corrective lens to compensate for too much refraction and focuses image on retina

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19
Q

describe farsightedness

A

eyeball too short
eye is hyperopic
pull eyeball longer or use lens

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20
Q

describe astigmatism

A

the lens or cornea are not spherical and smooth

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21
Q

describe presbyopia

A

lens gets stiff and is unable to accomodate for near vision
forms of farsightedness that happen after 45 = reading glasses

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22
Q

describe cataract

A

change in lens colour = becomes opaque and blocks photons entering eye

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23
Q

describe basic parts of organization of the retina

A

retinal pigment epithelium (cells interact with photoreceptors)–> transduction (rods and cones) –> change in neurotransmitter release–> processing and convergence (bipolar cells, horizontal cells, amacrine cells)–> becomes optic nerve (vitreous humour and ganglion cells)

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24
Q

describe fovea centralis (organization of the retina)

A

retinal circuitry is shifted out of the way

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25
Q

describe rods and cones (organization of the retina)

A

2 types of photoreceptors (~100mil/each eye)
1 type of rods = tend to be everywhere else, mediate low light vision, ~5mil in each retina
cones = 3 types of cones, mediate colour vision, mostly in fovea, central vision, highest acuity, small rf, ~90 mil in each retina
transduction occurs in photoreceptors

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26
Q

describe bipolar cells, horizontal cells, amacrine cells (organization of the retina)

A

circuitry does processes and extracts certain features from visual input
converges - optic nerve carries only 1 million

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27
Q

describe ganglion cells (organization of the retina) - gen

A

many photoreceptors drive a few ganglion cells
rf= bigger -driven by many rods and less cones
fire aps
axons = optice nerve

28
Q

describe ganglion cells (organization of the retina) - details

A

in center of vision - highest acuity = ganglion cells driven by 1,2,3 or 4 cones, in fovea = small rf
in periphery = ganglion cells driven by hundred of rods, big rf

29
Q

describe light (organization of the retina)

A

light entering causes closing of ion channels and photoreceptors
changes neurotransmitter release from photoreceptors
circuitry of horizontal, bipolar and amacrine cells

30
Q

is retina part of cns

A

yes technically but also sends info to cns

31
Q

name 2 portions of photoreceptor and describe

A

outer segment = stacked full of membrane disks = lipid membrane stacked,
inner segment = has nucleus - where neurotransmitter released

32
Q

describe phototransduction while in dark

A

outer segment = lots of cyclic GMP in intracellular space of photoreceptor and lining outer segment = cyclic gmp gated sodium channels (if channels open and photoreceptor depolarizes = neurotransmitter released into circuitry in dark when no photons)
photoreceptors releasing neurotransmitters all the time

33
Q

name 4 main steps of photo being released - transduction

A

light activates opsin molecule
g protein cascade
cGMP–>GMP
channels close

34
Q

describe chromophore (phototransduction)

A

retinene - inside disk, related to vit a
molecule that sits in protein called opsin (captures photons)

35
Q

describe specifically what happens during phototransduction

A

many disks stacked since photons hard to capture
since photon has billions of opsin proteins
rhodopsin - for rods
photons captured by opsin protein that contains chromophore
photon hits opsin molecule and chromophore and opsin separate and causes conformational change in opsin molecule = triggers g protein cascade
g protein cascade = motor, so triggers motor to start - can run for a while and converts cgmp to gmp
ion channels close - na channels close since less/no cgmp

36
Q

light causes receptors to…

A

Hyper polarize
transmitter released in dark usually, so photons cause reduction in neurotransmitter response

37
Q

how many different opsin molecules are there

A

4 diff opsin molecules
rhodopsin found in rods
(3 diff ones for 3 diff types of cones, sensitive to 3 different colours of light)

38
Q

what does middle circuitry do (phototransduction)

A

doing an inversion - causes reducrion in neurotransmitter to produce an increase drive of ganglion cells fire ap

39
Q

describe rods

A

high sensivity, night vision
more rhodopsin, captures more light
high amplification, single photon closes many na+ channels
slow response time - lasts longer and slower
more sensitivity to scattered light (animals = glowy eyes sine v reflective retinas, light reflected off retina so rods can capture scattered light)

40
Q

describe cones

A

low sensitivity, day vision
less opsin
lower amplification since many photons
faster response time
more sensitive to direct axial rays

41
Q

describe rod system

A

low acuity - not present in central fovea, highly convergent (many rods drive ganglion cels and rods)
achromatic = one type opsin

42
Q

describe cone system

A

high acuity = concentrated in fovea, less convergent, few cones drive ganglion cells
chromatic = three types of opsin

43
Q

describe dark adaptation

A

bright (rods are inactivated (opsin wiped out since hit with photons), cones are active) –> dark (temporary blindness until rods re-activate and take over, rods have to reconnect with chromophore, involves retinal pigment epithelium, 10-15 mins)

44
Q

describe light adaptation

A

dark (cones inactive, rods active) –> bright light (rods initially saturated, temporary blindness untill rods inactivate (opsin and chromophores will separate and cannot function) and cones take over)

45
Q

explain light and dark adaptation in more detail

A

once chromophore and opsin broken = cannot capture photons anymore
rods mediate light and dark adaptation
takes time to put the chromophore and opsin back together, slow process 10-15 mins

46
Q

what does retina report

A

relative intensity of light
depends on what around it
does not tell you exactly how many photons are there, just how many is there compared to surroundings
computation done by circuits

47
Q

what do ganglion cells of retina do

A

not same uniform thing
does computation compares middle of receptive field to center

48
Q

what do retinal ganglion cells have

A

center surround receptive fields

49
Q

name 2 types of ganglion cells

A

inhibitory surround and excitatory center
excitatory surround and inhibitory center

50
Q

what do retinal ganglion cells signal

A

relative differences of the light - contrast across receptive fields

51
Q

describe inhibitory surround and excitatory center ganglion cell response to lights

A

bright center dark surround = many aps in center
dark center bright surround = no aps in center
uniform light = same aps

52
Q

describe inhibitory center and excitatory surround ganglion cell response to lights

A

bright center dark surround = no aps in center
dark center bright surround = many aps in center
uniform light = same aps

53
Q

what are photoreceptors sensitive to

A

wavelength
blue, green, red
opsin molecule determine chromatic sensitivity of the photoreceptor
ganglion cells send info about dark and light and also sends info about colour, depends on which photoreceptors are converging

54
Q

what is perception of colour dependent on

A

context dependent

55
Q

what do retinal ganglion cells have - for colour

A

colour opponent receptive fields

56
Q

describe colour opponent receptive fields

A

green vs red and yellow vs purple
output of retina encodes values of brightness and colour
colour in middle vs surround

57
Q

describe colour blindness

A

more than 5% of population has deficit in colour perception
some opsins not functioning properly
could be due to genetics = perception of colour is different
mostly in males
could also be caused by damage or diseases and stuff

58
Q

describe flow of visual info in brain

A

left visual field
right visual field
temporal retina and nasal retina - temporal retina does not cross
axons coming from retinal ganglion cells that are receiving inputs = do cross midline at optic chiasm
optic nerve = one eye with both visual fields
cross at optic chiasm
optic tract = both eyes with contralateral visual field –> lateral geniculate nucleus (thalamus) synapses –> optic radiations towards back of brain –> visual cortext in occipital lobe - both eyes with contralateral visual field

59
Q

lesion in left optic nerve

A

loss of vision in ipsilateral eye

60
Q

lesion in optic chiasm

A

bilateral loss of temporal visual fields

61
Q

lesion in left optic tract

A

loss of contralateral visual field

62
Q

lesion in left occipital lobe

A

loss of vision in contralateral visual field

63
Q

what does polymodal mean

A

visual and other sensory modalities combined

64
Q

describe parietal stream

A

where
spatial features and motion
large rfs

65
Q

describe primary visual cortex

A

small rfs
simple image features like oriented line segments
start to extract basic features which can be put together to make visual image
in occipital lobe

66
Q

describe temporal visual stream

A

what
large rfs
complex image features
selective to high level features
hands, places, buildings
jennifer aniston neuron

67
Q

describe object recognition

A

faces

68
Q

where does all parts of visual world come together

A

in frontal love

PHGY 209 (19 decks)

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