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neuroscience > retinal phototransduction and signal processing > Flashcards

retinal phototransduction and signal processing Flashcards

1
Q

what structure of the eye focuses far objects?

A

the cornea

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2
Q

what structure of the eye focuses near objects?

A

the lens

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3
Q

What structure of the eye converts light energy into electrical signal?

A

the retina

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4
Q

what structure of the eye provides nourishes the cones and rods?

A

the choroid

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5
Q

through what structure of the eye does light enter?

A

the cornea

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6
Q

what structure of the eye is the site of the highest spatial acuity?

A

the fovea

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7
Q

where do the axons converge to exit the eye?

A

the optic disk

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8
Q

what causes cataracts?

A

aggregates of protein that form in the lens

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9
Q

what do cataracts do to your vision?

A

cause clouding of the lens ( cloudy vision) and results in a glare especially at night
faded colors

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10
Q

what are risk factors for cataracts?

A

aging, diabetes, sunlight, smoking

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11
Q

what is presbyopia?

A

inability to focus on near objects

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12
Q

what is hyperopia?

A

farsightedness

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13
Q

glaucoma causes?

A

optic nerve damage and irreversible loss of peripheral visual fields and ultimately vision loss

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14
Q

what are the types of glaucoma?

A

normal tension
open angle
closed angle

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15
Q

what is open angle glaucoma?

A

progressive ( occurring over time) caused by obstruction of drainage of the aqueous humor which puts stress on the retina

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16
Q

what is closed angle glaucoma?

A

caused by a collapsed wall leading to a closed or narrow angle between the iris and cornea. this results in an acute increase in intraocular pressure and requires immediate care/surgery

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17
Q

where does intracular pressure increase?

A

in the front of the eye

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18
Q

what are the risk factors for glaucoma?

A

elevated eye pressure, thin cornea, abnormal optic anatomy, high blood pressure

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19
Q

what is the treatment for glaucoma?

A

eye drops to decrease the aqueous drainage production or keep it from increasing, or surgery

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20
Q

what does the retina do?

A

contains neurons that absorb light and process visual information in the images and send that information to the brain.

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21
Q

where do photoreceptors point?

A

toward the back of the eye

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22
Q

What are the 5 types of neurons found in the retina?

A 
photoreceptors
horizontal cells
bipolar cells
amacrine cells
ganglionic cells
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23
Q

describe the flow of vertical information in the retina

A

info flows from photoreceptors to the bipolar cells to the ganglion cells and the cells release glutamate

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24
Q

describe the lateral flow of information in the retina

A

it is mediated by horizontal cells and amacrine cells and these cells release glycine or GABA

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25
Q

does a rod bipolar cell or a cone bipolar cell make 1 to 1 connections with cones?

A

rod bipolar cells contact cones 1 to 1

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26
Q

does a cone bipolar cell or a rod bipolar cell make several contacts with cones?

A

a cone bipolar cell makes several contacts with cones

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27
Q

where in the retina does phototransduction occur?

A

in the cilium aka the outer segment

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28
Q

what is in the inner segment of the retina?

A

nucleus, mitochondria, golgi, ER etc

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29
Q

what are the two types of photoreceptors?

A

rods and cones

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30
Q

how does the membrane potential of photoreceptors compare to that of most other neuron membrane potentials?

A

it is relatively depolarized rather than hyperpolarized at the resting potential ( near -40 mv)

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31
Q

what is graded hyperpolarization?

A

the way in which photoreceptors respond to light i.e. the more they are exposed intense light the more they HYPERPOLARIZE ( thus they DON”T form action potentials

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32
Q

IN dark light what is the [ cGMP] and how does that effect ionic influx/efflux and membrane potential?

A

in the dark there is an increase in [cGMP] which leads to an influx of Ca2+ and Na+ and an efflux of K+ leading to depolarization

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33
Q

IN dark light what is the [ cGMP] and how does that effect ionic influx/efflux and membrane potential?

A

in the light there is an decrease in [cGMP] which leads to an efflux of Ca2+ and Na+ and an influx of K+ leading to hyperpolarization

34
Q

Why is it that the phototransduction cascade provides high amplification of a single photon?

A

because 1 rhodopsin closes 200 cGMP channels which leads to a significant glutamate and a hyperpolarization

35
Q

what is rhodopsin?

A

g coupled receptor that is the primary light detector . it is a visual pigment protein that contains light absorbing chromophore 1-cis retinal ( an aldehyde of vitamin A)

36
Q

how does light absorption change the retinal?

A

it changes the conformation from 11-cis to all-trans

37
Q

what is dark adaptation?

A

when your eyes adapt to see in the dim light ( like in the movies)

38
Q

what happens to retinal during dark adaptation?

A

the retinal is restored from a all-trans conformation to an 11-cis conformation ( this is called the visual or retinoid cycle.) and it is transported back out to the outer segment of the retina to recombine with opsin and form pigment.

39
Q

what type of photoreceptor is found in great density in the periphery?

A

rods

40
Q

what type of photo receptor is found in great density in the center of the eye ( the fovea) ?

A

cones ( lots of Cones in the Center)

41
Q

where is there high spatial acuity in the eye and why?

A

in the fovea there is high spatial acuity and ( high resolution and low sensitivity) because there are lots of cones

42
Q

where in the eye is there low resolution and high sensitivity?

A

in the periphery because there are more rods than cones

43
Q

what is pushed aside in the fovea ganglion cells to allow for higher acuity?

A

the inner plexiform layer and the inner nuclear layer ( see pg 372 top left)

44
Q

1 cone —> 1 cone bipolar cell ( _________ bipolar cell)

A

midget

45
Q

what is scotopic vision?

A

rod- only vision: high sensitivity, low acuity, no color

46
Q

what is photopic vision?

A

(cone only vision) low sensitivity, high acuity, color

47
Q

what is mesopic vision?

A

cone and rod vision are active together

48
Q

What is retinitis pigments?

A

a genetic eye disease that leads to night blindness. tunnel vision and legal blindness usu by age 40.

no treatment is available.

49
Q

what is the cause for retinas pigments?

A

a mutation of genes for rhodopsin and other rod proteins lead to the degeneration of rods and eventually cones.

50
Q

what is an electrortinogram?

A

it is a brief change in potential evoked by a large field flaw of light to the eye recorded with a contact lenses electrode

it provides a measure of retinal function

51
Q

what is the leading cause of vision loss?

A

age-related macular degeneration

52
Q

what disease is caused by abnormal blood vessels behind the retina growing under the macula, leaking and rapidly damaging the retina?

A

wet age related macular degeneration

53
Q

what is the more common form of age related macular degeneration?

A

dry age related macular degeneration

54
Q

what symptoms are associated w/ in macular degeneration?

A

loss of central vision

55
Q

which photoreceptors are affect din macular degeneration?

A

there is a loss of cones

56
Q

what disease is caused when yellow deposits accumulate ( drunsen)

A

dry age related macular degeneration

the RPE and photoreceptors of the macula degenerate

57
Q

what are the symptoms of diabetic retinopathy?

A

blocked vision,: blurry vision with macular edema

58
Q

what are the two ties of diabetic retinopathy?

A

NON-PROLIFERATIVE (hyperglycemia- induced pericyte death–> incompetence of vascular walls–> microaneursyms and dot and blot hemorrhages and PROLIFERATIVE ( new vessels grow whig leak blood)

59
Q

which photoreceptors are affected in diabetic retinopathy?

A

none

60
Q

what is the area of the retina that when stimulated elicits a change in the response in a neuron?

A

the receptive field

61
Q

what is excitatory in the center and inhibitory in the surroundings?

A

the on center of the retina receptive field ( see pg 380)

62
Q

what is inhibitory in the center and excitatory in the surroundings?

A

the off center of the retina receptive field ( see pg 380)

63
Q

on center cells increase their dischargee rate to luminance __________ in the receptive field center

A

increments

64
Q

off center cells increase their dischargee rate to luminance __________ in the receptive field center

A

decrements

65
Q

why is it that when two different shades a darker and lighter are lined up next to each other there are differences in illumination ) edges)? ***

A

see page 381

66
Q

where is the contrast between light and dark “first decided”?

A

the first synapse i.e. the synapse between the photoreceptor and the bipolar cell .

therefore the cones and rods don’t know what light is on or off because it is the first synapse that determines this

67
Q

do on center bipolar cells depolarize or hyperpolarize in response to light?

A

they depolarize in response to light and hyper polarize in response to dark.

the off center bipolar cells do the opposite.

68
Q

how many bipolars cells does each cone connect to?

A

two an on and an off bipolar cell

69
Q

how many cones does each bipolar cell connect to?

A

one

70
Q

which synapse is inverting?

A

the synapse between the on center bipolar cell and the photoreceptor
( closes the channel)

71
Q

which synapses are non- inverting?

A
  1. btw the off center bipolar cell and the photoreceptor ( opens the channel )
  2. btw the off center bipolar cell and the off center ganglion cell
  3. btw the on center bipolar cell and the on center ganglion

these all use AMPA or NMDA

72
Q

trichromatic facilitates distinguishing btw ?

A

red and green

73
Q

color facilitates detecting?

A

borders btw objects

74
Q

which cells antagonize bipolar cell response to light?

A

horizontal cells and amacrine cells

75
Q

what is lateral inhibition?

A

inhibition that spreads from surround to center

76
Q

dichromatic means you can differentiate between?

A

btw blue and green

77
Q

what are the 3 cone types?

A

short (blue wavelength), medium (green wavelength), long ( red wavelength)

78
Q

what causes colorblindness?

A

changes in the number of red and green cone opsins.

79
Q

does each person have the same distribution of cones?

A

no but we have ability to detect differences in red and green

80
Q

which ganglion cells tell the difference between blue and yellow?

A

koniocellular cells

81
Q

which ganglion cells tell the difference between red and green?

A

parvocellular cells ( midget cells)

82
Q

what do intrinsic photosensitive retinal ganglion cells do?

A

they exhibit pupillary control and they are involved in synchronization of circadian rhythms

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