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sensory systems > colour vision > Flashcards

colour vision Flashcards

1
Q

visible light is part of which spectrum?

A

electromagnetic

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2
Q

what components make up visible light?

A

wave and particle

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3
Q

wavelength of visible light

A

400-750/800nm

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4
Q

what determines the colour of light?

A

frequency

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5
Q

3 retinal cones

A

red, green, blue

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6
Q

what is the basis of colour vision?

A

comparing between cones in two dimensions
ratio of activity across photoreceptors

comparing the activity of neighbouring cones with differing spectral sensitivity

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7
Q

what cones do we make comparisons between?

A

red vs green
yellow vs blue
yellow is a mixture of red and green

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8
Q

mechanism for red green comparison

A

colour opponent centre: surround
balance of inhibitory and excitatory input on the central cone

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9
Q

mechanism for blue: yellow comparison

A

colour opponent ON and OFF bipolars, were red and green synapse with the same bipolar cell

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10
Q

If blue is connected to on bipolar cell and yellow to off…

A

excited in blue light

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11
Q

If yellow is connected to on bipolar cell and blue to off…

A

most excited in yellow light

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12
Q

what type of polarisation occurs with colour vision

A

graded polarisation

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13
Q

opsin protein

A
  • 7 transmembrane domain G protein coupled receptor
  • Binds retinaldehyde
  • Translates isomerisation of retinal into a ‘biological’ signal
  • Determines spectral sensitivity
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14
Q

what is retinaldehyde most sensitive to when not bound to an opsin protein?

A

UV light

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15
Q

what happens to retinaldehyde when bound to an opsin protein? What causes this change?

A

its wavelength sensitivity shifts towards the visual light spectrum by adjusting its amino acid structure

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16
Q

long wave cone sensitivity and colour

A

564nm red

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17
Q

middle wave cone sensitivity and colour

A

533nm green

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18
Q

short wave cone sensitivity and colour

A

433nm blue

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19
Q

what determines the wavelength of light that retinaldehyde is most sensitive to?

A

the amino acid structure of the protein opsin

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20
Q

where are the characteristics of the protein opsin determined?

A

amino acid sequence encoded in our genome

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21
Q

why can our cone opsin proteins be different from one another?

A

we dont all have the same amino acid sequence surrounding retinaldehyde as each other, genetic differences

22
Q

in what ways may cone opsins not work equally well across individuals?

A

not enough wavelength sensitivity difference between your red and green cone opsins

one of your red or green opsins is malfunctional
In these cases you may loose ability to discriminate between red and green

23
Q

why do red-green discrimination errors occur more in males than females?

A

Human Long wavelength sensitive and melanopsin wavelength sensitive opsins are X linked (expressed on our X chromosome)

  • If gene on men’s X chromosome is faulty it will be expressed
24
Q

why is yellow, green colour discrimination less common in

A

not x linked

25
Q

what could adding cone types allow?

A
  1. Improved spectral resolution within human visible range
    1. Extend to UV
26
Q

how many cone opsins do most mammals have? what does this cause

A

two
red green colour blindness

27
Q

how many cone opsin receptors do chickens have?

A

four, they have an additional blue visual receptor

28
Q

why are mammals the worst at colour vision?

A

we only have photoreceptors in our eyes

most mammals only have 2 cone opsin genes

29
Q

inter-individual and species differences in cones:

A

number of cone classes
their spectral sensitivity

30
Q

sensory requirements causing differences in species vision capacity

A

nature of the environment they are living in

land or water

31
Q

ocean surface species have how many cone opsins

A

> 4

32
Q

what wavelength does water transmit more effectively than others?

A

blue

33
Q

what range of wavelengths do you get at very deep water

A

very narrow range, appears blue to us

34
Q

how many cone opsins do deep sea species have? what so these encode?

A

two, encoding ‘blue’ sensitive pigments

35
Q

why do almost all mammals have only 2 cone opsins

A

many mammals are nocturnal, so would have less use for cone opsins
at the same time in evolution would’ve lost photoreceptors in other parts of the body

36
Q

what are primates the only group to do?

A

re-evolve a 3rd cone opsin gene

37
Q

how many cone opsins did ancestral vertebrate have?

A

at least 4 cone opsins

38
Q

What determines species differences in vision capacity

A

sensory requirements (nature of environment they are living in

evolutionary history

39
Q

what cone opsin may people lack?

A

the green cone opsin

40
Q

what cone opsin is always x linked in mammals?

A

the green cone opsin/ long wavelength sensitive opsin

41
Q

how many and what cone opsins does a mouse have?

A

two cone opsins

green and UV sensitive

42
Q

how did new world monkeys develop trichromatic vision?

A

Stable polymorphism on the x chromosome involving two variants of cone opsin gene

same cone opsin gene, but with different amino acids which means it can shift between being sensitive mostly to green or red spectrum

43
Q

why are new world monkeys colourblind?

A

the polymorphism allele is X linked so they can only have one version of the allele

44
Q

what evidence suggests that trichromatic development in primates is under positive selection

A

it has developed multiple times in new world monkeys

45
Q

what is the advantage of having females with heterozygous alleles for cone opsins in new world monkeys?

A

females in the group may lead tasks using colour discrimination. E.g., food selection

46
Q

how did old world monkey’s develop trichromatic vision?

A

Duplication of the green cone opsin gene on X chromosome, so X chromosome

accumulation of mutations to shift its spectral sensitivity- so one’s spectral sensitivity is more red and one is more green

47
Q

do male or female old world monkeys have trichromatic vision?

A

both

48
Q

what is the advantage of red/green colour discrimination in primates?

A

important in discrimination of colour in fruit and vegetation

49
Q

what is needed for red green discrimination further than cone opsin genes

A

retina/brain capable of comparing their activation

50
Q

Engineer female mouse X chromosome green opsin to express human red opsin (result)

A
  • Wild type mice cannot distinguish red from green panel to claim reward
  • transgenic mice gradually learn to do this
51
Q

Engineer female mouse X chromosome green opsin to express human red opsin (conclusion)

A

Red-green discrimination arises from existing centre:surround organisation
All it requires is that the centre has an over representation of one cone class vs the surround

sensory systems (17 decks)

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