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Neuroscience - sensory systems > Vision > Flashcards

Vision Flashcards

1
Q

where does the optic nerve terminate

A

LGN lateral geniculate nucleus ( a relay to the visual cortex)

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2
Q

what is the optic chiasm

A

left and right optic nerve cross at the chiasm, forming a characteristic X shape located in the forebrain directly in front of the hypothalamus

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3
Q

where are the nasal and temporal retinas

A

nasal (medial) retinas are on the inner half

temporal (lateral) retinas are on the outer halves

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4
Q

the right visual field is detected by ___________________________ and extends to the __________

A

detected by the left temporal retina and the right nasal retina -
extends to the left side of the brain

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5
Q

the left nasal retina and the right temporal retina take information from the _______________ and project to the _____________

A

take information form the left visual field and extend to the right side of the brain

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6
Q

the retinal ganglion cells sends information to which two nuclei

A

pretectal nucleus (reflexive eye movements) & suprachiasmatic nucleus (sleep – wake cycle)

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7
Q

what are the three layers of the eyeball

A

– Sclera (tough outer layer)
– Choroid (where blood vessels are)
– Retina (at the back)

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8
Q

what is the eyeball filled with

A

vitreous humour

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9
Q

what are the highly transparent structures of the eye

A

cornea and lens

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10
Q

where is highest resolution vision detected (high acuity)

A

in the fovea centralis

because it is densely saturated with cone photoreceptors

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11
Q

where is the blind spot and what causes it

A

where the optical nerve is – where your optic nerve connects to your retina has no light-sensitive cells, so you can’t see anything there

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12
Q

what structures refract the light.

A

– Cornea provides most of refraction
– Lens is adjustable => fixed by ligaments that allows for accommodation - changing your optical power to focus near and far, can flatten or rounden

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13
Q

_________ range decreases as you age

A

accommodation

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14
Q

what are optic gliomas

A

tumours that can grow within the chiasm or in conjunction with the hypothalamic tumours, they can directly affect optic nerves.
Can cause, buldging eyes or vision loss, squinting or involuntary eye movements, elevated intercranial pressure and loss of appetite/fat reduction

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15
Q

what are refractive errors

A

caused by irregularity in the size and shape of the eye. vision blurred/ hard to focus because the refracted light isnt focussed on the retina - refractive power doesnt match the length of your eyeball

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16
Q

what is emmentropia

A

The state of the eyes without refractive errors - your vision is normal at you can see clearly at all distances because a point at an infinite distance from the eye is conjugate to the retina.

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17
Q

give two examples of Ametropia (refractive errors)

A

myopia - near-sightedness, near objects seen clearly, far objects are blurry because refraction focuses images in front of your retina
hyperopia - far object clear, near object blurry because you eyeball is too short and the light is focussed behind your retina

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18
Q

what is hypertropia

A

a form of vertical strabismus where one eye is deviated upwards in comparison to the fellow eye. Refraction causes focus behind the retina

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19
Q

what developmental vesicle does the retina form from

A

the diencephalon (optic vesicle)

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20
Q

what are the 5 neuronal cells types found in the retina

A 
–	Photoreceptors
–	Bipolarcells
–	Ganglion cells
–	Amacrine cells (modulate)
–	Horizontal cells (modulate)
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21
Q

what are the layers of the retina

A 
inner plexiform layer
inner nuclear layer
outer plexiform layer
outer nuclear layer
rods and cones
pigmented epithelium
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22
Q

the left visual feild is projected to the ___________ lateral geniculate nucelus

A

contralateral

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23
Q

how much of our cortical area is made up of the visual cortex

A

40%

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24
Q

why is there overlap of the visual feilds

A

central part of visual feild (in front of you) is detected by both eyes (peripheral just detected by one)

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25
Q

which retinal ganglion cell axons cross into the contralateral hemisphere

A

those coming from the nasal part of the retina

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26
Q

where do the cell bodies of the photoreceptors sit

A

in the outer nuclear layer

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27
Q

where is the pigmented epithelium and why is is specialised in this way

A

(next to) inner to the photoreceptors

highly pigmented to prevent scatter of light allows us to get a sharper picture and supports the photoreceptors

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28
Q

which layer of the retina are the neuronal synapses of horizontal cells and photoreceptors

A

outer plexiform layer

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29
Q

where are bipolar cell bodies housed in the retina

A

inner nuclear layer

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30
Q

what is in the inner plexiform layer

A

synaptic connections between the axons of bipolar cells and dendrites of ganglion cells

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31
Q

what is the simplest circuit of neurons in the retina

A

photoreceptor -> bipolar cell -> ganglion cell

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32
Q

what is the order of cells from the surface facing the light to the photoreceptors

A

light -> ganglion cells -> amacrine -> bipolar -> horizontal -> rods + cones

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33
Q

what do photoreceptors detect

A

400-700nm of the electromagnetic spectrum

34
Q

where is the pigment for light detection located

A

in the disks of the outer segment of photoreceptors

35
Q

where is photopigment regenerated

A

in the retinal pigmented epithelium adjacent to the photoreceptors

36
Q

what clears away the shed disks

A

the retinal pigmented epithelium

37
Q

light detection leads to ___________

A

hyperpolarisation
closing of Na/Ca channels
(intense light big hyperpolarisation, low intensity light little hyperpolarisation)

38
Q

which cells work with graded responses and which with the classic action potentials

A

photoreceptors and bipolar cells have graded responses (hyperpolarisation)
ganglion cells have the classic action potential (depolarisation)

39
Q

what are the Na+/Ca++ channels gated by

A

cGMP

40
Q

what are the differences between rods and cones

A 
•	low spatial resolution
•	High sensitivity (1 photon)
•	don’t contribute much after 0.1luninacelogcd/m-2 (very good in the dark)
Cones:
•	High spatial resolution
•	Low sensitivity (>100 photons) (more suited to brighter environments)
•	Less saturation
•	Rapid recovery
mediate colour vision
41
Q

loss of rod function leads to

A

night blindness

42
Q

loss of cone function leads to…

A

legal blindness

43
Q

at what luminance do cones begin to contribute

A

about -4 logcd/m-2 (at about starlight)

44
Q

at what luminance do rods becomes saturated and stop contributing to vision

A

in between 0-1 log cd/m-2

45
Q

what colour are each of the short medium and long wavelength visible light

A 
short = blue
medium = green
long = red
46
Q

how do we detect colour

A

a combination/comparison of activity of difference classes of monochromatic cone cells detecting each of the short (blue) medium (green) and long (red) wavelengths of light

47
Q

why are males more likely to have different colour vision/ colour blindness

A

because the medium and long wavelength cones are on the X chromosome
(females have two so can correct)

48
Q

what happens when light is absorbed by photoreceptors

A

Upon light adsorption there is a conformational change in the cis to trans retinal that induces a conformation change in the opsin activating transducin, the alpha subunit of transducin dissociates bound to GTP and activates on phosphodiesterase molecule which degrades the cGMP to get GMP. This means the Na+/Ca++ channel closes causing hyperpolarisation.

49
Q

at what points in the molecular cascade is the signal ampliied

A

conformational change of opsin activates hundreds of transducins
PDE degradation of 6 cGMPs

  • a single photon can close around 200 channels change in -1mV
50
Q

how is the light signal terminated

A

intracellular calcium decrease -
=> guanylate cyclase activity increases (cGMP restored)
=> rhodopsin kinase gets activated, phosphorylates rhodopsin => arrestin binding/ transducin displacement
+ all trans retinol dissociates

51
Q

the biggest signal amplification upon light detection occurs at which stage

A

the stage of transducin activation

52
Q

what structure generate 11-cis retinal

A

the retinal pigmented epithelium

53
Q

what is the difference between the density of photoreceptors in the perifoveal and foveal zones

A

the fovea has a very high density of cones and no rods

as you go out to the periphery the cones drastically declines the rods also decline a bit

54
Q

what is visual resolution

A

the distance between two points that can be distinguished

55
Q

how does contract help with resolution

A

high contact is more easily resolved

square wave grating is more easily distinguished that sine wave grating

56
Q

most of the information we receive is encoded by _________ rather than

A

Most info we receive is encoded by light and dark rather than colour.
(we don’t lose that much info in black and white movies)

57
Q

what cells axons form the optic nerve

A

the retinal ganglion cells

58
Q

what do ganglion cells detect

A

changes in luminance

59
Q

what are the two types of ganglion cells

A

on-center GC (a cells that fires when light hits the centre of the receptive feild)
and off-center GC (falls silent when centre is relatively brighter)

60
Q

what is the receptive feild

A

the region in which a stimulus elicits an AP

61
Q

what activity occurs in on centre ganglion cells

A

when light hits the centre it fires (relative to the outside)
when dark hits centre (outer is relatively brighter than centre) it switches off

62
Q

when does activity occur in off-centre ganglion cells

A

when the outer is relatively brighter to the inner

opposite to on centre ganglion cells

63
Q

what is lateral inhibition in ganglion cells

A

There is little or no response to a large (full field) spot of light that covers both the center and the surround because excitation in the center cancels the inhibition from the surround

64
Q

what receptors are associated with on centre ganglion cells

A

mGluR6

65
Q

what neurotransmitter receptors are associated with off centre ganglion cells

A

AMPA/ kainate receptors

66
Q

which type of ganglion cell is sign inverting and why

A

on centre ganglion cells - because hyperpolarisation causes them to depolarise in response to light detection in the cone

67
Q

what do horizontal cells do

A

sample a broad area of photoreceptors and connect s to other horizontal cells via gap junctions (fast signalling to other horizontal cells). together they allow detection over a large area of the retina (detection of background illumination)

68
Q
A

glutamate releases depolarises horizontal cells, releases gaba onto photoreceptor leading to hyperpolarisation (sign inverting) response to whole population over the retina

69
Q

how many rod cells are in the human retina

A

90 million

70
Q

how many cone cells are in the human retina

A

4.5 million

71
Q

which cells in the retinal circuit detect background illumination

A

horizontal cells

72
Q

ganglion cells in the optic tract project to

A

pretectum
suprachiasmatic nucleus (hypothalamus)
superior colliculus
dorsal lateral geniculate nucleus

73
Q

what does the pretectum do in response to light

A

feeds back to constrictor muscle in iris => pupillary light reflex

74
Q

what does the suprachiasmatic nucleus do in response to light

A

circadian (day – night) cycle

75
Q

what does the superior colliculus do in response to light

A

coordination of movement in response to visual cues

76
Q

retinotopic point to point projection is

A

the organisation of the projections from each eye that terminate in alternating layers

77
Q

spatial arrangement of the retina is maintain throughout the visual pathway however…

A

the visual pathway however not in proportion: peripheral field gets a smaller portion of the visual cortex, the macula a relatively small retinal area gets a large proportion of processing area in the cortex

78
Q

columns in the cortex respond to _________. adjacent columns respond to _________.

A

columns respond to one direction/orientation.

adjacent columns respond to progressive shifts

79
Q

which layer of the visual cortex do the lateral geniculate neurons terminate

A

in alternating ocular dominance columns in cortical layer 4

80
Q

what allows binocular vision

A

inputs from both eyes come together (outside layer 4, above and below) in the striate cortex, the relative strength of input varies, the centre of the column input from one eye and at the boundaries there is input from both ayes and everything in between

Neuroscience - sensory systems (4 decks)

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