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Neuro > Vision > Flashcards

Vision Flashcards

0
Q

light collection

A

light in environment is collected and focused by the eye on photoreceptors

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1
Q

4 stages of visual perception

A

1) light collection- eye
2) transduction- retina
3) neural processing- retina
4) neural processing- visual cortex

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2
Q

transduction

A

light entering eye is converted into an electrical signal (transduction) by a specialized set of retinal neurons called photoreceptors

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3
Q

neural processing-retina

A

information is extracted from the electrical signals before it then sent through optic nerve to the lateral geniculate nucleus of brain

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4
Q

neural processing- visual cortex

A

additional information is extracted from image in a variety of cortical areas

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5
Q

compound eye

A

large number of collectors funnel the light onto sheet of receptors in insects
–advantage: motion detection, operates over a wide range of wavelengths, sensitive to polarized light

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6
Q

refractive eye

A

image is formed on retina by refraction through lenses

vertebrates–>resolving power

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7
Q

how can you increase resolution of compound eye?

A

increasing the number ommatidia (number of cells)

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8
Q

3 layers of eye

A

outer layer
choroid layer
retina

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9
Q

outer layer

A

sclera– outer white layer surrounding most of eye ball; shape and support
cornea- major refractive element of eye

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10
Q

limbus

A

junction of cornea and sclera

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11
Q

choroid layer

A

pigment epithelium & blood vessels supply oxygen and nutrients to retinal cells
iris- controlling diameter of pupil

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12
Q

retina

A

contains photoreceptors

–responsible for the initial detection and processing of light stimuli

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13
Q

cornea

A

cornea–most refractory/focusing power

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14
Q

anterior chamber is filled with

A

aqueous humor

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15
Q

what produces aqueous humor?

A

ciliary epithelium

at a rate of 2 microliters/minute, enough to replace all of the aqueous humor 10-20 times perday

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16
Q

where does aqueous go after anterior chamber

A

venous circulation via trabecular meshwork in the canal of schlemm

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17
Q

if canal of schlemm gets blocked…

A

fluid build up and increased pressure in eye

  • > pressure can build up enough to impede blood flow to optic nerve and retina –>blindness
  • *one of causes of glaucoma
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18
Q

glaucoma is associated with

A

optic nerve damage and loss of peripheral vision

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19
Q

size of pupil is controlled by

A

smooth muscles in iris–circular sphincter muscle fibers and the radially-organized dilator muscle fibers

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20
Q

changes in diameter of pupil change the

A

amount of light entering the eye

–depth of field

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21
Q

when pupil is constricted

A

depth of field increases

less light goes through

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22
Q

lens is the..

A

refractive element of eye

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23
Q

accomodation

A

changing the refractive power of the lens

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24
Q

ciliary muscles

A

shape of the lens is controlled by the amount of tension on it
(tension- wants to flatten, elasticity- wants to keep it rounded)
controlled by PS nervous system

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25
Q

when ciliary muscles contract

A

decreases tension on lens and lens gets more spherical

–>near vision, most refractive power

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26
Q

for viewing distant objects

A

muscles relax, lens is stretched so it is even flatter and thinner, least refractive index

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27
Q

by age 60

A

usually no lens accomodation left

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28
Q

myopia

A

eyeball too elongated, cornea too curved

focal plane is in front of retina–>near sighted

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29
Q

hyperopia

A

focal plane falls behind retina (not enough refractive power)
eye ball is flattened—>hyperopia

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30
Q

cancave lenses

A

subtract refractive power

–used for myopia

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31
Q

convex lenses

A

add refractive power

–used for hyperopia

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32
Q

cataracts

A

lens gets opaque in spots and interferes with vision

lens is made up of lens fibers–long, thin cells are filled with long, fibrous water soluble proteins–>crystallins

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33
Q

when the light goes through the retina

A

absorbed by photoreceptors OR passes through and hits pigmented epithelium lining back of eye

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34
Q

pigmented epithelium

A

composed of cells packed with black pigment melanin, which absorbs any light not captured by retina

  • -prevents the light from being reflected from teh back of the eye into the retina and distorting the image
  • -also plays a role in recycling of the photosensitive visual pigments and int he phagocytosis of the photoreceptor tips
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35
Q

part of retina where light is usually focused

A

fovea (small indentation of retina)-greatest visual acuity

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36
Q

why does fovea have greatest visual acuity

A

cone photoreceptors (better resolution than rods) predominate here

photoreceptors are closely packed there (density is highest there)

other neuronal cells of retina are pulled to the side, so ight doesnt have to go through them, resulting in less distortion

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37
Q

blind spot

A

small round area of retina that has no photoreceptors

–where the ganglion cells group together adn leave the eye (forming optic nerve)–>called optic disk

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38
Q

tapetum

A

nocturnal animals
behind retina that contains GUANINE crystals and is highly reflective–reflects light back through retina and provides photoreceptors with a “secnd change” to capture it
–>therefore, increases SENSITIVITY of eye to light and enhances night vision, but DECREASEs acuity

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39
Q

retinal detachment

A

junction between pigmented epithelium and photoreceptor layer is a weak point
–>problematic because photoreceptors not in the right focal plane and because tehy are not near their source of blood supply and nourishment

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40
Q

development of eye

A

optic stalk invaginates to form optic cup–>out layer becomes pigmented epithelium and inner layer becomes neural retina

ectoderm invaginates and forms LENS Vescile–>lens

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41
Q

macular degeneration

A

loss of pigment epithelium cells and eventually photoreceptors- wet and dry form

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42
Q

macular degeneration wet

A

involves tissue degradation and abnormal blood vessel growth

43
Q

dry

A

involves deposition of yellowish protein and lipid aggregates called “drusen”

44
Q

retina and photoreceptors are part of the ..

A

CNS

45
Q

retina and neurons derived from

A

neural ectoderm

46
Q

5 major classes of neurons in retina

A 
photoreceptor cells
bipolar cells
horizontal cells
amacrine cells
ganglion cells
47
Q

light getting to photoreceptors

A

light coming in travels through ALL cells before hitting photoreceptors
–unmyelinated layers, so they do not interfere or scatter to distort the image

48
Q

in the fovea, non-photoreceptor elements

A

shifted to the side so that the light has a more direct pathway to the receptor cells
–>less distortion and increased acuity in the foveal region

49
Q

two types of photoreceptor cells

A

rods

cones

50
Q

both rods and cones consist of

A

synaptic terminal
inner segment (nucleus & most of cellular synthetic machinery)
outer segment

51
Q

outsegment is connected to inner segment via

A

thin stialk/cilium that contains microtubules

  • ->filled with membranous disks that contain photopigments
    rods: disks pinch off and become free floating
    cones: remain connected to plasma membrane
52
Q

rod + disks

A

each segment contains 1000 disks and disk membranes contain photopigments (100 million)

53
Q

photoreceptors do not

A

divide, however they constantly renew at a rate of ~3 disks/hour

54
Q

phagocytosis of photoreceptor disks

A

at very tip, pigment epithelium cells phagocytotic activity removes discarded tips

55
Q

characteristics of rods

A

more sensitive than cones in detecting light

mediate night vision

56
Q

why are rods more sensitive than cones in detecting light?

A

have more photopigment and are longer, therefore are better at capturing light

amplify light signals more than cones– fewer photons needed to saturate response of rods

large amount of convergence with rods–many rods converge on a given bipolar cell in the retina–increases sensitivity with loss of resolution

57
Q

4 characteristics of cones

A

mediate day vision
better temporal resolution
better spatial resolution
color vision

58
Q

cones are more sensitive to

A

direct axial rays of light

59
Q

rods are more sensitive to

A

diffuse scattered light

60
Q

better resolution with cones beacuse

A

less convergence in cones system

61
Q

human eye is sensitive to wavelengths..

A

between 400 and 750 nm

blue–>green–>red

62
Q

where are the cones located

A

the fovea (no rods there(

63
Q

in reponse to light, photoreceptors

A

hyperpolarize

64
Q

in the dark..

A

incrase in cGMP–>more cGMP gated cation channels in outer seg open–>increase in Na, ca into cell–>depol–>inc NT release

65
Q

in teh light

A

decrease in cGMP–>more cation channels closed–>decrease Na, Ca into cell–>hyperpolarization–>decrease NT release

66
Q

to get to hydrolyze cGMP

A

rhodopsin binds transducin–>releases GDP, uptakes GTP by a subunit–>activates phosphodiesterase–>hydrolyzes cGMP

67
Q

adaptation

A

feedback mechanism where Ca inhibits guanylate cyclase

68
Q

in response to sustained level of intense illumination

A

all cation channels are shut down

cell hyperpolarizes to almost eq potential for K

69
Q

to change set point, you can change

A

rate of synthesis of guanylate cyclase

70
Q

what determines the optimal wavelength for a given visual pigment

A

type of opsin

71
Q

what is the same for all rhodopsins

A

11 cist retinal

72
Q

trichromats

A

have 3 differenet opsins found in cones

-different, but overlapping absorption spectra

73
Q

rods have

A

same opsin and same absorption spectra

74
Q

gene for rod opsin

A

3rd chromosome

75
Q

gene for blue pigment opsin

A

7th chromosome

76
Q

green and red pigment opsin

A

X chromosome

77
Q

propanopia

A

red color blind

78
Q

deuteranopia

A

green color blind

79
Q

tritanipia

A

blue color blind

80
Q

2 types of ganglion cells

A

M cells

P cells

81
Q

M cells

A

mgnocellular- large receptive fields

movement detection

82
Q

p cells

A

parvocellular
smaller receptive fields
color vision

83
Q

ganglion cells are

A

output cells of retina

unlike photoreceptor cells, will fire AP when sufficiently depolarized

84
Q

receptive field

A

specific area of retina that ganglion cells appears to be monitoring

85
Q

3 features of the receptive field

A

roughly circular
center and surround
illumination of center is separate from illumination of surround

86
Q

on center ganglion

A

stimulate center - activity inc, stimulate surround- act decreases
illuminate whole field- no difference because cancel out

87
Q

off center ganglion

A

decrease in center

increase in periphery

88
Q

W type gnaglion cells

A

do not have center surround organization adn respond to overall illumination of receptive field

89
Q

w type ganglion cells contain

A

contain a photopigment called melanopsin–> act GPCR
sensitive to 480 (blue)
dusk and dawn-circadian rhythms

90
Q

ganglion cells result in

A

enhanced contrast detection

provide information about boundaries or edges of a stimulus

91
Q

why does contrast start in the retina

A

slight differences could be distored or lost
much comparison between adjacent regions of the retina is done in the retina nad nearby regions sent to higher order brain by ganglion cells

92
Q

retinitis pigmentoa

A

photoreceptor degeneration

eventuall loss of vision effects 1.5 million people worldwide

93
Q

macular degeneration

A

loss of pigment epithelium–>leads to photoreceptor loss

94
Q

output from ganglion cells on

A

myelinated optic nerve

95
Q

where do W type ganglion cells project

A

SCN of hypothalamus

96
Q

projections to the superior colliclus

A

coordinates visual somatic and auditory to make 3 point to point maps or topographic represnetations of the visual, auditory, or somatic space

different aspecs of same point in space will all go to same point in colliclus

97
Q

outputs frm superior colliclus

A

go to portions of midbrain controlling eyemovements, movements of head and neck, cerebellum for further coordination of eye and head movements

98
Q

pupillary reflexes

A

w ganglion cells–Pretactal area–>edinger-westphal nucleus bilaterally–>oculomotor nerve–>ciliary ganglion–>control smooth muscles of pupillary sphincter

99
Q

projections to lateral geniculat enucleus

A

most retinal projecions
sends them to regions of cortex involved in vision
topographic

100
Q

6 layers of Lateral geniculate

A

3 from each eye

4 outermost- parvocellular layers-receive input from smaller P type ganglion cells- color vision/fine discrimination

inner 2- Magnocellular layers- m type-motion detection, depth, contrast NOT color

101
Q

termination of photoreceptor response

A

activated inr esponse to decreased cGMP –>rhodopsin kinase phos rhodopsin–>retinal dissociates from opsin–>trans retinal–>all trans retinol (vit a)–>11cis transported to pigment epithelium by retinal binding protein

102
Q

vit a deficiency

A

night blindness

103
Q

guanylate cyclase

A

inhibited by Ca

incrases cGMP

104
Q

on center center

A

inc glut–>stimulated GPCR–>hyperpol–>decrease NT–>excite bp cell–>realse NT–>stimulate gang

105
Q

on center surround

A

decrease glut–>depol photoR in center–>release NT on to bipolar–>inhibit

106
Q

off center center

A

increase glut–>stimulate NMDA–>depol–>increase NT–>excit bp–>release NT–>stim

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