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PSL300 > Photoreceptors > Flashcards

Photoreceptors Flashcards

1
Q

where are the photoreceptors located?

A

in the retina

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2
Q

what is the conversion of light to electrical signals called?

A

phototransduction

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3
Q

What are the two main photoreceptors in the retina?

A

cones and rods

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4
Q

does our eye contain more cones or rods

A

rods

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5
Q

T/F. photoreceptors release action potentials?

A

false they respond to stimuli with graded membrane potentials

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6
Q

basic structure of cones and rods

A

their membrane folds into disk like layers which contain visual pigments

the inner segment contains the nucleus and organelles for protein synthesis

in the basal layer the synapse release glutamate

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7
Q

which direction do both cones and rods point to

A

the back of the eye

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8
Q

how do photoreceptors detect light

A

they use membrane bound visual pigments.

when light hits these pigments they change shape, causing a chemical cascade that hyperpolarizes the cell reducing glutamate release

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9
Q

why are photoreceptors more active in the dark?

A

because there is less light hitting the pigments, depolarizing the cells triggering more release of glutamate

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10
Q

why is glutamate release important in the eye?

A

because it helps transfer visual information

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11
Q

what is the pigment found in rods?

A

rhodopsin

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12
Q

how many pigments are in cones

A

3

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13
Q

how are photoreceptors distributed in the eye

A

not uniformly, instead they are packed in the macula a central disk and also packed tightly in the fovea

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14
Q

fovea

A

the fovea is used for detailed vision

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15
Q

are there photoreceptors in the blind spot?

A

no, this is where axons carrying visual information exit the eyeball to form the optic nerve

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16
Q

What type of light are cones used for?

A

bright light because they are less sensitive than rods

they distinguish colours but don’t operate in dim conditions

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17
Q

what type of light are rods used for?

A

dim light, in sunlight they are bleached out, meaning that their rhodopsin is broken down

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18
Q

does the fovea contain an even amount of cones and rods?

A

no fovea contains almost only cones

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19
Q

Where is the rod presence concentrated?

A

in the peripheral retina

20
Q

what are the three layers of neurons in the retina

A

photoreceptors synapse on the bipolar cells and those synapse on the ganglion cells

21
Q

where is convergence strongest in the eye? Where is it weakest?

A

strongest in the peripheral retina and weakest in the fovea

22
Q

receptive field

A

every neuron in the visual system has a receptive/visual field. which is the region of the retina where the light affects the cell’s activity- the set of photoreceptors which affect the cell

23
Q

what type of receptive field do bipolar cells have?

A

center-rounded fields with round center region and doughnut shaped surround

24
Q

what does it mean that bipolar cell receptive field can be on/off center

A

on center means the cells are excited by light in the center of field and inhibited by light in the surround.

off center means cells are inhibited by light in the center and excited by light in the surround

25
Q

what do on center cells respond the most to? off-center

A

on-center cells respond most when light fills their center and the surround is dark.

off center respond best when a dark spot fills their center and the surround light

26
Q

what do bipolar cells react the strongest to?

A

when there is a contrast in light

27
Q

Do bipolar cells fire action potentials?

A

no, they respond with graded membrane potentials

28
Q

what is the major difference between ganglion cells and bipolar cells and photoreceptors

A

ganglion cells can fire action potentials

29
Q

how are ganglion and bipolar cells similar

A

ganglion cells can also be off/on centred meaning it responds well to contrast

30
Q

what does this emphasis on contrast explain

A

the chevreul illusion where left right hand bands seem darker than the middle even though it is the same color throughout

31
Q

where are ganglion cells most sensitive

A

in the periphery but poor at reporting spatial detail

32
Q

where are ganglion cells less senstive

A

near the fovea but they have better spatial resolution

33
Q

Magnocellular ganglion cells

A

provide information that is used by brain to infer movement- 10% of ganglion cells are M cells

34
Q

Parvocellular ganglion cells

A

provide information that is used to infer form and fine detail like texture. 70% of ganglion cells are P cells

35
Q

melanopsin ganglion cells

A

these are photoreceptors that have their own visual pigment- melanopsin- they project to suprachiasmatic nucleus a center for circadian rhythms

36
Q

how does visual information move>

A

ganglion cells> retina> brain

37
Q

optic chiasm

A

the point where the visual information crosses to the other side.

Information from the nasal half of each retina cross the optic chiasm

38
Q

T/F. both nasal and temporal fibers cross the chiasm.

A

false only nasal fibers cross

39
Q

Why do fibers cross

A

because the right side projects to the left side and vise versa

40
Q

where does information move after crossing the chiasm?

A

goes from chiasm > thalamus> cortex

41
Q

what are the nerve bundles emerging from the chiasm called? Where do they end

A

the optic tracts. they end in the 2 lateral geniculate nuclei (LGN) in the thalamus

42
Q

where does LGN project

A

to the primary visual cortex (V1) via optic radiations

43
Q

where is the V1 located

A

in the occipital lobe

44
Q

how are visual areas in the brain organized? what does that mean?

A

retinotopically, meaning that neurons close to each other get information from close together parts of retina

45
Q

why does the fovea get a lot of space?

A

because it has many photoreceptors, bipolars, and ganglion cells, carrying lot of information

46
Q

fill in the blank.

a large proportion of visual cells in the brain receive and process data from ______ photoreceptors.

A

foveal

PSL300 (10 decks)

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