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Neuroscience > L27 The Retina > Flashcards

L27 The Retina Flashcards

1
Q

what makes up the structure of the photoreceptors?

A

outer segment

inner segment

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2
Q

describe the outer segment of the photoreceptors

A

they are oriented towards the RPE

contain visual pigment for photoreceptor transduction

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3
Q

describe the inner segment of the photoreceptors

A

directed toward the inside/center of eyeball

forms synapses which transmit the visual info on the retinal cells (bipolar/horizontal cells)

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4
Q

what NT is released from retinal photoreceptors?

A

glutamate

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5
Q

is glutamate released in the light or dark?

A

dark - light reduces the release of glutamate

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6
Q

what is disk shedding?

A

the outer segment renews disks from the bottom up

the top disks are shed and phagocytozed by RPE cells

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7
Q

what is the main function of rods? describe the characteristics

A

to enable vision in the dark ->
cellular amplification mechanism is well developed which increases light sensitivity
temporal summation is poor (distinguish between 2 flashes of light)
convergence is high
only 1 type

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8
Q

what are the characteristics of cones

A

amplification is low = less sensitive to light
works better in bright conditions
3 different types of cones that allow color vision
convergence is low = increasing spatial resolution (visual acuity) showing better vision in the light

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9
Q

are rods and cones evenly distributed?

A

NO

NO rods in the FOVEA = no central vision in the dark

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10
Q

what is rhodopsin

A

the visual pigment of rods (2 components)

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11
Q

what are the 2 components of rhodopsin?

A

opsin

retinal

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12
Q

what is opsin

A

protein synthesized in the photoreceptor

have 7 membrane spanning domains

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13
Q

what is retinal

A

light absorbing compound derived from vitamin A and is the chromopore of the visual pigment

covalently attached to the 7th domain of opsin

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14
Q

what is the mechanism that occurs in the dark

A

visual pigment inactive– G-protein inactive – cGMP phosphodiesterase inactive – intracellular cGMP CAN gate the cGMP-gated Na+ channel to OPEN = depolarization — glutamate released

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15
Q

when do photoreceptors depolarize

A

in the dark

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16
Q

when do photoreceptors hyperpolarize?

A

in the light

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17
Q

what is the mechanism that occurs in the light

A

visual pigment active – G-protein (transducin) active – cGMP phosphodiesterase – metabolizes intracellular cGMP – close Na+ channel - hyperpolarize == stopping glutamate!

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18
Q

describe blue cones

A

aka S cones

have max sensitivity to short waves 430 nm = BLUE light

19
Q

describe green cones

A

aka M cones

max sensitivity to medium waves 530 nm = GREEN light

20
Q

describe red cones

A

aka L-cones

max sensitivity to long waves 560 nm = RED light

21
Q

where is rhodopsin park of

A

disk membrane of photoreceptors

22
Q

what is the first step in the phototransduction process in the absorbtion of light

A

absorption of light causes a conformational change of the retinal molecules from inactive 11-cis isomer –> active all-trans isomer

23
Q

describe relative stimulation

A

relative hyperpolarization of the different cones will determine the color perception of the person

there is a mix of stimulation though regardless of the color, there is at least some stimulation of ALL THREE

24
Q

what is the visible range of light

A

400-700nm

25
Q

what is monochromatic light

A

light with only 1 wavelength - very rare
occurs in different bands of rainbow
artificial light produced by a laser

26
Q

what are the 5 major cells in the retina

A 
retinal photoreceptors
bipolar cells
horizontal cels
amacrine cells
retainal ganglion cells
27
Q

describe retinal photoreceptors

A

rods and cones
are hte input cells of the retina
depolarized during dark
hyperpolarized during light

28
Q

describe bipolar cells

A

retinal photoreceptors synapse on these

in the outer plexiform layers which transmits their info to the inner plexiform layer on the retinal ganglion cells

29
Q

describe horizontal cells

A

crucial for the “indirect” wiring pathway and are responsible for “lateral” inhibition

30
Q

describe amacrine cell

A

work like the horizontal cells only they are found in the inner plexiform layer

31
Q

describe retinal ganglion cells

A

output cells of the retina

transmit info to the LGN via the optic nerve, chiasm and tracts

32
Q

why are on bipolar cells called that

A

because they are depolarized in the light is ON

33
Q

why are off bipolar cells called that

A

because they are depolarized in the dark when the light is OFF

34
Q

what does the depolarization or hyperpolarization of the bipolar cells depend on

A

the synapse between the photoreceptor and the bipolar cells

35
Q

describe off bipolar cells

A

have ionotropic glutamate receptos which is stimulated by the release of glutamate = depolarize the cell

36
Q

describe on bipolar cells

A

metabotropic glutamate receptors which have an inhibitory effect when stimulated by the release of glutamate form photoreceptors

37
Q

describe horizontal cells

A

responsible for the lateral inhibitory effect needed to depolarize an ON bipolar cells in the event that light has not been places directly in its receptive field but in the surrounding area

38
Q

what is retinitis pigmentosa

A

genetic disease in which rods preferentially degenerate
night blindness = earliest symptoms
peripheral vision
tunnel vision
total blindness
accumulation of pigment seen in exam
photoreceptor degeneration is not cleaned up by phagocytes of the RPE

39
Q

what is night blindness

A

nyctalopia
effects vitamin A deficient people as the retinal is derived from it
a very necessary part of opsin/retinal combinatin that forms the photoreceptor pigment

40
Q

what is color blindness

A

lack of a particular type of cone
most common is x-linked red-green color blindness prevalent in males
protanopia - loss of red cone
deuteranopia - loss of the green cone

41
Q

define scotoma?

A

area of lost or depressed vision within the visual field, surrounded by an area of less depressed or normal vision (pathologic blind spot)

42
Q

define temporal resolution

A

the ability to distinguish subsequent stimuli from each other (temporal: relating to time)

43
Q

define spatial resolution

A

the ability to distinguish adjacent stimuli from each other (spatial: relating to space)

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