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Neuroscience > The Retina > Flashcards

The Retina Flashcards

1
Q

What are the factors that determine visual acuity?

A

Neural factors and optical factors

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2
Q

What is visual acuity?

A

Ability to resolve fine detail

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3
Q

What does the denominator of visual acuity mean eg 6/12?

A

What a normal person sees at 12m, this person sees at 6m (this is the legal driving limit)

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4
Q

What are the optical factors that affect visual acuity?

A

pupil size; clarity of optical media: cataracts, corneal opacities; refractive errors (cause blurriness): usually caused by length of eyeball eg myopia, hypermetropia, astigmatism, presbyopia

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5
Q

Visual acuity is defined by

A

density of cones; tf fovea has highest visual acuity

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6
Q

Phototopic light levels

A

daylight

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7
Q

Scotopic light levels

A

dark light levels

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8
Q

At phototopic light levels, the best VA is

A

6/6 or better

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9
Q

At scotopic light levels, the best VA is

A

6/60

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10
Q

Visual acuity decreases as you move away from the fovea proportional to

A

decrease in cones

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11
Q

T/F The best visual acuity under scotopic conditions is at the fovea

A

False; it’s about 8 degrees from the fovea where the concentration of rods is increasing

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12
Q

What are the 6 types of neurons in the retina?

A

rods, cones, horizontal cells (HCs), bipolar cells (BCs), amacrine cells (ACs), and ganglion cells (GCs)

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13
Q

The output neurons of the retina are

A

ganglion cells (GCs)

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14
Q

Where in the retina do the neurons synapse?

A

Outer and inner plexiform layers

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15
Q

T/F Photoreceptors are the first cells light hits

A

False; they are the LAST cells, at the back of the retinal layers

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16
Q

95% of photoreceptors are

A

rods

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17
Q

T/F Rods are more sensitive to light than cones

A

True

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18
Q

What are the 3 types of cones?

A

Red, green, and blue

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19
Q

What is the order of layers in the retina from where light contacts it?

A

nerve fibre layer
ganglion cell layer
inner plexiform layer (bipolar-amacrine-ganglion synapses)
inner nuclear layer (nuclei of horizontal, bipolar, and amacrine cells)
outer plexiform layer (bipolar-horizontal-photoreceptor synapses)
outer nuclear layer (nuclei of photoreceptors)
photoreceptor layer
pigment epithelium
choroid

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20
Q

Bipolar cells are in which layer of the retina?

A

Inner nuclear layer

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21
Q

What are the 10 different types of bipolar cells?

A

1x for rods; 9x for cones

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22
Q

Bipolar cells are important for

A

spatial vision and colour vision

23
Q

OFF BCs

A

always HYPERpolarize when light shines on the retina

24
Q

ON BCs

A

always DEpolarize when light falls on the retina

25
Q

Bipolar cells (BCs) receive inout from

A

photoreceptors

26
Q

What is the function of horizontal cells?

A

modulation in outer retina: receive input from photoreceptors and provide output to other photoreceptors - mainly INHIBITORY

27
Q

Horizontal cells are mainly __________ to photoreceptors

A

Inhibitory, via GABA

28
Q

Horizontal cells use which NT?

A

GABA tf inhibitory

29
Q

Horizontal cells respond to light by

A

HYPERpolarizing

30
Q

ON ganglion cells

A

DEpolarize when light falls on the retina

31
Q

OFF ganglion cells

A

HYPERpolarize when light falls on the retina

32
Q

What is unique about ganglion cells in the retina?

A

They are the only cells that fire APs; the rest of the retina fires only graded potentials

33
Q

Ganglion cells release

A

Glutamate (excitatory)

34
Q

What is the role of ganglion cells?

A

Main output neuron of the retina

35
Q

T/F The visual system is a detection system

A

False; it is a comparator - how we interpret what we see (greyness, colour, motion) relates to the context in which it is presented

36
Q

What is meant by receptive field of a ganglion cell or bipolar cell?

A

area of retina that when stimulated with light changes the cell’s membrane potential

37
Q

T/F Ganglion cells respond to light by firing action potentials

A

False; GCs respond to light by increasing or decreasing their AP firing rate - depending on where in the receptive field the light is shone

38
Q

What are photopigments?

A

Proteins in photoreceptors: rods contain rhodopsin, cones contain cone-opsins (1 of 3) - all bind to vitamin A (retinal); they convert light into neural signals

39
Q

How do photoreceptors turn light into neural signals?

A

Photopigments (rhodopsin, coneopsins) are conformationally changed when light interacts with their bound retinal

40
Q

Photoreceptors release NT relative to

A

graded membrane potential; lower (hyperpolarized/more negatie) means less firing and less release of NT

41
Q

Photoreceptors

A

HYPERpolarize in response to light

42
Q

Photoreceptors use ________ as their NT

A

glutamate (excitatory)

43
Q

In the dark, photoreceptors are ___________ due to _________

A

depolarized; Na+ cycling in and out of the photoreceptors via cGMP-gated channels

44
Q

In the light, photoreceptors are _________ due to _________

A

hyperpolarized; phototransduction leads to formation of PDE which breaks down cGMP, closing the Na+ channel thus the cell hyperpolarizes

45
Q

What is phototransduction?

A

Light activates rhodopsin via vitamin A; this initiates the production of transducin, then PDE; PDE breaks down cGMP that, in the dark, keeps cGMP Na+ channels open (depolarizes cell); the cGMP Na+ channels close, leading to hyperpolarization of the cell

46
Q

The photoreceptors that form the central part of a ganglion cell receptive field are

A

those that directly contact ganglion cells via bipolar cells ie Ph-BC-GCs

47
Q

The central response is generated by

A

light contacting photoreceptors in the central part of the ganglion cell receptive field

48
Q

The central response of ganglion cells to light is

A

depolarization

49
Q

The receptive field of a retinal ganglion cell is

A

the area of retina that the ganglion cell will respond to

50
Q

Light shone on the periphery of a receptive field generates the _______ response

A

surround response

51
Q

The surround response is generated by

A

shining light on the periphery of a ganglion cell receptive field

52
Q

Photoreceptors in the surround send information to

A

horizontal cells

53
Q

Which cell type creates the ‘centre-surround’?

A

Horizontal cells

Neuroscience (15 decks)

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