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MD1 Neuroscience > Retina > Flashcards

Retina Flashcards

1
Q

What fundamentally limits visual acuity?

A

Neural factors

Optical factors

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2
Q

What is visual acuity?

A

Ability to resolve fine detail

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3
Q

How do you test for visual acuity?

A

Recognition of letters on Snellen or LogMAR chart

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4
Q

How is visual acuity expressed?

A 
VA = D'/D, where:
D' = test distance
D = distance where each letter subtends 5 min arc
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5
Q

At what visual acuity are you legally blind?

A

6/60

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6
Q

What is the meaning of 6/12?

A

Person has to be 6 m away to see what normal people see at 12 m, even though letter is bigger

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7
Q

What are the optical factors affecting visual acuity?

A 
Pupil size
Clarity of optical media
- Cataracts
- Corneal opacities
Refractive errors
- Myopia
- Hypermetropia
- Astigmatism
- Presbyopia
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8
Q

What is the best visual acuity at photopic levels?

A

6/6

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9
Q

What determines central vision?

A

Density of cones in fovea

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10
Q

Are there many cones outside of the fovea?

A

No, not many

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11
Q

What is the best visual acuity at scotopic levels?

A

6/60

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12
Q

Where is night vision best?

A

Off-centre because highest density of rods 5-15 degrees away from fovea

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13
Q

What are the six neuron types of the retina?

A 
Rods
Cones
Horizontal cells
Bipolar cells
Amacrine cells
Ganglion cells
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14
Q

What are the synaptic layers of the retina?

A

Outer plexiform layer

Inner plexiform layer

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15
Q

What layers does light pass through before hitting the photoreceptors?

A

All

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16
Q

Describe rods

A 
Night vision
Scotopic
Very sensitive
One type only
No colour vision
95% of photoreceptors
Absent from fovea
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17
Q

Describe cones

A 
Day vision
Photopic
Less sensitive
Three types
- Red
- Green
- Blue
Allow colour vision
5% of photoreceptors
Densest in fovea
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18
Q

How is the retina wired up?

A

Through pathway: phtoreceptors > bipolar cells > ganglion cells
Lateral interactions > modulation
- Horizontal cells
- Amacrine cells

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19
Q

Which layer of the retina are horizontal cells located?

A

Outer

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20
Q

Which layer of the retina are amacrine cells located?

A

Inner

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21
Q

Which cells are the output neurons of the retina?

A

Ganglion cells

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22
Q

How many different types of bipolar cells are there?

A

10

  • 1x rod bipolar cell
  • 9x cone bipolar cell
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23
Q

What are bipolar cells important for?

A

Spatial vision

Colour vision

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24
Q

From what is the input to horizontal cells?

A

Photoreceptors

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25
Q

To what is the output of horizontal cells?

A

Photoreceptors

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26
Q

What is the neurotransmitter released by horizontal cells?

A

GABA

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27
Q

How do horizontal cells respond to light?

A

Hyperpolarise

28
Q

How many types of amacrine cells are there?

29
Q

Do amacrine cells have axons?

30
Q

Why are amacrine cells considered mostly inhibitory?

A

Release glycine and GABA = inhibitory neurotransmitters

31
Q

From what cells do amacrine cells receive input?

A

Bipolar cells

32
Q

To what cells do amacrine cells send output?

A

Bipolar cells

Amacrine cells

33
Q

Where are the cell bodies of ganglion cells located?

A

In ganglion cell layer

34
Q

What are four types of ganglion cells?

35
Q

What neurotransmitter do ganglion cells release?

36
Q

Which neurons in the retina fire action potentials?

A

Ganglion cells

37
Q

How do neurons that aren’t ganglion cells transmit a signal?

A

Constantly releasing neurotransmitter
Shifts in amounts with changes in membrane potential
- Release more when depolarised
- Release less when hyperpolarised

38
Q

How do ganglion cells respond to light?

A

Increase/decrease action potential firing rate

39
Q

What is the receptive field?

A

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

40
Q

What type of receptive field do ganglion cells have?

A

Concentric centre-surround

41
Q

What is the response to light when shone in the two different parts of the receptor field?

A

Centre’s respond to light opposite to surround’s response to light

42
Q

What in a photoreceptor is activated by light?

A

Photopigment

43
Q

What photopigment is in a rod?

44
Q

What photopigment is in a cone?

A

Each type has different cone-opsin

45
Q

What are opsins bound to?

A

All-trans retinal > derivative of vitamin A

46
Q

What is the response of a photopigment to light?

A

Retinal absorbs light > changes shape > changes shape of attached opsin

47
Q

Which segment of the photoreceptor contains the pigment?

A

Outer segment

48
Q

What is the response of a photoreceptor to light?

A

Hyperpolarises

49
Q

What is the neurotransmitter released by photoreceptors?

50
Q

How does the amount of glutamate released change when photoreceptors respond to light?

51
Q

What is happening inside the cell during the dark current in a photoreceptor?

A

cGMP gates Na channel > continuous influx of Na > depolarisation of cell

52
Q

What happens to cGMP inside a photoreceptor in the light?

A

Pigment activates transducin > transducin activates PDE > breaks downk cGMP > GMP > Na channel closes > membrane hyperpolarises

53
Q

What type of bipolar cells are hyperpolarised by light?

A

OFF bipolar cells

54
Q

What type of bipolar cells are depolarised by light?

A

ON bipolar cells

55
Q

Why do different types of bipolar cells respond differently to glutamate?

A

Have different types of receptors

  • Ionotropic
  • Metabotropic
56
Q

Which receptors depolarise a bipolar cell in response to glutamate?

A

Ionotropic

  • AMPA
  • Kainate
  • NMDA
57
Q

Which receptors hyperpolarise a bipolar cell in response to glutamate?

A

Metabotropic

- mGluR6

58
Q

Which type of ganglion cells do ON bipolar cells synapse with?

A

ON ganglion cells

59
Q

Which type of ganglion cells do OFF bipolar cells synapse with?

A

OFF ganglion cells

60
Q

What determines the receptive field centre response?

A

Through pathway

61
Q

What determines the receptive field surround response?

A

Inputs from horizontal cells

62
Q

What cells do horizontal cells receive input from?

A

Many photoreceptors

63
Q

What cells do horizontal cells give output to?

A

Other photoreceptors

64
Q

What neurotransmitter do horizontal cells release?

65
Q

What determines the size of the receptive field surround?

A

Extent of electrical coupling between horizontal cells

MD1 Neuroscience (55 decks)

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