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MD1 Neuroscience > Retina > Flashcards

Retina Flashcards

(65 cards)

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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
To what is the output of horizontal cells?
Photoreceptors
26
What is the neurotransmitter released by horizontal cells?
GABA
27
How do horizontal cells respond to light?
Hyperpolarise
28
How many types of amacrine cells are there?
Many
29
Do amacrine cells have axons?
No
30
Why are amacrine cells considered mostly inhibitory?
Release glycine and GABA = inhibitory neurotransmitters
31
From what cells do amacrine cells receive input?
Bipolar cells
32
To what cells do amacrine cells send output?
Bipolar cells | Amacrine cells
33
Where are the cell bodies of ganglion cells located?
In ganglion cell layer
34
What are four types of ganglion cells?
ON OFF M P
35
What neurotransmitter do ganglion cells release?
Glutamate
36
Which neurons in the retina fire action potentials?
Ganglion cells
37
How do neurons that aren't ganglion cells transmit a signal?
Constantly releasing neurotransmitter Shifts in amounts with changes in membrane potential - Release more when depolarised - Release less when hyperpolarised
38
How do ganglion cells respond to light?
Increase/decrease action potential firing rate
39
What is the receptive field?
Area of retina that when stimulated with light changes cell's membrane potential
40
What type of receptive field do ganglion cells have?
Concentric centre-surround
41
What is the response to light when shone in the two different parts of the receptor field?
Centre's respond to light opposite to surround's response to light
42
What in a photoreceptor is activated by light?
Photopigment
43
What photopigment is in a rod?
Rhodopsin
44
What photopigment is in a cone?
Each type has different cone-opsin
45
What are opsins bound to?
All-trans retinal > derivative of vitamin A
46
What is the response of a photopigment to light?
Retinal absorbs light > changes shape > changes shape of attached opsin
47
Which segment of the photoreceptor contains the pigment?
Outer segment
48
What is the response of a photoreceptor to light?
Hyperpolarises
49
What is the neurotransmitter released by photoreceptors?
Glutamate
50
How does the amount of glutamate released change when photoreceptors respond to light?
Decreases
51
What is happening inside the cell during the dark current in a photoreceptor?
cGMP gates Na channel > continuous influx of Na > depolarisation of cell
52
What happens to cGMP inside a photoreceptor in the light?
Pigment activates transducin > transducin activates PDE > breaks downk cGMP > GMP > Na channel closes > membrane hyperpolarises
53
What type of bipolar cells are hyperpolarised by light?
OFF bipolar cells
54
What type of bipolar cells are depolarised by light?
ON bipolar cells
55
Why do different types of bipolar cells respond differently to glutamate?
Have different types of receptors - Ionotropic - Metabotropic
56
Which receptors depolarise a bipolar cell in response to glutamate?
Ionotropic - AMPA - Kainate - NMDA
57
Which receptors hyperpolarise a bipolar cell in response to glutamate?
Metabotropic | - mGluR6
58
Which type of ganglion cells do ON bipolar cells synapse with?
ON ganglion cells
59
Which type of ganglion cells do OFF bipolar cells synapse with?
OFF ganglion cells
60
What determines the receptive field centre response?
Through pathway
61
What determines the receptive field surround response?
Inputs from horizontal cells
62
What cells do horizontal cells receive input from?
Many photoreceptors
63
What cells do horizontal cells give output to?
Other photoreceptors
64
What neurotransmitter do horizontal cells release?
GABA
65
What determines the size of the receptive field surround?
Extent of electrical coupling between horizontal cells

MD1 Neuroscience (55 decks)

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