Retina Flashcards Preview

MD1 Neuroscience > Retina > Flashcards

Flashcards in Retina Deck (65):
1

What fundamentally limits visual acuity?

Neural factors
Optical factors

2

What is visual acuity?

Ability to resolve fine detail

3

How do you test for visual acuity?

Recognition of letters on Snellen or LogMAR chart

4

How is visual acuity expressed?

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

5

At what visual acuity are you legally blind?

6/60

6

What is the meaning of 6/12?

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

7

What are the optical factors affecting visual acuity?

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

8

What is the best visual acuity at photopic levels?

6/6

9

What determines central vision?

Density of cones in fovea

10

Are there many cones outside of the fovea?

No, not many

11

What is the best visual acuity at scotopic levels?

6/60

12

Where is night vision best?

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

13

What are the six neuron types of the retina?

Rods
Cones
Horizontal cells
Bipolar cells
Amacrine cells
Ganglion cells

14

What are the synaptic layers of the retina?

Outer plexiform layer
Inner plexiform layer

15

What layers does light pass through before hitting the photoreceptors?

All

16

Describe rods

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

17

Describe cones

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

18

How is the retina wired up?

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

19

Which layer of the retina are horizontal cells located?

Outer

20

Which layer of the retina are amacrine cells located?

Inner

21

Which cells are the output neurons of the retina?

Ganglion cells

22

How many different types of bipolar cells are there?

10
- 1x rod bipolar cell
- 9x cone bipolar cell

23

What are bipolar cells important for?

Spatial vision
Colour vision

24

From what is the input to horizontal cells?

Photoreceptors

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

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