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Neuroscience > Retina > Flashcards

Retina Flashcards

1
Q

In which layer of the eyeball is the retina found?

A

Outer

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2
Q

Which structure of the eye is important for central vision?

A

Macula, which contains fovea

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3
Q

Which factors are fundamental to visual acuity?

A

Neural factors

Optic factors

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4
Q

What is visual acuity?

A

Ability to resolve fine detail

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5
Q

How is visual acuity tested?

A

Recognition of letters on a Snellen or LogMAR chart

VA=D’/D, where D’=test distance and D=distance where each letter subtends 5 min arc

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6
Q

Describe the optical factors that affect visual acuity?

A

Pupil size (smaller aperture = clearer vision)

Clarity of optical media (eg. cataracts)

Refractive errors (=blur)

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7
Q

What are photopic and scotopic light levels?

A

Photopic: well lit

Scotopic: low light levels

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8
Q

What is the best visual acuity and photopic vs scotopic light levels?

A

Photopic: 6/6

Scotopic: 6/60

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9
Q

Which photoreceptors are acting in photopic vs scotopic light levels?

What impact does this have on visual acuity?

A

Photopic: cones > high visual acuity

Scotopic: rods > low visual acuity

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10
Q

When is visual acuity highest? Why?

A

When looking straight ahead in photopic light levels

Utilising the fovea, which has the highest density of cones

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11
Q

When is visual acuity best in scotopic light levels? Why?

A

When looking to the side (slightly off centre)

Higher density of rods just off to the side of the fovea

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12
Q

List the neural cell types found in the retina?

A

Rods

Cones

Horizontal cells

Bipolar cells

Amacrine cells

Ganglion cells

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13
Q

What are the two synaptic layers of the retina?

A

Outer plexiform layer

Inner plexiform layer

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14
Q

At which stage in photoreception does light reach the photoreceptors?

A

Last

Light passes through all retinal layers before hitting photoreceptors

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15
Q

Describe the difference between rods and cones?

A
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16
Q

Which photoreceptor type is more sensitive: rods or cones?

A

Rods

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17
Q

What is the broad explanation for why our day vision is much better than our night vision, even though rods are smaller, more numerous and more densely packed than cones?

A

Connectivity

18
Q

Describe the wiring of neurons in the retina?

A

‘Through’ pathway: PRs-BCs-GCs

Lateral interactions: horizontal cells, amacrine cells

19
Q

What are the first, second and third order neurons in the retina?

A

First: photoreceptors

Second: bipolar cells

Third: ganglion cells

20
Q

Where in the retinal pathway is the nerual signal modulated?

A

Two places: horizontal cells and amacrine cells

21
Q

Which cell type is located in the inner nuclear layer of the retina?

What is this layer important for?

A

Bipolar cells (1x rod bipolar cell, 9x cone bipolar cells)

Important for spatial vision and colour vision

22
Q

Where are bipolar cells found in the retina?

A

Inner nuclear layer

23
Q

Describe the different types of bipolar cells?

A

Defined by how they respond when light falls on the retina

ON BCs: depolarise when light hits retina

OFF BCs: hyperpolarise when light hits retina

24
Q

Describe the action of horizontal cells in the retina?

A

Receive input from, and provide output to photoreceptors

Use GABA (inhibitory) > important for lateral inhibition

Hyperpolarise in response to light

25
Q

Describe the action of amacrine cells in the retina?

A

Use glycine and GABA (inhibitory) > important for lateral inhibition

26
Q

Describe the appearrance of amacrine cells?

A

‘Starburst’ cells

Axonless

27
Q

Which neurons in the retina fire APs?

A

Only ganglion cells

28
Q

How are signals in the retina transmitted?

A

Mostly graded potentials with NT release

Only ganglion cells use APs

29
Q

Describe the content of the ganglion cell layer of the retina?

A

Contains ganglion cell bodies and some displaced amacrine cells

30
Q

What is the role of ganglion cells?

A

Main output neuron of retina

Release glutamate and fire APs

31
Q

What are the different classes of ganglion cells?

A

ON and OFF (depolarise/hyperpolarise when light hits retina)

M and P

32
Q

What happens to the ganglion cell axons?

A

Travel down optic nerve and to higher brain centres

33
Q

How do ganglion cells respond to light falling on the retina?

A

Either depolarise (ON) or hyperpolarise (OFF)

Adjust their firing rate depending on stimulation and which part of their receptive field stimulation occurs in

34
Q

What is the receptive field of a ganglion or bipolar cell?

A

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

35
Q

What is the configuration of ganglion cell receptive fields?

A

Concentric-surround receptive fields

36
Q

What do photoreceptors contain that allows them to respond to light?

A

Photopigments that are activated by light

Rods: rhodopsin

Cones: one of three different cone-opsins

37
Q

What do opsins bind to?

A

Vitamin A (all trans-retinal)

38
Q

How do photoreceptors respond to light?

A

cGMP breaks down to GMP > cGMP no longer gates Na channels > flow of Na ions ceases > cells hyperpolarise

Use graded potentials and glutamate, not APs

39
Q

Describe thHow do photoreceptors function in the dark?

A

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

40
Q

Describe the process of phototransduction?

A

Turning light signal into chemical signal

1) Light activates rhodopsin
2) Initiates a cascade of events that ultimately leads to the closure of cGMP gated Na channels:

Rh- > tranducin > PDE > breaks down cGMP

3) Closure of Na channels > HYPERPOLARISATION.

41
Q

Which enzyme breaks down cGMP in phototransduction?

A

PDE: phosphodiesterase

42
Q

What creates the centre-surround organisation of ganglion and bipolar cells?

A

Wiring of retina

Central response: through pathway (Ph-BC-GC)

Surround response: inputs from horizontal cells

Neuroscience (51 decks)

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