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Neuroscience > Retina > Flashcards

Flashcards in Retina Deck (42):
1

In which layer of the eyeball is the retina found?

Outer

2

Which structure of the eye is important for central vision?

Macula, which contains fovea

3

Which factors are fundamental to visual acuity?

Neural factors

Optic factors

4

What is visual acuity?

Ability to resolve fine detail

5

How is visual acuity tested?

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

Describe the optical factors that affect visual acuity?

Pupil size (smaller aperture = clearer vision)

Clarity of optical media (eg. cataracts)

Refractive errors (=blur)

7

What are photopic and scotopic light levels?

Photopic: well lit

Scotopic: low light levels 

8

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

Photopic: 6/6

Scotopic: 6/60

9

Which photoreceptors are acting in photopic vs scotopic light levels?

What impact does this have on visual acuity?

Photopic: cones > high visual acuity

Scotopic: rods > low visual acuity 

10

When is visual acuity highest? Why?

When looking straight ahead in photopic light levels

Utilising the fovea, which has the highest density of cones 

11

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

When looking to the side (slightly off centre)

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

12

List the neural cell types found in the retina?

Rods

Cones

Horizontal cells

Bipolar cells

Amacrine cells

Ganglion cells

13

What are the two synaptic layers of the retina?

Outer plexiform layer 

Inner plexiform layer 

14

At which stage in photoreception does light reach the photoreceptors?

Last

Light passes through all retinal layers before hitting photoreceptors 

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15

Describe the difference between rods and cones?

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16

Which photoreceptor type is more sensitive: rods or cones?

Rods

17

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?

Connectivity

18

Describe the wiring of neurons in the retina?

'Through' pathway: PRs-BCs-GCs

Lateral interactions: horizontal cells, amacrine cells

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19

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

First: photoreceptors

Second: bipolar cells

Third: ganglion cells

20

Where in the retinal pathway is the nerual signal modulated?

Two places: horizontal cells and amacrine cells

21

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

What is this layer important for?

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

Important for spatial vision and colour vision

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22

Where are bipolar cells found in the retina?

Inner nuclear layer

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23

Describe the different types of bipolar cells?

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

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24

Describe the action of horizontal cells in the retina?

Receive input from, and provide output to photoreceptors

Use GABA (inhibitory) > important for lateral inhibition 

Hyperpolarise in response to light 

25

Describe the action of amacrine cells in the retina?

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

 

26

Describe the appearrance of amacrine cells?

'Starburst' cells

Axonless

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27

Which neurons in the retina fire APs?

Only ganglion cells

28

How are signals in the retina transmitted?

Mostly graded potentials with NT release

Only ganglion cells use APs

29

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

Contains ganglion cell bodies and some displaced amacrine cells

 

30

What is the role of ganglion cells?

Main output neuron of retina

Release glutamate and fire APs

31

What are the different classes of ganglion cells?

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

M and P

32

What happens to the ganglion cell axons?

Travel down optic nerve and to higher brain centres 

33

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

Either depolarise (ON) or hyperpolarise (OFF)

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

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34

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

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

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35

What is the configuration of ganglion cell receptive fields?

Concentric-surround receptive fields 

36

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

Photopigments that are activated by light

Rods: rhodopsin

Cones: one of three different cone-opsins

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37

What do opsins bind to?

Vitamin A (all trans-retinal)

38

How do photoreceptors respond to light?

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

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39

Describe thHow do photoreceptors function in the dark?

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

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40

Describe the process of phototransduction?

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. 

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41

Which enzyme breaks down cGMP in phototransduction?

PDE: phosphodiesterase

42

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

Wiring of retina

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

Surround response: inputs from horizontal cells

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