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2nd Year - Ophthalmology > Physiology 2 - Retina and Vision > Flashcards

Physiology 2 - Retina and Vision Flashcards

1
Q

What are the vision receptors and where are these located?

A

Rods and cones

In the retina

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2
Q

What cells do photoreceptors pass their signal to?

A

Bipolar cells

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3
Q

what cells do bipolar cells pass their signals to?

A

Ganglion cells

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4
Q

What is the order of photoreceptors, ganglion cells and bipolar cells from the front to the back of the eye?

A

Ganglion cells
Bipolar cells
Photoreceptors

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5
Q

What do ganglion cell axons project to the forebrain in?

A

The optic nerve

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6
Q

What cells receive input from photoreceptors and project to other photoreceptors and bipolar cells?

A

Horizontal cells

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7
Q

What cells receive input from bipolar cells and project to ganglion cells, bipolar cells and other cells the same type as it?

A

Amacrine cells

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8
Q

What is the purpose of photoreceptors?

A

To convert electromagnetic radiation to neural signals (transduction)

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9
Q

What are the 4 main regions of photoreceptors?

A

Outer segment
Inner segment
Cell body
Synaptic terminal

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10
Q

What are the 4 different types of photoreceptors?

A

Short-wave cone
Middle-wave cone
Long-wave cone
Rod

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11
Q

What type of photoreceptors have the longer outer segment?

A

Rod photoreceptors

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12
Q

What type of membrane potential do vertebrate photoreceptors have?

A

Depolarised rmp (Vm)

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13
Q

what is the approximate resting membrane potential of photoreceptors?

A

About -20mV

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14
Q

How does the resting membrane potential of photoreceptors compare to other neurones?

A

More positive

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15
Q

What happens to the membrane potential of photoreceptors on light exposure?

A

Membrane potential hyperpolarises

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16
Q

What causes the change in the membrane potential of photoreceptors due to light?

A

The “Dark Current”

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17
Q

What is the dark current?

A

A cGMP-gated Na+ channel that is open in the dark and closes in the light

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18
Q

What is the name of the visual pigment molecules?

What are these found in?

A 
Rhodopsin
Rods (present in membrane folds)
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19
Q

What is the purpose of Rhodopsin?

A

It is extremely sensitive light and therefore enables vision in low-light conditions

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20
Q

What are the 2 things that make up Rhodopsin?

A

Retinal (Vitamin A derivative)

Opsin (GPCR)

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21
Q

What does light do to Rhodopsin?

A

Converts 11-cis-retinal to all-trans-retinal (activated form)

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22
Q

What does all-trans-retinal cause?

A

Activates a molecular cascade which leads to decreased cGMP leading to closure of cGMP-gated Na+ channel -> hyperpolarisation

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23
Q

What molecule opens that dark current channel?

A

cGMP (nucleotide-gated channel)

24
Q

What molecule is the dark current permeable to?

A

Na+

25
Q

What neurotransmitter do photoreceptors release?

A

Glutamate

26
Q

What 2 factors largely determine visual acuity?

A

Photoreceptor spacing

Refractive power

27
Q

Do more photoreceptors lead to better or worse visual acuity?

A

Better

28
Q

What type of photoreceptors allow you to see in dim light?

A

Rods

29
Q

What type of photoreceptors allow you to see in normal daylight?

A

Cones

30
Q

What does a high convergence mean?

A

many rods feed into one ganglion with large spacing = over density (opposite for high)

31
Q

What does the higher convergence in rod system mean?

A

increased sensitivity whilst decreasing acuity

32
Q

What type of photoreceptors perceive colour?

A

Cones

33
Q

What colours do short-wave cones perceive?

A

Blue

34
Q

What colours do middle-wave cones perceive?

A

Green

35
Q

What colours do long-wave cones perceive?

A

Red

36
Q

Where are the rods mainly located on the retina?

A

peripheral retina

37
Q

Where on the retina are the cones mainly located?

A

Central retina (foevea)

38
Q

Do rods have a high or low convergence?

A

high

39
Q

Do cones have a high or low convergence?

A

Low

40
Q

Do rods or cones have a higher light sensitivity?

A

Rods

41
Q

Do rods or cones have a higher visual acuity?

A

Cones

42
Q

Does our visual system detect the absolute amount of light?

A

No, it detects the local differences in light intensity

43
Q

What is the name of the part of the visual space perceived by each eye?

A

Monocular visual field

44
Q

What is the name for the part of the visual space overlapped by both the eyes?

A

Binocular visual field

45
Q

What 2 halves can the retina be divided into?

A

A nasal and temporal hemiretina

46
Q

Where do the nerve fibres from the nasal half of each retina cross over?

A

At the optic chiasm

47
Q

How much of the visual field is perceived by both the eyes?

A

60% (the 2 retina)

48
Q

How does a discrete point of light activate many cells in the target structure?

A

Due to ovrelapping receptive fields

49
Q

What is perception of vision based on?

A

The brain’s interpretation of distributed patterns of activity

50
Q

What happens to the visual field in the brain? (what changes are made)

A

Left and right bifurcation and up and down invertion

51
Q

What part of the cortex does the right visual field do to?

A

Left cortex

52
Q

What part of the cortex does the superior visual field go to?

A

Lower cortex

53
Q

What is another name for the visual cortex?

A

Striate cortex

54
Q

What layer of the primary visual cortex are eye specific inputs segregated in?

A

Layer 4 (cells outside of layer 4 receive input from both eyes)

55
Q

What is amblyopia?

A

Cortical blindness = variety of visual disorders where the optics and retina of the eye are okay but one eye has better vision than the other

2nd Year - Ophthalmology (7 decks)

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