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Physiology of vision and the visual system > Electrophysiology of the visual system > Flashcards

Electrophysiology of the visual system Flashcards

1
Q

When a photoreceptor becomes hyper-polarised (in light), how is the response transmitted throughout the photoreceptor to the synapse with the bipolar cell?

A

There is calcium influx along the length of the photoreceptor which is released at the synapse with Bipolar cells along with glutamate

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2
Q

What is an M (magnocellular) cell?

A

Large ganglion cell

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3
Q

What is a P (Parvocellular) cell?

A

Small ganglion cell

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4
Q

At which synapse are horizontal cells located?

A

At the synapse between photoreceptors and bipolar cells

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5
Q

At which synapse are amacrine cells present?

A

At the synapse between bipolar cells and ganglion cells

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6
Q

What percentage of all cones are long-medium (red-green wavelength) cones?

A

85%

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7
Q

How many cones must be stimulated for colour detection?

A

At least two, for wavelength discrimination

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8
Q

How is colour discriminated in the retina?

A

The stimulation of a blue (short wavelength cone) is compared to stimulation of a red-green (long) wavelength cone

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9
Q

Which photoreceptor detects dim light?

A

Rods

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9
Q

Which photoreceptor detects dim light?

A

Rods

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10
Q

Which photoreceptor detects bright light?

A

cones

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11
Q

Describe how rods connect to a ganglion cell

A

Rods connect indirectly to ganglion cells via cone bipolar cells

Multiple rods synapse with rod-bipolar cell which connects Amacrine II cells which connects to cone-bipolar cell which connects to ganglion cell

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12
Q

How are horizontal cells involved in isolating a stimulated photoreceptor?

A

Horizontal cells send a inhibitory stimulus to ganglion cells surrounding the stimulated photoreceptors

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13
Q

Are amacrine cells more numerous or horizontal cells?

A

Amacrine cells

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14
Q

How many types of amacrine cells are there?

A

29 types

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15
Q

Name some of the neurotransmitters used by Amacrine cells to modify the ganglion cell response.

A 
Dopamine 
Glutamate
Glycine
Acetylcholine
GABA
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16
Q

How many types of ganglion cells are there?

A

15

17
Q

What is the resting potential at the interface between the RPE and photoreceptors?

A

60mV

18
Q

what is the electro-oculogram?

A

It is a record of the electrical dipole occurring between the front and back of the eye.

19
Q

How is the current on a electro-oculogram reversed?

A

By moving the back and forth in horizontal direction

20
Q

How does bright illumination affect the height of the potential difference in a electro-oculogram?

A

Bright light increases the height of the potential difference

21
Q

When is the electro-oculogram lost?

A

In condition that disrupt the apposition of the RPE with the photoreceptor e.g. retinal detachment

22
Q

What is the electro-retinogram (ERG)?

A

Cumulative electrical response to light stimulus from all the retinal elements

23
Q

Where does the early receptor potential originate?

A

It originates from the photochemical reactions in the rod outer segments upon stimulation by light

24
Q

What is the early receptor potential dependent on?

A
  1. density of rods

2. high levels of unbleached rhodopsin

25
Q

What does the ERG begin with?

A

Early receptor potential

26
Q

Is the early receptor potential normally recorded?

A

No

27
Q

Is the early receptor potential recordable when the inner retina is destroyed but the outer retina is intact e.g. central retinal artery occlusion?

A

Yes

28
Q

What are the different waves of the electroretinogram (ERG)?

A
  1. a waves
  2. b waves
  3. oscillatory potentials
29
Q

What does the a wave in the ERG represent?

A

Hyperpolarisation of the photoreceptors inner segments

30
Q

Is the a wave in the ERG negative or positive?

A

negative

31
Q

Is the a1 wave in ERG for rods or cones?

A

cones

32
Q

Is the a2 wave in the ERG for rods or cones?

A

rods

33
Q

What does the b wave in the ERG represent?

A

bipolar cells

34
Q

Is the b1 wave in ERG from cone or receptor bipolar cells?

A

cone

35
Q

Is the b2 wave in the ERG from cone or rod bipolar cells?

A

Rods

36
Q

What pathology causes the b wave to be lost in the ERG?

A

retinal vascular conditions e.g. central retinal vein occlusion

37
Q

What do the oscillatory potentials in the ERG represent?

A

amacrine cells

38
Q

In what condition are oscillatory potentials lost in an ERG?

A

diabetes

39
Q

What is visual evoked potential (VEP)?

A

Records the electrical activity in the visual cortex following exposure to light stimulus

40
Q

How is a VEP recorded?

A

6 electrodes are placed around the left and right occipital cortices

Physiology of vision and the visual system (5 decks)

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