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CNS CLERKSHIP > Physiology of Vision > Flashcards

Physiology of Vision Flashcards

1
Q

Describe the direct (vertical) for signal transmission of the retina.

A

Photoreceptors > Bipolar cells > Ganglion cells.

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2
Q

Describe the role of horizontal cells in the retina.

A
  • Receive input from photoreceptors and project to other photoreceptors and bipolar cells.
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3
Q

Describe the role of amacrine cells in the retina.

A
  • Receive input from bipolar cells and project to: ganglion cells, bipolar cells and other amacrine cells.
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4
Q

Light converts 11-cis-Retinal to what?

A

all-trans-Retinal (activated form).

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5
Q

Rhodopsin is made up of what?

A

Opsin + 11-cis-Retinal.

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6
Q

Another name for all-trans-RetinOl?

A

Vitamin A.

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7
Q

What facilitates seeing in dim light?

A

Rods.

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8
Q

What facilitates seeing in normal day light?

A

Cones.

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9
Q

Convergence in the rod system results in what?

A
  • Increasing sensitivity to light.

- Decreasing visual acuity.

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10
Q

What forms the basis of colour vision?

A
  • Cones.

- Different opsins for discrete wavelengths.

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11
Q

Short-wavelength cones see which colour?

A

Blue.

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12
Q

Medium-wavelength cones see which colour?

A

Green.

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13
Q

Long-wavelength cones see which colour?

A

Red.

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14
Q

Rods see which colour?

A

None.

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15
Q

Describe rods of the retina.

A
  • Achromatic.
  • Peripheral retina.
  • High convergence.
  • High light sensitivity.
  • Low visual acuity.
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16
Q

Describe cones of the retina.

A
  • Chromatic.
  • Central retina: fovea.
  • Low convergence.
  • Low light sensitivity.
  • High visual acuity.
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17
Q

Describe lateral inhibition.

A
  • Increases contrast and sharpness in visual response by exaggerating the difference in detected stimulus intensity by adjacent neurons.
  • Aids in localisation.
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18
Q

Lateral inhibition improves what?

A

Stimulus localisation.

19
Q

Horizontal cells connect “surround” neurons around the centre of each ganglion. This samples excitation in the surround and responds by releasing what?

A

GABA.

  • If low surround, less GABA released.
20
Q

What function does centre-surround organisation and lateral inhibition serve?

A

Emphasises areas of contrast i.e. sharpening boundary between objects of different luminance.

21
Q

Our visual system detects local differences in light what?

A

Intensity, not absolute amounts of light.

22
Q

Lateral inhibition modifies receptive fields of ganglion cells to have what?

A

Centre-surround organisation.

23
Q

Describe parallel processing of retinal output.

A

Simultaneous input from both eyes relays information to be compared in the cortex to allow for judging the depth and distance of an object.

24
Q

Describe “on-centre” cells of the retinal ganglia.

A

Stimulated when centre of its receptive field is exposed to light. Inhibited when the surround cells are exposed to light.

25
Q

Describe “off-centre” cells of the retinal ganglia.

A
  • Stimulated when surround cells are exposed to light.

- Inhibited when centre of receptive field is exposed to light.

26
Q

Each eye sees what part of the visual space?

A
  • Monocular visual field (+/- 45o).

NB the visual fields overlap to create a binocular visual field (+/-45o).

27
Q

The retina is divided in half relative to what?

A

The fovea.

28
Q

The retina is divided into what?

A
  • Nasal and temporal hemiretina.
29
Q

Nerve fibres from the nasal half of each retina cross over where?

A

The optic chiasm.

30
Q

Which optic tracts cross over at the optic chiasm?

A

Nasal (60%).

The temporal (40%) do not.

31
Q

Around half of the visual cortex is dedicated to information from what?

A

The fovea.

32
Q

The visual cortex is said to have what kind of organisation?

A

Visuotopic.

33
Q

With regards to input to the Striate cortex.

Magnocellular LGN neurons project to where?

A

Layer IVC-alpha.

34
Q

With regards to input to the Striate cortex.

Parvocellular LGN neurons project to where?

A

Layer IVC-beta.

35
Q

With regards to input to the Striate cortex.

Koniocellular LGN axons project to where?

A

Bypass layer IV to synapse in layers II and III.

36
Q

How may the synapses of koniocellular LGN axons in layers II and III of the striate cortex be observed?

A

As “blobs” following cytochrome oxidase staining.

37
Q

The first binocular neurons are found where?

A

In the striate cortex - most layer III neurons are binocular (but not layer IV).

38
Q

Cortical receptive fields contain what type of neurons?

A
  • Orientation selective neurons.
39
Q

Cortical receptive fields respond to what?

A

Light/dark bars or edges - ONLY if in a particular orientation.

40
Q

Peak frequency of Cortical receptive fields depends on what?

A

Angle and preferred orientation.

41
Q

Retinal synapses in LGN are not affected by deprivation, why?

A

Because they are monocular.

42
Q

In the cortex, monocular deprivation during a “critical period” in development results in what?

A

Active afferents in one eye and lower activity from the other.

43
Q

Sensory deprivation early in life can alter the structure of what?

A

The cerebral cortex.

CNS CLERKSHIP (43 decks)

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