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Neural Circuits and Behaviour > 4 - The Visual System > Flashcards

4 - The Visual System Flashcards

1
Q

What 3 types of stimuli does the visual system recognise?

A

Food, Predator, Mates.

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2
Q

Where does processing start in the eye?

A

The retina

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3
Q

What is the function of the retina?

A

Image Acquisition.

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4
Q

What structure pre-processes the visual information?

A

The lateral geniculate nucleus (LGN) while the main part happens in the visual cortex.

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5
Q

What are the 2 main visual pathways in the cortex?

A
  • Ventral - object feature stream “what” (inferior temporal)
  • Dorsal - Spatial location stream “where” (posterior parietal)
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6
Q

What regulates how much light enters the eye?

A

The Pupil

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7
Q

What focuses images onto the fovea?

A

The Lens

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8
Q

What is the fovea?

A

The part of the eye with the highest visual acuity and contains all the cones

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9
Q

How does light travel through the retina?

A

Through the muller cells, which are more transparent than other parts of the retina.

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10
Q

How many layer are in the retina and what are they?

A

5 layers
- 3 layers of neurons
- 2 layers of synapses (inner and outer plexiform layers)

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11
Q

What are the feedforward neurones in the retina?

A

Photoreceptors, Bipolar cells, Ganglion cells

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12
Q

What are the feedback neurones in the retina?

A

Horizontal cells and amacrine cells

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13
Q

Rods

A

Active in dim light

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14
Q

Cones

A

Active in bright light

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15
Q

Where does phototransduction happen in the retina?

A

In the outer segment

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16
Q

What is the key molecule responsible for phototransduction?

A

Cyclic GMP which activates specific ion channels in the cell.

17
Q

What is cGMP’s affect in the cell?

A

Raises the membrane potential by activating open channels. (Depolarisation)

18
Q

What converts cGMP to GMP?

A

Phosphodiesterase.

19
Q

What activates phosphodiesterase?

A

Light changing the conformation of rhodopsin which triggers a g-protein cascade.

20
Q

What molecule does photoreceptors release?

A

Glutamate.

21
Q

When is less glutamate released?

A

In the light during hyperpolarisation.

22
Q

How are the neurones below photoreceptors hyperpolarised?

A

The cells that synapse with the photoreceptors receive less glutamate.

23
Q

On cells…

A

Depolarise when the light intensity increases.

24
Q

Off cells…

A

Hyperpolarises when the light intensity increases.

25
Q

What is the mechanism of on cell activation?

A
  • They use mGluR instead of AMPAR and cGMP is not required for ion channels to close.
  • TRPM1 is expressed in on cells and not off cells
26
Q

What molecules are required for light and glutamate responses in On cells?

A

Nycalopin and Proteglycan

27
Q

Where do the off cells project in the inner plexiform layer?

A

To the layer closest to the bipolar cells.

28
Q

Where do the on cells project in the outer plexiform layer?

A

Into the part that is closer to the ganglion cell layer.

29
Q

When do retinal ganglion cells fire action potentials?

A

When specific areas of the retina are illuminated.

30
Q

What is the receptive field?

A

An area in the retina where when illuminated activates a visual neurone.

31
Q

What is centre-surround organisation of the receptive field?

A

What many visual neurons have, illumination of the centre and the surroundings leads to responses in opposite polarities.

32
Q

What is the mechanism of centre surround organisation?

A
  • Many photoreceptors converge to one bipolar cell.
  • Some activate directly which is centre.
  • Others activate via horizontal cells which is surround causing depolarisation.
33
Q

What other cells have centre surround organisation?

A

Ganglion cells.

34
Q

In Off centre ganglion cells..

A

Action potentials stop spiking when the light is central.

35
Q

In On centre ganglion cells…

A

Action potentials spike when the light is in the centre and decreases when light is in the surround.

36
Q

What do on and off centre ganglion cells in diffuse light?

A

No response.

37
Q

What are the 2 classes of ganglion cells?

A

Parvocellular and magnocellular.

38
Q

Characteristics of parvocellular cells

A

They have a smaller dendritic tree and a smaller receptive field.

Neural Circuits and Behaviour (11 decks)

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