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Neuroscience > Lecture 10 - introduction to visual pathways and circuits > Flashcards

Lecture 10 - introduction to visual pathways and circuits Flashcards

1
Q

What stream is concerned with the recognition of an object?

A

ventral (what) stream

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2
Q

What stream is concerned with spatial location?

A

dorsal (where) stream

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3
Q

What visible light range is our visual system sensitive to?

A

380nm (red) to 740nm (purple)

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4
Q

Describe the journey of light/information from entering the eye to the brain.

A
  1. information goes to the cornea
  2. anterior chamber
  3. pupil
  4. lens
  5. vitreous humour
  6. retina and fovea
  7. optic nerve
  8. brain
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5
Q

How is the retina organised?

A
  • seven cell types
  • three nuclear layers
  • 2 synaptic layers
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6
Q

What are the three nuclear layers of the retina?

A
  • outer nuclear layer
  • inner nuclear layer
  • ganglion cell layer
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7
Q

What type of cells does the ONL contain?

A

photoreceptors - rods and cones

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8
Q

What type of cells does the INL contain?

A

horizontal cells
bipolar cells
amacrine cells

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9
Q

What type of cell does the GCL contain?

A

ganglion cells

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10
Q

What are the 2 synaptic layers of the retina?

A
  • outer plexiform layer
  • inner plexiform layer
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11
Q

What does the OPL make connections between?

A

synaptic connections between photoreceptors, horizontal and bipolar cells

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12
Q

What does the IPL make connections between?

A

synaptic connections between bipolar, amacrine and ganglion cells.

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13
Q

What photoreceptors are responsible for peripheral vision?

A

rods (120 million) distributed through the retina

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14
Q

Describe rod cells.

A
  1. responsible for our ability to see in dim light (scotopic vision)
  2. high sensitivity
  3. monochromatic
  4. low resolution images
  5. good motion detection
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15
Q

What photoreceptors are responsible for central vision?

A

cones (6 million) concentrated around the fovea

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16
Q

Describe cone cells.

A
  1. work only in daylight (photopic vision)
  2. low sensitivity
  3. chromatic
  4. high spatial acuity
  5. narrow angle of coverage
17
Q

How many types of cone cells are there?

A

3 - S, M and L

18
Q

What are ganglion receptive fields?

A

each part of a scene is detected by many photoreceptors.
the receptive field is the part of the retinal ganglion cell that can gather information from the visual field

19
Q

What do ganglion cells respond best to and why is this important?

A

they respond best to contrast not light.
this means they have antagonistic centre-surround receptive fields (the centre must be mainly light while the surround mainly dark vice versa)

20
Q

Do ganglion cells on the fovea have a small or large receptive field?

A

small - can see more details

21
Q

Do ganglion cells in the periphery have a small or large receptive field?

A

large - can see less details

22
Q

Projections from the retina to central targets are organised in what fashion?

A

topographic

23
Q

What does LGN stand for?

A

lateral geniculate nucleus

24
Q

What is the role of the LGN?

A
  1. brings retinotopic maps from both eyes into register to make it easier for the cortex to combine inputs from the two eyes.
  2. other functions - not as well understood.
25
Q

Describe the primary visual cortex V1.

A

Stria of Gennari (band of myelinated axon (from LGN cells)) running parallel to the surface of the cortex along the calcimine fissure of the occipital lobe.

26
Q

How many layers does V1 have?

A

-6
- main input from LGN to layer IV

27
Q

How is the striate cortex organised?

A

in ocular dominance columns, alternating between left and right eyes

28
Q

What are the 3 main cell types in V1?

A
  1. simple cells
  2. complex cells
  3. hypercomplex cells
29
Q

Describe simple cells.

A
  • sum inputs from LGN with neighbouring RFs to build an elongated RF
  • orientation selective
  • monocular or binocular
  • have separate on and off subregions
  • perform length summation
30
Q

Describe complex cells.

A
  • receive input from simple cells
  • orientation selective
  • spatially homogenous RFs so no on/off subregions
  • nearly all binoculars
  • perform length summation
31
Q

Describe hypercomplex cells.

A
  • inhibitory flanks in the ends of RF
  • response increases with increasing bar length up to some limit
  • as the bar becomes longer, the response is inhibited.
32
Q

Describe the pathway of the ventral (what) stream.

A

V1 > ventral peristriate cortex > inferotemporal cortex

33
Q

Describe the pathway of the dorsal (where) stream.

A

V1 > dorsal peristriate cortex > posterior parietal cortex

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