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Brain And behaviour (BIBB109) > Chapter 9 - Vision > Flashcards

Chapter 9 - Vision Flashcards

1
Q

What is in the optical system of the eye?

A

Cornea and lens

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2
Q

What does the optical system do?

A

Projects physical image of the world onto the retina

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3
Q

What does the retina do with the optical image?

A

It converts it into a neural image

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4
Q

What constitutes the retina?

A

3 interconnected layers and 5 classes of neurons

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5
Q

What are the 3 stages of vertical information flow?

A

1) Transduction of the image by photoreceptors (physical energy (photons) to electrochemical energy)
2) photoreceptors synapse on bipolar cells
3) bipolar cells synapse on ganglion cells

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6
Q

What is the lateral information flow?

A

At each stage of the vertical transmission there are specialized laterally connecting neurons called horizontal cells and amacrine cells.

These cells modify forward transmission across the synaptic layers ( largely by inhibition)

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7
Q

When are rods and cones depolarized?

A

When they are in darkness

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8
Q

In the rod, what maintains sodium and potassium concentrations?

A

Na/K pump

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9
Q

What happens to channels in outer segment when in the light?

A

Cell hyperpolarizes

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10
Q

What is the role of the visual pigment molecules?

A

Absorb electromagnetic energy and divert the energy into a biological process

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11
Q

What could you compare the rhodopsin to?

A

Is like a G-protein receptor

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12
Q

What could you compare retinal?

A

To a ligand (it’s a chromophore)

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13
Q

What are the steps of phototransduction?

A

1) Light stimulation of rhodopsin leads to activation of a G-protein, transducin
2) Activated G-protein activates cGMP phosphodiesterase (PDE)
3) cGMP binds Na+ channels opening them
4) PDE hydrolyzes cGMP, reducing its concentration
5) this leads to closure of sodium channels

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14
Q

Explain dark reaction

A

1) cGMP is high in cytoplasm
2) inward current of Na+ through cGMP-Gated channels which depolarized cell. This is the dark current which is usually ~ -50pA (in current) keeping cell’s Vm at ~ -40mV
3) depolarization causes transmitter release (glutamate) at terminal region

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15
Q

Explain light reaction

A

1) Light activates rhodopsin
2) Transducin, the g-protein is active
3) phosphodiesterase (PDE), the effector enzyme, is activated
4) PDE activity reduces the cGMP level
5) cGMP-gated N’a+ channels close- no Na+ current (dark current)
6) Cell hyperpolarizes to ~ -70mV, transmitter release stops

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16
Q

1) OFF bipolars are … by …/… by light

2) ON bipolars are … by…/… by light

A

1) depolarized — glutamate—hyperpolarized

2) hyperpolarized—glutamate—-depolarized

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17
Q

What are the two ways of thinking about the receptive fields’ visual system?

A

1- the set of photoreceptors to which the cell is connected

2- the set of the visual field in which various visual stimuli can affect the discharge rate of the cell (slide 39)

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18
Q

What are the two pathways of the receptive field? What are the components of each?

A

A) vertical pathway: - photoreceptors

  • bipolar cell
  • ganglion

Forms the center of receptor field (blue)

B) horizontal pathway: - photoreceptors

  • horizontal cells
  • bipolar cells
  • ganglion cell

Forms the inhibitory surround of receptive field

19
Q

What are the different types of ganglion cells?

A

M: large receptive fields, not wavelength selective, respond well to large objects and movement, terminate in M (magnocellular) layers of LGN

P: small receptive fields, selective to particular wavelengths of light (color), concerned with analysis of fine detail and color, terminate in P (parvocellular) layers of LGN

20
Q

What is scotopic vision?

A

Vision under dim-light (dark)

21
Q

What is photopic vision?

A

Vision under well lit conditions

22
Q

Name the parallel pathways

A

Magnocellular M(motion)

Parvocellular - P(shape, detail)

Koniocellular - non-M-non-P (color)

23
Q

For every point of the visual field we have at least 10 ganglion cells. What are they?

A
  • On-M
  • Off-M
  • On-P (2)
  • Off-P (2)
  • non-M-non-P (4)
24
Q

What does LGN stand for?

A

Lateral geniculate nucleus

25
Q

NonM-nonP ganglion cells project to which pet of the LGN

A

Koniocellular

26
Q

What is disparity tuning?

A

Many binocular cells code for retinal disparity - differences in images from the left and right eye that the brain uses as a binocular cue (stereopsis) to determine depth or distance of an object.

27
Q

What are the components of the horizontal organization of V1?

A

1) Occular dominance columns (cells in 4C are monocular)
2) orientation columns
3) cytochrome oxidase blobs

28
Q

What are receptive field properties emerging in V1?

A
  • Disparity tuning (for stereopsis, depth perception)
  • orientation tuning (for form perception)
  • direction selectivity (for lotion perception)
  • wavelength (color) selectivity (from retinal P pathway)
  • blobs - koniocellular pathway
29
Q

Which pathways continue to be segregated in parallel pathways?

A

M and P pathways are processed in segregated in parallel pathways by the visuals system

30
Q

What are the two streams of processing?

A

Dorsal and ventral

31
Q

Magnocellular Pathway

A 
M-type ganglion
Magnocellular LGN (Layer 1,2)
V1 Layer IV C alpha (monocular)
V1 Layer IV B (binocular)
dorsal pathway
32
Q

Where is motion represented?

A

It is represented in middle temporal area MT

33
Q

Are MT receptive fields larger than V1 r fields?

A

Yes, much larger

34
Q

Which neurons respond to optic flow stimuli?

A

MST neurons represent the motion of the world as you move through the world

35
Q

What is color constancy?

A

Our ability to determine the color of an object despite changing illumination

36
Q

Where are the cells responsible for color constancy located?

A

In V4

37
Q

Dorsal Pathway Explanation

A

“Where”

V1
V2
V3
MT - Motion
MST - navigation
other dorsal areas
38
Q

Rods vs Cones

A

Rods: High sensitivity to light
One type
Active in low light (scotopic)
Concentrated in peripheral retina

Cones: Low sensitivity to light
Three types (red, green blue)
Active in bright light (photopic)
Concentrated in central retina (fovea)

39
Q

P cell traits

A 
95% of ganglion cells
color sensitive
smaller receptive fields
slower adaptation
detect shapes + details
40
Q

M Cell Traits

A 
~5% of ganglion cells
color insensitive
larger receptive fields
rapid adaptation
detect motion
41
Q

Name 6 layers in LGN and what they do

A

1, 2 - Magnocellular

3, 4, 5, 6 - Parvocellular, some koniocellular

42
Q

Ventral Pathway

A 
"What"
V1
V2
V3
V4 (color vision)
Inferior Temporal (IT - face recognition))
other ventral areas
43
Q

Topographic Mapping in Visual System - Name and explanation

A

Retinotopic: Retinal cells in are close together, and the same in each layer, at the LGN level and cortex level

44
Q

Parvocellular Pathway

A

Perception of shape & detail

P-type ganglion
LGN Layer 3-6 Parvocellular
V1 Layer IV C Beta (monocular)
V1 Layer II & III (binocular)
Interblob

Brain And behaviour (BIBB109) (28 decks)

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