Visual System III

Question 1

Describe types of rgcs

Answer 1

More Than a dozen distinct types of rcgs
Each type tiles entire retina = creates multiple parallel labelled lines to lgn
Each labelled line conveys distinct types visual info
Esoteric

Question 2

what does each type of rgc do

Answer 2

Tiles retina
Each type = separate channel, labelled lines
Multiple labelled lines
Each ganglion cell = diff aspect visual perception

Question 3

name and describe the 3 main characterized channels from retina

Answer 3

Diff roles in high resolution and colour vision
Midget ganglion cells = 70% rgcs
Parasol ganglion cells = 10% of rgcs
Bistratified ganglion cells = 8% rgcs

Question 4

what happens in daylight to channels of rgcs

Answer 4

Each of tehse channels get its main inputs from cones

Question 5

what does human retina contain

Answer 5

3 types of cones = s m l
Each type tuned to respond best to a distinct range of wavelengths within visible spectrum

Question 6

describe colour spectrum

Answer 6

Diff wavelengths electromagnetic light
Blue = 445nm, shortest wavelength
Green = 535nm
Red - 575nm, longest wavelength

Question 7

name and describe what each colour cone responds to

Answer 7

S cones = responds best to blue
M cones = peak at green/yellow, medium wavelengths
L cones = red, long wavelengths
Note = all cones respond over a range, with peak= responds best to specific wavelength

Question 8

what Do we need for normal colour vision

Answer 8

Need all 3 cones
Colours = combos of cones so need all 3 to see all colours

Question 9

what makes colour cones dif

Answer 9

Diff opsins = proteins in each
Like one sensitive to blue wavelengths, one to green, one to red

Question 10

Describe colourblindness

Answer 10

Green and red cones = on X chromosome, if mutation = no second copy to compensate for men
= mutation in red opsin so no red cones
red green colour blind= no red or green opsin
If no red cones = can still tell red and blue, green and blue but not ebtween green and red, can tell short and long wavelengths but can’t tell small diff in long wavelengths of light = can’t tell red and green apart

Question 11

describe midget cells

Answer 11

70% ganglion cells, small, packed together in fovea
Small rfs bc center part formed by single cone
Go pod at resolving fine details

Question 12

what do midget cells convey

Answer 12

amoutn of red vs green in rd

Question 13

what are midget cells not good at

Answer 13

Detecting rapid changes

Question 14

Describe what midget cells synapse with

Answer 14

Synapse with parvocellular layers in lgn = p pathway (own labelled line - pathway - stays separate to cortex, retina —> thalamus —> cortex)
Which makes major contribution to cortical systems involved in processing of colour and form

Question 15

describe r vs green cones = midget cells

Answer 15

On cneter = colour in center activates
Off center = colour in center inhibits
(Red or green in each part)
= 4 configurations = tell us relative amount of red vs green in visual scene

Question 16

Describe Red on center green off center response pattern= to red vs green light

Answer 16

Increase firing to red light covering whole field = center on and surround does not respond much
Decrease firing to green light converting its rf = center does not much and surround = very responsive
=collectively either turned on or off by red or green= detect relative amounts of red and green

Question 17

Describe Red on center green off center response pattern = to white light

Answer 17

Increase firing if white light in center
Decrease firing if white light in surround
White light all over = no effect
= also acts as constrast detector
(White light = all colours of spectrum)
:. Tell red vs green and more generally acts as edge detectors - for differences in illumination = high res vision, edges and contrast and red vs green in scene

Question 18

describe parasol cells

Answer 18

Larger rfs
In foveal region
Not as dense
Center = multiple photorepcetros

Question 19

what do parasol cells convey

Answer 19

Achromatic signal = no colour discrimination
Lower spatial resolution, not as good for high res vision
But better for sensitivity to rapid changes in illumination

Question 20

Describe where parasol cells project

Answer 20

Project to magnocellular layers in lgn = m pathway (separate pathway, stays separate, separate labelled lines)
Contributes to cortical systems involved in analysis of location and movement

Question 21

describe receptive fields of parasol cells

Answer 21

Larger rfs
Center and surround get input form both red and green cones
So can’t tell diff between r vs g = no colour info conveyed
Important for conveying info about brightness and movement

Question 22

describe bistratified cells

Answer 22

Dendrites that get inputs from these bipolar cells = located in 2 diff regions of synaptic layer - inhibitory and excitatory regions of synaptic layer = why called bistratified
No cneter surround rf
Turned on or off by colours
Found near fovea

Question 23

what do bistratified Cells detect

Answer 23

amount of blue vs red/green (red+green = yellow)
= relative amounts of blue vs yellow
Ex = blue cones connected to on bipolar, yellow connected to off bipolar cell - connected to red and green cones = now this bistratified cell tuned off by yellow and on by blue and vice versa

Question 24

where do bistratified Cells project

Answer 24

Koniocellualr layers of lgn = k pathway
Involved in colour preception

Question 25

describr pattern of activation of bistratified Cell

Answer 25

Larger rfs Center and surround get input from both red and green cones Ex= blue on, yellow off = Turned on by blue light bc blue cones connected to on bipolar cell tuned off Turned off by yellow = bc red and green cones connected to off bipolar cell

Question 26

what cant a SINGLE cone do

Answer 26

Distinguish between wavelengths of light Ex = m cones respond best to green light but will also respond to wavelengths covering most of visible spectrum Cone = absorbs photons of light and hypoerlozies So this cone = also responds to high intensity blue and red light and low intensity green light Sooo need all 3 types of cones

Question 27

hwo is colour encoded in retina

Answer 27

By relative output of parasol, midget and bistratified cells 3 channels = L+m = parasol, luminance L-m = midget, red/green S-(l+m) = bistratified, blue/yellow Starting points= relative activation of tehse labelled lines = initial input Brain interprets relative activation of these 3 pathways to dtermine colour Combinatorial processing

Question 28

what is photoreceptor rf

Answer 28

Where light shines on retina

Question 29

what converges on individual rgcs

Answer 29

Info from multiple photorepcetors

Question 30

Compare rf of rgcs vs photoreceptors

Answer 30

Bc of convergence and complex circuitry of retina = rfs of rgcs are more complex (simple rfs combine —> more complex rf) than rfs of photorepcetros

Question 31

What do diff types of rgcs do

Answer 31

Tile retina Each cell type forms separate channel labeled line conveying a specific type of visual info

Question 32

What Do axons of rgcs do

Answer 32

Project as optic nerves to lgn At level of connections between retina and lgn

Question 33

describe fibers travelling to lgn

Answer 33

Fibers partially cross at optic chiasm Then continue as optic tracts (axons that go up to lgn)

Question 34

describe how we see = what projects where

Answer 34

Temporal part retina Nasal party of retina Ganglion cells take diff routes to get to lgn = temporal half stays on same side and nasal half crosses over to other side = ,left smiley face ends up in right part of brain = to contralateral lgn Does not really apply to fovea tho

Question 35

what do midget and parasol ganglion cells do

Answer 35

Project to 6 distinct layers in lgn (Make excitatory synapses on neurons in lgn, layers also reflect fact that the 2 eyes remain separate)

Question 36

what happens to inputs from both eyes and from midget and parasol cells in lgn

Answer 36

Diff pathways and eyes go through diff layers - separate all the way to cortex = inputs from the 2 eyes and from midget and parasol cells segregated in distinct layers of lgn

Question 37

where does ipsilateral eye project in lgn

Answer 37

Temporal region = no cross over = projects to layers 2,3 and 5 of isplaiteral lgn

Question 38

where does contralateral eye project in lgn

Answer 38

nasal region = projects to layers 1,4 and 6 of contralateral lgn

Question 39

where does M patwhay eye project in lgn

Answer 39

Layers 1 and 2

Question 40

where does p patwhay project in lgn

Answer 40

Layers 3,4,5,6

Question 41

where do bistratified rgcs project to in lgn

Answer 41

Project to lgn layers in-between the prominent magnocellualr and parvocellualr layers = regions referred to as koniocellualr layers - sparsely populated with small neurons (Cells between the 6 layers = koniocellualr cells)

Question 42

what does lgn do to inputs from rgcs

Answer 42

Lgn neurons faithfully relay inputs from rgcs to v1 Without significant changes in rfs (Diff pathways, eyes still stay separate)