Lecture 4 - visual system

Question 1

what does each layer of neurons contain?

Answer 1

some neurons with positive projections and negative feedback of downstream level back by inhibitory neurons and negative feedforward

Question 2

main function of the retina

Answer 2

image acquisition and send to the brain

Question 3

lateral geniculate nucleus (LGN)

Answer 3

another pre-processing sensor and processing visual information before the cortex

Question 4

where does the main processing of information happen?

Answer 4

in the visual cortex

Question 5

ventral stream pathway

Answer 5

1. ventral stream is V1,V2 and V4 and involved in object identity located in inferior temporal lobe

Question 6

dorsal stream pathway

Answer 6

dorsal stream is localizing object for speed and direction and is responsible for spatial location

Question 7

what are the 5 layers of the retina

Answer 7

consists of 3 layers of neurons and 2 layers of synpases

Question 8

signalling in the retina

Answer 8

photoreceptors signal with bipolar cells which signal with ganglion cells

Question 9

what activates the ganglion cells?

Answer 9

glutamate expressed in the bipolar cells

Question 10

what inhibits the ganglion cells?

Answer 10

GABA expressed by Amacrine cells which send information back and forward

Question 11

what are the feedforward neurons?

Answer 11

photoreceptors, bipolar cells and ganglion cells

Question 12

what are the feedback neurons

Answer 12

horizontal cells and amacrine cells

Question 13

what does the outer plexiform layer consist of?

Answer 13

consists of synapses between photoreceptors, bipolar cells and horizontal cells

Question 14

what does the inner plexiform layer consist of?

Answer 14

consists of synapses between bipolar cells, amacrine cells and ganglion cells

Question 15

what does bipolar cells and horizontal cells receive their input from? (laminar organisation)

Answer 15

photoreceptors in outer plexiform layer

Question 16

what does ganglion cells and amacrine cells receive their input from?

Answer 16

bipolar cells (and ganglion cells from amacrine cells) in the inner plexiform layer

Question 17

rods vs cones

Answer 17

rods are active at dim light and cones are active at bright light

Question 18

where does phototransduction happen?

Answer 18

in the outer segment (disks)

Question 19

what do photoreceptors do?

Answer 19

respond to bright flashes by hypolarisation, a decrease in membrane potential. they allow efficient release of glutamate

Question 20

what is the key molecule in phototransduction?

Answer 20

cGMP which activates specific ion channels on the membrane

Question 21

what happens in darkness? (phototransduction)

Answer 21

there is lots of cGMP which actviates a channel and when it opens the membrane depolarises and membrane potential increases

Question 22

what happens when cGMP is converted to GMP? (phototransuction)

Answer 22

channel closes and membrane potential decreases which involves rhodopsin

Question 23

what does light cause in photoreceptors?

Answer 23

causes a conformational change in rhodopsin and triggers a G protein cascade which leads to a decrease in amount of cGMP and closes the channel

Question 24

what makes photoreceptor synapses special?

Answer 24

have special structures where they can sustain a consistent release of glutamate

Question 25

what decrease glutamate release?

Answer 25

light activation

Question 26

ON bipolar cells vs OFF bipolar cells

Answer 26

ON bipolar cells depolarise when activated by light and OFF bipolar cells hyperpolarise

Question 27

mechanism of ON cell activation

Answer 27

- express mGluR instead of AMPAR to signal a cascade - G protein not the same as photoreceptor cascade - removal of cGMP is not required for ion channel closure - TRMP1 expressed in ON cells

Question 28

what is required for light and glutamate response in ON cells

Answer 28

Nyctalopin and protrohylcan

Question 29

what are located in the same sublaminae in IPL?

Answer 29

axons of ON bipolar cells and dendrites of ON ganglion cells and amacrine cells

Question 30

what is the receptive field?

Answer 30

area in the retina which when illuminated activates a visual neuron

Question 31

center-surround organisation

Answer 31

center-surround of receptive field means the center and the surrounding area leads to responses in opposite polarities

Question 32

which visual cells have center-surround of receptive field

Answer 32

bipolar and ganglion cells

Question 33

annulus

Answer 33

this is the outer part of the receptive field

Question 34

inputs at the center vs inputs at the outer part

Answer 34

inputs at the center signal directly with bipolar cells and ones on the outer part indirectly bind with bipolar cells using horizontal cells

Question 35

stimulating the center of receptive field (bipolar cell)

Answer 35

stimulating the centre of receptive field, only stimulates the center

Question 36

stimulating outer part of receptive field (bipolar cells)

Answer 36

if surrounding area is stimulated, it stimulates the outer photoreceptors to cause a reverse effect and depolarisation

Question 37

illuminating the whole receptive field in ganglion cells

Answer 37

this does not activate ganglion cells - designed to respond to differences in illumination within receptive field

Question 38

stimulation of OFF center

Answer 38

they stop spiking and when the light decreases, they start spiking again

Question 39

stimulation of ON center

Answer 39

when stimulating the ON center, there is increase in spiking rate and when light decreases they stop spiking

Question 40

what is center-surroun organisation the result of?

Answer 40

results from inhibitory feedback from amacrine cells

Question 41

what are the two main classes of ganglion cells?

Answer 41

parvocellular (80%) and magnocellular (10%)

Question 42

parvocellular vs magnocellular

Answer 42

parvocellular has smaller dendritic trees and can distinguish the different colours of light

Question 43

parvocellular vs magnocellular (processing information)

Answer 43

parvocellular process information about shape and colour. magnocellular process information about motion

Question 44

cones received by parvocellular cells

Answer 44

can receive red cones in the center and green cones in the surrounding part

Question 45

morphology of ganglion cells dendritic trees

Answer 45

- differ in size of dendritic tree where smaller trees process more detailed information - can be asymmetric

Question 46

where does adaptation originate

Answer 46

in the retina and downstream

Question 47

adaptation vs sensitisation

Answer 47

adaptation results in a decrease in spiking where sensitisation results in an increased spiking. adaptation for visual illusions