L3 - overview of the visual system

Question 1

3 types of stimuli for visual system

Answer 1

food
predator
mate

Question 2

what is negative feedforward

Answer 2

when GABA neurons activate neurons downstream

Question 3

what is meant by - the optic nerve is an information bottleneck

Answer 3

it cannot process everything that the retina acquires rejects a lot of information

Question 4

functions of the retina

Answer 4

image acquisition

filters information and adapts

Question 5

what is the function of the lateral geniculate nucleus (LGN)

Answer 5

preprocesses the visual information - deep in brain so difficult to research

Question 6

function of visual cortex

Answer 6

place of main processing of information

Question 7

2 main visual pathways in the cortex

Answer 7

ventral stream and dorsal stream

the two influence each other

Question 8

ventral stream

Answer 8

used to process object identity (what), terminates in the inferior temporal complex

Question 9

dorsal stream

Answer 9

used to process information about the location, speed, direction of the object (where). terminates in the posterior parietal complex

Question 10

function of the pupil

Answer 10

regulates amount of light that falls on the retina

Question 11

function of the lens

Answer 11

focuses the image on the fovea (part of the retina)

Question 12

what is the fovea

Answer 12

part of the retina with the highest visual acuity

Question 13

what does light travel through

Answer 13

transparent muller cells within the retina

Question 14

layout pf the retina

Answer 14

3 layers of neurons and 2 layers of synapses
feedforward neurons - photoreceptors, bipolar cells and ganglion cells
feedback neurons - horizontal cells and amacrine cells

Question 15

pathway through the retina

Answer 15

info starts in photoreceptors
goes to bipolar cells
goes to ganglion cells
goes through optic nerve to the brain

Question 16

what are the two levels of synapses in the brain

Answer 16

inner and outer plexiform layers

Question 17

what is the outer plexiform layer

Answer 17

contains synapses between photoreceptors, bipolar cells and horizontal cells

Question 18

what is the inner plexiform layer

Answer 18

contains synapses between bipolar cells, amacrine cells and horizontal cells

Question 19

what is active and dim light and what is active at bright light

Answer 19

rods active at dim light

cones active at bright light

Question 20

where does phototransduction occur

Answer 20

in the outer segment of rods and cones

photoreceptors respond to light flashes by hyper polarisation

Question 21

phototransduction cascade

Answer 21

1) shine light on photoreceptor, opsin change their conformation
2) activates the G-protein coupled receptors
3) G alpha subunit dissociates which activates phosphodiesterase
4) phosphodiesterase causes a drop in the concentration of cyclic GMP
5) decrease in cGMP causes a closing of the change;s
6) closing of the channels causes hyper polarisation of the membrane

Question 22

what is the phototransduction cascade sensed by

Answer 22

hyperpolarisation causes a decrease in glutamate release
glutamate concentration sensed by bipolar and horizontal cells
less glutamate = less. activation of bipolar and horizontal cells

Question 23

what are the two types of bipolar cells

Answer 23

ON cells - depolarise when light intensity increases

OFF cells - hyper polarise when light intensity increases

Question 24

what does less glutamate lead to regarding OFF cells

Answer 24

less glutamate leads to less depolarisation of OFF cells therefore they hyperpolarse

Question 25

what receptors do OFF cells express

Answer 25

ionotropic glutamate receptors (excitatory) coupled to G-proteins - leads to less closing of channels

Question 26

what receptors do ON cells express

Answer 26

metabotropic glutamate receptors (inhibitory) - AMPA

Question 27

what is a receptive field

Answer 27

an area in the retina which when illuminated activates a visual neuron

Question 28

what is center-surround organisation

Answer 28

illumination of the centre and the surround leads to responses in opposite polarities

Question 29

what cells have centre surround organisation of their receptive field

Answer 29

bipolar and ganglion cells

Question 30

what occurs during stimulation of the centre of the receptive field of an ON cell

Answer 30

get a depolarisation and if stimulate away from the centre get a hyper polarisation

Question 31

stimulation of an OFF cell with spot and annulus

Answer 31

spot = hyperpolarisation
annulus = depolarisation

Question 32

bipolar cells receive input from what 2 cells

Answer 32

photoreceptors activate directly and indirectly
direct - located in centre of receptive field, leads to hyperpolarisation of OFF cell
indirect - stimulation of surrounding photoreceptors causes inhibition of horizontal cell - no longer inhibits bipolar cell leads to depolarisation

Question 33

what are located in the same subliminal in the IPL

Answer 33

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

Question 34

large number of dendritic trees =

Answer 34

more connections so may be responsible for higher sensitivity vision

Question 35

larger size of dendritic tree =

Answer 35

larger receptive field, not as good for high acquit vision. more suited for change within a large area

Question 36

properties of parvocellular ganglion cells

Answer 36

small field
sustained reponse
slow conduction velocity
low sensitive 
function to detect form/colour

Question 37

properties of magnocellular ganglion cells

Answer 37

large field
transient response
fast conduction velocity 
high sensitivity
function - motion detection