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Neural Circuits > L4 - Visual System > Flashcards

L4 - Visual System Flashcards

1
Q

Visual system is tuned to recognise and localise which 3 stimuli?

A

Food
Predator
Mate

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2
Q

Morphology of a sensory neuron is largely defined by?

A

Its function

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3
Q

What are the 3 ways processing level is organised?

A

Positive feedforward
Negative feedback – horizontal cell back to photoreceptor
Negative feedforward

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4
Q

Which side of the brain does the right hemifield activate?

A

Left brain

Left hemifield activates right brain

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5
Q

What is the main function of the retina?

A

Image acquisition

Determines what is important for the brain to know

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6
Q

Where does the info from the eye go?

A

Goes to the LGN

Preprocess the visual information

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7
Q

Where does the info from the LGN go?

A

Goes to the primary cortex

Main processing of information

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8
Q

What are the two main visual pathways in the cortex?

A

Ventral

Dorsal

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9
Q

Ventral visual pathway

A

What
Object feature stream
Inferior temporal

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10
Q

Dorsal visual pathway

A

Where
Spatial location stream
Posterior parietal

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11
Q

What is the function of the pupil?

A

Regulates amount of light that falls on retina

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12
Q

What is the function of the lens?

A

Focuses image on the fovea

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13
Q

What is the function of the fovea?

A

Part of retina with highest visual acuity

Contains mainly cones

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14
Q

What is the function of the rest of the retina?

A

Smaller acuity
Contains mainly rods
Send signals to brain to help focus retina

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15
Q

What is the function of Muller cells?

A

Light travels through Muller cells

Helps guide the light through the tissue

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16
Q

What are the 3 feedforward neurons of the retina?

A
  1. Photoreceptors – pink
  2. Bipolar cells – blue
  3. Ganglion cells – purple
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17
Q

What are the 2 feedback neurons of the retina?

A
  1. Horizontal cells – yellow

2. Amacrine cells – orange

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18
Q

What is the function of amacrine cells?

A

Connect to ganglion and bipolar cells

Shapes way bipolar cells process info

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19
Q

What are the two layers of synapse in the retina?

A

Inner plexiform layer

Outer plexiform layer

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20
Q

What is the function f the inner plexiform layer?

A

Dense and complex structure
Contains synapses between bipolar, amacrine and ganglion
5-6 layers of synapses

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21
Q

Rods are active at?

A

Dim light

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22
Q

Cones are active at?

A

Bright light

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23
Q

How do photoreceptors respond to light flashes?

A

By hyperpolarisation

24
Q

Where does phototransduction occur?

A

In the outer segment

25
Which two proteins are involved in phototransduction?
Cyclic GMP | GMP
26
Membrane of photoreceptor cells contains?
Channels that transmit Na and Ca
27
Phototransduction in the dark method
The channels open and the membrane depolarises | Large concentration of cyclic GMP in cytoplasm
28
Phototransduction in the light method
A signal cascade involving G proteins G proteins activate phosphodiesterase Converts cyclic GMP to GMP reducing amount of cyclic GMP Channels close - hyperpolarisation of photoreceptor
29
Laminar retinal organisation
Bipolar and horizontal cells receive input from photoreceptors
30
Which bipolar cells hyperpolarise in response to light?
OFF cells
31
Which bipolar cells depolarise in response to light?
ON cells
32
What do photoreceptors release when depolarised by light?
Release glutamate
33
Sign inverting synapse in ON bipolar cells
On cells express metabotropic glutamate receptor – excitatory - Acts through G-protein cascade - Opens Na channels in membrane of bipolar cells
34
What do OFF bipolar cells express?
Ionotropic glutamate receptor - inhibitory
35
What do On bipolar cells express?
Metabotropic glutamate receptor – inhibitory
36
What is a receptive field?
An area in the retina which when illuminated activates a visual neuron
37
Centre-surround organisation of bipolar cell receptive field
Many visual neurons have center-surround organisation of the receptive field - Illumination of the center leads to responses in opposite polarities
38
Activation of bipolar cells with spot and annulus of light leads to?
Responses with different polarities
39
Many photoreceptors converge?
To one bipolar cell
40
Mechanism of centre-surround organization of bipolar cells?
Some photoreceptors - Activate directly - Activate via horizontal cells
41
Photoreceptors that activate directly are found?
In the centre | Cause cell to hyperpolarise
42
Photoreceptors that activate via horizontal cells are found?
In the surround | Cause cell to depolarise - inhibitory
43
IPL contains which 3 synapses of bipolar cells?
Axons of ON bipolar cells Dendrites of ON ganglion cells Dendrites of ON amacrine cells
44
Morphology of ganglion cells dendritic trees
Ganglion cells have diverse but distinct morphology of the dendritic trees - Size - Symmetry - Denseness
45
Ganglion cells receptive fields have?
Centre-surround organisation
46
Does illumination of the whole receptive field activate ganglion cells?
No
47
Ganglion cells respond to differences in?
Illumination that occur within the receptive field
48
What happens if you stimulate centre of ganglion cells?
Increase rate of spiking – on cell | Complete stop of spiking – off cell
49
What happens if you stimulate surround of ganglion cells?
Complete stop of spiking – on cell | Increase rate of spiking – off cell
50
What happens if you stimulate the whole receptive field of ganglion cells?
No difference in response
51
What are the two classes of ganglion cells?
Parvocellular (80%) | Magnocellular (10%)
52
Magnocellular characteristics
``` Large dendritic tree Transient response Fast conduction velocity High sensitivity Function - detect motion ```
53
Parvocellular characteristics
``` Small dendritic tree Sustained response Slow conduction velocity Low sensitivity Function – processing info about shape and colour ```
54
What is adaptation?
Decrease in activity | Often reasons for visual illusions
55
What is sensitisation?
Increase in activity

Neural Circuits (15 decks)

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