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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
Q

Which two proteins are involved in phototransduction?

A

Cyclic GMP

GMP

26
Q

Membrane of photoreceptor cells contains?

A

Channels that transmit Na and Ca

27
Q

Phototransduction in the dark method

A

The channels open and the membrane depolarises

Large concentration of cyclic GMP in cytoplasm

28
Q

Phototransduction in the light method

A

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
Q

Laminar retinal organisation

A

Bipolar and horizontal cells receive input from photoreceptors

30
Q

Which bipolar cells hyperpolarise in response to light?

A

OFF cells

31
Q

Which bipolar cells depolarise in response to light?

A

ON cells

32
Q

What do photoreceptors release when depolarised by light?

A

Release glutamate

33
Q

Sign inverting synapse in ON bipolar cells

A

On cells express metabotropic glutamate receptor – excitatory

  • Acts through G-protein cascade
  • Opens Na channels in membrane of bipolar cells
34
Q

What do OFF bipolar cells express?

A

Ionotropic glutamate receptor - inhibitory

35
Q

What do On bipolar cells express?

A

Metabotropic glutamate receptor – inhibitory

36
Q

What is a receptive field?

A

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

37
Q

Centre-surround organisation of bipolar cell receptive field

A

Many visual neurons have center-surround organisation of the receptive field
- Illumination of the center leads to responses in opposite polarities

38
Q

Activation of bipolar cells with spot and annulus of light leads to?

A

Responses with different polarities

39
Q

Many photoreceptors converge?

A

To one bipolar cell

40
Q

Mechanism of centre-surround organization of bipolar cells?

A

Some photoreceptors

  • Activate directly
  • Activate via horizontal cells
41
Q

Photoreceptors that activate directly are found?

A

In the centre

Cause cell to hyperpolarise

42
Q

Photoreceptors that activate via horizontal cells are found?

A

In the surround

Cause cell to depolarise - inhibitory

43
Q

IPL contains which 3 synapses of bipolar cells?

A

Axons of ON bipolar cells
Dendrites of ON ganglion cells
Dendrites of ON amacrine cells

44
Q

Morphology of ganglion cells dendritic trees

A

Ganglion cells have diverse but distinct morphology of the dendritic trees

  • Size
  • Symmetry
  • Denseness
45
Q

Ganglion cells receptive fields have?

A

Centre-surround organisation

46
Q

Does illumination of the whole receptive field activate ganglion cells?

A

No

47
Q

Ganglion cells respond to differences in?

A

Illumination that occur within the receptive field

48
Q

What happens if you stimulate centre of ganglion cells?

A

Increase rate of spiking – on cell

Complete stop of spiking – off cell

49
Q

What happens if you stimulate surround of ganglion cells?

A

Complete stop of spiking – on cell

Increase rate of spiking – off cell

50
Q

What happens if you stimulate the whole receptive field of ganglion cells?

A

No difference in response

51
Q

What are the two classes of ganglion cells?

A

Parvocellular (80%)

Magnocellular (10%)

52
Q

Magnocellular characteristics

A 
Large dendritic tree 
Transient response 
Fast conduction velocity 
High sensitivity 
Function - detect motion
53
Q

Parvocellular characteristics

A 
Small dendritic tree 
Sustained response 
Slow conduction velocity 
Low sensitivity 
Function – processing info about shape and colour
54
Q

What is adaptation?

A

Decrease in activity

Often reasons for visual illusions

55
Q

What is sensitisation?

A

Increase in activity

Neural Circuits (15 decks)

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