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Developing Nervous Systems > The visual system > Flashcards

The visual system Flashcards

1
Q

The visual system is tuned to recognise what three things?

A

Food
Predators
Mates

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2
Q

How does the optic nerve respond to light?

A

It increases or decreases the spike rates

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3
Q

The right hemifield activates what?

A

The left brain

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4
Q

What is the main function of the retina?

A

Image acquisition

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5
Q

What is the function of the geniculate nucleus?

A

It preprocesses the visual information and projects to the primary visual cortex

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6
Q

What is the function of the superior colliculosis?

A

Responsible for focusing the eye eg turning the head to see better

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7
Q

Where does the main processing of visual information occur?

A

The visual cortex

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8
Q

What are the two main pathways in the cortex and what do they do?

A

Ventral - ‘What?’ eg object recognition occurs in the inferior temporal part of the brain
Dorsal - ‘Where?’ spatial location occurs in the posterior parietal part

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9
Q

What is the role of the pupil?

A

It regulates the amount of light to fall on the retina

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10
Q

What is the role of the lens?

A

To focus images on the fovea

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11
Q

What is the fovea?

A

The part of the retina with the highest visual activity

The rest of the retina has smaller acuity and contains primarily rods

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12
Q

What does light travel through in the retina?

A

Muller cells - these span the whole of the retina

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13
Q

What is the basic layout of the retina?

A

There are three layers of neurons and 2 layers of synapses
Feedforward neurons include; photoreceptors, bipolar cells and ganglian cells
Feedback neurons are the horizontal and amacrine cells

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14
Q

What is the role of the role of the feedback neurons?

A

Horizontal and amacrine cells inhibit and feedback to the bipolar cells, they are GABA-ergic

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15
Q

When are rods active?

A

At dim light (cones are active in bright light)

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16
Q

Where does phototransduction occur in rod and cone cells?

A

The outer segment

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17
Q

How do photoreceptors respond to light flashes?

A

They hyperpolarise eg the membrane potential decreases

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18
Q

Describe the cascade that occurs in photoreceptors

A

At the end of the cascade channels are selctive for calcium and sodium - when these are open the membrane depolarises
These channels are open in DARKNESS
They are activated by cyclic GMP in the cytoplasm
Ligand gated g protein coupled receptors activate phosphodiesterase which decreases cGMP so the channels close and cells hyperpolarise in the presence of light

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19
Q

What are the properties of the photoreceptors synapses?

A

They have special ribbon synapses which are able to keep vesicle release permanently
They do not spike- they use graded potentials
They release glutamate = hyperpolarisation
When light increases the amount of glutamate released from the photoreceptors decreases

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20
Q

Where do bipolar and horizontal cells receive input from photoreceptors?

A

The outer plexiform layer

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21
Q

Where do gangloin cells and amacrine cells receive input from bipolar cells?

A

The inner plexiform layer

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22
Q

When do ON cells depolarise?

A

When light increases

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23
Q

OFF cells express which receptor?

A

Ionotropic glutamate receptor (excitatory)

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24
Q

ON cells express which receptor?

A

Metabotropic glutamate receptor (inhibitory)

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25
Q

What happens in the receptive field?

A

An area in the retina which when illuminated activates a visual neuron
Many visual neurons have centre surround organisation of the receptive field, meaning the illumination of the center and the surround leads to responses in opposite polarities

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26
Q

What are the main methods to study vision?

A 
Psychophysical methods and illusions
Lesions/ other ways to silence neurons
Anatomical studies and morphology
fMRI, electrophysiological recordings and imaging
Modeling and theoretical stimulations
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27
Q

What are the advantages and disadvantages of human models?

A

Good as the can give feedback

Bad as you need to use electrodes, unethical, long life span

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28
Q

Why are zebrafish brains good to use?

A

You can record the entire neurons of the whole brain

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29
Q

How can lesions occur?

A

They can be directed eg in animal models

They can occur after strokes or other neurodegenerate diseases

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30
Q

What is akinetopsia?

A

The inability to perceive motion

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31
Q

What is fMRI?

A

A way to study what areas of the brain are involved in visual processing
The parts being used are detected as they use a lot of glucose and oxygen due to their high activity
The subject looks at particular stimuli eg moving black dots to see what area of the brain responds

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32
Q

What are two ways of carrying out morphological studies?

A

Golgi staining for neurons - shows morphology of the ganglion cells
Fluorescent proteins labelled sparsely that express GFP - advantages is that it drives expression

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33
Q

What did Hubel and Weisel do?

A

They recorded from the visual area of the cat brain and gave it a visual stimulus like bars in different sizes and orientations
They used a sharp electrode to record spikes

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34
Q

What is GCaMP3 and how does it work?

A

Reports changes in neuronal calcium concentration, and therefore, neuronal activity
2 proteins CAM and MI3 fuse in the presence of calcium
If calcium is present in the cell they fuse and interact with GFP giving a ‘bright conformation’
Increase in the activity of neuron increases the brightness

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35
Q

What are the benefits of GCaMP3?

A

Many neurons can be recorded from
Simultaneously you can record an input and output
4 frames per second recorded
Particular neuron types can be recorded

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36
Q

What is channelrhodopsin?

A

Light activated channels causing sodium to move into the cell = depolarisation = spiking
Blue light = depolarisation

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37
Q

What is halorhodopsin?

A

Cause hyperpolarisation when activated by light (yellow light)

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38
Q

What is retinitis pigmentosa?

A

Most common cause of blindness
Currently there is no cure but progression can be slowed down
It causes major structural differences in the retina - photoreceptors are not present which causes the rest of the retina to degenerate and appear messy

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39
Q

Which parts of the brain can be stimulated to treat blindness?

A 
Retina (in retinitis pigmentosa)
Visual cortex (when the optic nerve is destroyed)
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40
Q

What are the problems with artificial retinal implants?

A

They stimulate retinal ganglion cells and not photoreceptors or bipolar cells

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41
Q

What is a receptive field?

A

An area in the retina (or space) which when illuminated activates a visual neuron

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42
Q

What is centre surround organisation?

A

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

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43
Q

Where do bipolar cells receive their input from?

A

Photoreceptors

44
Q

What is the effect of shining light on to the centre of an OFF bipolar cell’s receptive field?

A

The photoreceptors hyperpolarise which causes the bipolar cells to hyperpolarise

45
Q

What is the effect of shining light on to the surrounding of an OFF bipolar cell’s receptive field?

A

Photoreceptors hyperpolarise causing the horizontal cells to also hyperpolarise

46
Q

What do ganglion cell receptive fields have?

A

Center-surround organisation

47
Q

What is the difference between bipolar and ganglion cell receptive fields?

A

The ganglion cells respond with spikes

48
Q

How do OFF and ON center ganglion cells respond to light?

A

Off centre - respond with spikes if the surrounding receptive field is stimulated
On centre - respond with spikes if the centre is stimulated

49
Q

What happens if the whole of the ganglion cell receptor field is stimulated?

A

Cells do not usually respond as they receive inhbitory input from amacrine cells and excitatory input from the bipolar cells

50
Q

What are the two main classes of ganglion cells and what are their relevant percentages?

A

Parvocellular (80%) and magnocellular (10%)

51
Q

What are the differences between p and m ganglion cells?

A

p - midget (small field of dendrites), Sustained response, slow conduction velocity, low gain and sensitivity, function is for form and colour
m - parasol (large dendritic field), transient response, fast conduction velocity, high gain and sensitivity, function is for motion detection

52
Q

How many different types of bipolar cells are there?

A

15

53
Q

The position of bipolar cell stratification in the inner plexiform layer affects what?

A

The bipolar cells function
Projection to the top of the IPL = OFF cells
Projection to the bottom of the IPL = ON cells
It also affects if they are transient or sustained
Top part of IPL = transient
Bottom part of IPL = sustained

54
Q

Where do ON ganglion cells project to?

A

The bottom part of the inner plexiform layer

55
Q

How many types of amacrine cells are there?

A

50

56
Q

What is a flat mount retina?

A

Where a retina is taken and is cut so it is flat with the ganglion cells on top

57
Q

How can the morphology of the ganglion cell dendritic trees differ?

A

Size, density, diffuse, asymetric

58
Q

What are the key functions?

A 
Contrast adaptation and other forms of adaptation
Processing of colour
Processing of motion
Orientation reflex
Object recognition
59
Q

How is adaptation to temporal contrast measured?

A

Record from ganglion cells in flat mount retina
Patch clamp to measure spike rate
Increase in contrast causes an increase in the spiking rate which then decreases as a result of adaptation

60
Q

What are the two types of adaptation?

A

Depression

Facilitation

61
Q

What is depression?

A

Decrease in sensitivity

62
Q

What is facilitation?

A

Increase in sensitivity

63
Q

What should facilitation not be confused with and why?

A

Should not be confused with recovery
Facilitation = increase in sensitivity when stimulus increases
Recovery = increase in sensitivity when stimulus decreases

64
Q

Why do we need colour vision?

A

Helps with object recognition

65
Q

How many types of cones are there?

A

Blue, red and green

66
Q

Describe the distribution of cones in the retina and why they are distributed like this

A

The majority of green top of the retina because the grass is green and the image is flipped by the lens
The majority of the bottom has blue cones because the sky is blue

67
Q

Which type of ganglion cells have colour opponent properties

A

P cells

68
Q

What are colour opponent ganglion cells?

A

Cells that are tuned to respond to colour contrast eg if there is just green there is a small response but red and green gives a big response

69
Q

Damage to what part of the brain removes the ability to perceive motion?

A

The dorsal stream

70
Q

Where is direction selectivity prominent?

A

The retina

71
Q

How can the preferred direction of a direction selectivity cell be guessed?

A

From the morphology of the cells dendritic tree ie they are asymetric

72
Q

Which cells inhibit ganglion cells?

A

Amacrine cells

73
Q

What is the role of the fovea?

A

High visual acuity

74
Q

What is the orienting reflex?

A

Turning of the head and eyes so the stimulus is projected on the fovea

75
Q

What is smooth persuit?

A

Following a moving object

76
Q

What is a saccadic movement? Give an example

A

Eye movements as a result of inspection so the features project onto the fovea
The edges of the face, eyes, nose and mouth are the key features for recognition

77
Q

Ablation of what causes the loss of the orientation reflex in fish?

A

The optic tectum

78
Q

What is the optic tectum called in a lower verterbrate?

A

The superior colliculus

79
Q

Where does the superior colliculus receive its input from?

A

Ganglion cells, auditory system and somatosensory system

80
Q

What is the main function of the superior colliculus?

A

Saccadic movements

81
Q

What is a retinotopic map?

A

Organisation whereby neighboring cells in the retina feed information to the neighboring places in their target structures (LGN, SC, cortex)

82
Q

What does the foveation hypothesis state?

A

That interaction between these maps initiates orienting reflex

83
Q

Is the foveation map valid?

A

No because interaction between the maps seems to be indirect

84
Q

How many layers are there in the LGN?

A

6

85
Q

What are the contralateral layers of the LGN?

A

1, 4 and 6

86
Q

What are the ipsilateral layers if the LGN?

A

2, 3 and 5

87
Q

Which layers of the LGN contain p cells?

A

Layers 3 to 6

88
Q

How many ganglion cells connect with a LGN projection neuron

A

One

89
Q

What are the two visual pathways in the cortex?

A

The ventral pathway and the dorsal pathway

90
Q

What is the role of the dorsal pathway?

A

Motion detection

91
Q

What is the role of the ventral pathway?

A

Object recognition and colour

92
Q

What are the components of the ventral pathway?

A

V1 - V2 - V3 - medial temporial cortex

93
Q

What are the components of the dorsal pathway?

A

V1 - V2 - V4 - IT

94
Q

What is object invariance?

A

Large numbers of objects can be recognised in any orientation even if we haven’t seen that orientation before

95
Q

What is scale invariance?

A

Objects recognised independently of their size

96
Q

What is the heirarchal model of object recognition?

A

Detection of edges
Detection of combination of edges and contours
Detection of object parts
Detection of objects from one point of view
View invariant object recognition
Categorisation

97
Q

Where does the detection of edges occur?

A

V1 cortex

98
Q

Where does the detection of object parts occur?

A

The inferior temporal cortex

99
Q

What are the two structural features of the cortex?

A

Layering and columns

100
Q

What are the types of columns in the cortex?

A

Ocular dominance, orientation columns and blobs

101
Q

How can ocular dominance be seen in the visual cortex?

A

Injection of radioactive proline into one eye diffuses along the optic nerve, through the LGN and into the visual cortex - shows a stripe pattern
Or inject radioactive glucose and stimulate one eye with light

102
Q

What is the role of ocular dominance?

A

Helps for 3d vision

103
Q

What is the hypercolumn?

A

‘Blobs’
Columns which when labelled look like blobs
Contain neurons specifically tuned to process object and column information

104
Q

What are the three types of cell in the V1 cortex?

A

Simple, complex and hypercomplex

105
Q

When do simple cells spike?

A

When the bar is in a certain orientation in the centre of the visual field

106
Q

What is the simple cells receptive field like?

A

It is elongated

107
Q

How do complex cells differ from simple cells?

A

They respond to a bar of light in any orientation but anywhere in the receptive field

Developing Nervous Systems (11 decks)

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