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Physiology and Neuroscience Semester 2 > The visual system > Flashcards

The visual system Flashcards

1
Q

What does the retina contain?

A

Photoreceptors

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2
Q

What do photoreceptors do?

A

Convert light to changes in membrane potential

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3
Q

What is the output of the retina via?

A

Ganglion cells

Axons in the optic nerve

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4
Q

What do bipolar cells do?

A

Link photoreceptors to ganglion cells

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5
Q

What do horizontal cells do?

A

Mediate lateral interactions

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6
Q

What are the two types of photoreceptors in the retina?

A

Rods

Cones

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7
Q

What are cones?

A

Less sensitive than rods

Operate optimally in daylight

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8
Q

What are rods?

A

More sensitive than cones (x1000)
Operate optimally in low light levels (twilight)
Saturated in daylight

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9
Q

Where are cones?

A

Concentrated at the fovea

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10
Q

Where are rods?

A

More numerous in the peripheral retina

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11
Q

What do rods and cones differ in?

A

Connectivity
Sensitivity
Distribution

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12
Q

What do cones connect?

A

1 to 1 with bipolar and ganglion cells

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13
Q

What do rods converge on?

A

Ganglion cells

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14
Q

How many types of cones does the retina contain?

A

3 types

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15
Q

What are these types of cones?

A

Maximally sensitive to a different wave length of light
Blue cones
Green cones
Red cones

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16
Q

What is the trichromacy theory?

A

The colour we perceive is largely determined by the relative activation of blue, green and red cones

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17
Q

What can be used to test for red-green colour-blindness?

A

Ishihara’s cards

Confusion of shades of red and green

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18
Q

How many people have red-green colour-blindness?

A

2% of the male population

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19
Q

What is missing in individuals with red-green colour-blindness?

A

Cones sensitive to red light are missing

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20
Q

What is a receptor field?

A

Area of retina it receives input

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21
Q

What is on centre retinal ganglion?

A

Light is stimulus that excites them

22
Q

What is the off centre retinal ganglion?

A

Stimulated by shadow

23
Q

How are ganglion cells organised?

A

Concentric centre surround (excitatory-inhibitory) receptive field organisation

24
Q

What is the illumination responses to stimulation in the centre cancelled by?

A

The response to stimulation in the surround

25
Q

What are maximum response to in luminance contrast?

A

Light-dark boundaries

26
Q

How many M type cells are involved in luminance contrast?

A

10%

27
Q

How many P type cells are there?

A

90%

28
Q

What are P type cells sensitive to?

A

Different wavelengths

29
Q

What do colour-opponent centre surround receptive fields respond to?

A

Light of one wavelength in the centre is cancelled by light of another wavelength in the suround

30
Q

What colour pairs cancel?

A

Red-green

Blue-yellow

31
Q

Where do the optic nerves of each eye join?

A

Optic chiasm

32
Q

Where do fibres from the nasal retina meet?

A

Both eyes cross (partial decussation)

Cross at the optic chiasm

33
Q

What do optic tracts carry information about?

A

Info relating to visual hemisfield

34
Q

Where do optic tracts project on to?

A

Lateral genicualte nucleus (LGN) of the thalamus

35
Q

What does the LGN consist of?

A

6 layers

36
Q

What types of cells are in the LGN?

A

M-type and P-type

37
Q

Where do M and P cells project?

A

M- magnocellular layers (1 and 2)

P- parvocellular layers (3-6)

38
Q

What are the receptive field properties of the LGN neurones similar to?

A

Ganglion cells

39
Q

What are LGN neurones primarily?

A

A relay to the cortex- information from different ganglion cells and different eyes is carried by segregated parallel lines

40
Q

Where do thalamic relay neurones from the LGN terminate?

A

Layer IV of primary visual cortex

41
Q

Where does information from 2 eyes project?

A

Alternating bands called ocular dominance columns

42
Q

What do simple cells show?

A

Orientation selectivity

43
Q

What are the different cortical areas that are specialised for different visual processing tasks?

A

V1
V5
V4

44
Q

What does the V1 do?

A

Parcels out information to other specialised areas of cortex

45
Q

Where do thalamic neurones terminate in V1?

A

Layer IV

46
Q

What are cortical neurones like in V1?

A

More elaborate receptive fields- several relay neurones feed into them

47
Q

What does V1 also extract?

A

Additional information

E.g. orientation, selectivity, direction selectivity

48
Q

What does V1 parcel out?

A

Visual information to other specialised ares of the cortex

49
Q

What is V5 specialised for?

A

Motion analysis- stimulated by viewing a moving pattern of black and white squares

50
Q

What do lesions of V5 lead to?

A

Akinetopsia

Can’t see objects if they move

51
Q

What is V4 specialised for?

A

Colour vision- stimulated by viewing an abstract pattern of colours

52
Q

What do lesions of V4 lead to?

A

Achromotopsia

See only in shades of grey

Physiology and Neuroscience Semester 2 (20 decks)

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