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Physiology and Neuroscience > Vision > Flashcards

Flashcards in Vision Deck (52):
1

What does the retina contain?

Photoreceptors

2

What do photoreceptors do?

Convert light to changes in membrane potential

3

What is the output of the retina via?

Ganglion cells
Axons in the optic nerve

4

What do bipolar cells do?

Link photoreceptors to ganglion cells

5

What do horizontal cells do?

Mediate lateral interactions

6

What are the two types of photoreceptors in the retina?

Rods
Cones

7

What are cones?

Less sensitive than rods
Operate optimally in daylight

8

What are rods?

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

9

Where are cones?

Concentrated at the fovea

10

Where are rods?

More numerous in the peripheral retina

11

What do rods and cones differ in?

Connectivity
Sensitivity
Distribution

12

What do cones connect?

1 to 1 with bipolar and ganglion cells

13

What do rods converge on?

Ganglion cells

14

How many types of cones does the retina contain?

3 types

15

What are these types of cones?

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

16

What is the trichromacy theory?

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

17

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

Ishihara's cards
Confusion of shades of red and green

18

How many people have red-green colour-blindness?

2% of the male population

19

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

Cones sensitive to red light are missing

20

What is a receptor field?

Area of retina it receives input

21

What is on centre retinal ganglion?

Light is stimulus that excites them

22

What is the off centre retinal ganglion?

Stimulated by shadow

23

How are ganglion cells organised?

Concentric centre surround (excitatory-inhibitory) receptive field organisation

24

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

The response to stimulation in the surround

25

What are maximum response to in luminance contrast?

Light-dark boundaries

26

How many M type cells are involved in luminance contrast?

10%

27

How many P type cells are there?

90%

28

What are P type cells sensitive to?

Different wavelengths

29

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

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

30

What colour pairs cancel?

Red-green
Blue-yellow

31

Where do the optic nerves of each eye join?

Optic chiasm

32

Where do fibres from the nasal retina meet?

Both eyes cross (partial decussation)
Cross at the optic chiasm

33

What do optic tracts carry information about?

Info relating to visual hemisfield

34

Where do optic tracts project on to?

Lateral genicualte nucleus (LGN) of the thalamus

35

What does the LGN consist of?

6 layers

36

What types of cells are in the LGN?

M-type and P-type

37

Where do M and P cells project?

M- magnocellular layers (1 and 2)
P- parvocellular layers (3-6)

38

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

Ganglion cells

39

What are LGN neurones primarily?

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

40

Where do thalamic relay neurones from the LGN terminate?

Layer IV of primary visual cortex

41

Where does information from 2 eyes project?

Alternating bands called ocular dominance columns

42

What do simple cells show?

Orientation selectivity

43

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

V1
V5
V4

44

What does the V1 do?

Parcels out information to other specialised areas of cortex

45

Where do thalamic neurones terminate in V1?

Layer IV

46

What are cortical neurones like in V1?

More elaborate receptive fields- several relay neurones feed into them

47

What does V1 also extract?

Additional information
E.g. orientation, selectivity, direction selectivity

48

What does V1 parcel out?

Visual information to other specialised ares of the cortex

49

What is V5 specialised for?

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

50

What do lesions of V5 lead to?

Akinetopsia
Can't see objects if they move

51

What is V4 specialised for?

Colour vision- stimulated by viewing an abstract pattern of colours

52

What do lesions of V4 lead to?

Achromotopsia
See only in shades of grey