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Foundations of Neuroscience > Vision > Flashcards

Flashcards in Vision Deck (66):
1

Where is the vitreous humour?

Behind the lens

2

What is the vitreous humour?

Jelly like substance
Necessary for structural stability

3

Where is aqueous humour?

Behind the cornea

4

What does the aqueous humour do?

Deliver nutrients to the cornea

5

Where is aqueous humour made?

Posterior chamber (behind the iris)

6

Where is aqueous humour reabsorbed?

Anterior chamber

7

Where does refraction occur?

Cornea
Lens

8

What is accommodation?

Adjusting the thickness of the lens

9

What controls the thickness of the lens?

The ciliary muscles

10

What connects the lens to the ciliary muscle?

Zonule fibres

11

How does the lens thicken?

Ciliary muscle constricts
Zonule fibres relax
Lens has natural elasticity

12

When does the lens thicken or thin?

Near objects = thin
Far objects = thicken

13

How does the lens thin?

Ciliary muscle relaxes
Zonule fibres tense
Lens thinned

14

What nervous system controls the muscles of the eye?

The autonomic nervous system

15

Besides the ciliary muscle, where else are there muscles in the eye?

Around the pupil

16

Name the two types of photoreceptor

Rods
Cones

17

What connects the cells of the retina?

Chemical synapses

18

What generates action potentials in the eye?

Ganglion cells

19

What allows lateral transmission?

Horizontal cells
Amacrine cells

20

Name the three structural parts of photoreceptors

Outer segment
Inner segment
Synaptic terminals

21

Where are photopigments located?

Outer segment

22

What is the name of the photopigment in rods?

Rhodopsin

23

What are photopigments specific to?

Wavelength of light

24

Where is rhodopsin found?

Intracellular disks

25

How sensitive are rods? Why?

Very
High density of intracellular disks
High levels of rhodopsin
High surface area

26

How many photopigments are there in cones?

3

27

What are the three photopigments in cones?

Red opsin
Blue opsin
Green opsin

28

Where are the opsins found?

Infoldings of surface membrane

29

How sensitive are cones? Why?

Not very
Low surface area
Low levels of opsins

30

Which photoreceptor is responsible for colour vision?

Cones

31

What is the blind spot?

Where neurones enter the fovea and there are no photoreceptors

32

Explain the distribution of cones and rods across the retina

Fovea = all cones
Periphery = majority rods

33

Is the periphery sensitive?

Very
High number of rods
Rods are very sensitive
A lot of convergence of rods to ganglion cells

34

What is low visual acuity? Why is there low visual acuity at the periphery?

Low clarity of vision
Convergence of rods means detail is lost

35

What is the macula?

The centre of the retina

36

How sensitive is the fovea?

Not very
Low sensitivity of cones
1 cone: 1 gangion cell

37

What happens to other cells in the fovea?

Lateral displacement
Allows as much light as possible to reach photoreceptors

38

What is high acuity? Why is there high acuity at the fovea?

High clarity of vision
1 cone: 1 ganglion
Many separate signals
Detail not lost

39

What is rhodopsin made up of?

Retinal (chromophore)
Opsin (G protein coupled receptor)

40

In the dark, what is happening in a rod cell?

Rhodopsin is inactive
cyclicGMP-gated cation channels are open
Na+ enters the rod cell

41

What is the flow of Na+ called?

The dark current

42

What is the resting membrane potential of a rod cell in the dark?

-30mV

43

Is the cell depolarised in the dark?

Yes

44

What happens at the synapse in the dark?

Glutamate is released

45

When light hits a rod cell, what absorbs the light?

Retinal

46

What conformation change happens to retinal?

Changes from 11-cis to all-trans

47

What does the change in retinal trigger?

Opsin is activated

48

What happens once optin is activated?

GTP binds to the G-protein

49

What does the G-protein activate?

Phosphodiesterase

50

What does phosphodiesterase do?

Breaks down cyclicGMP
Channel closes

51

Why does the cell hyperpolarise?

The Na+ channels close
Leak channels for K+ remain open

52

What happens at the synapse in the light?

Glutamate release stops

53

What is the route of transmission through the retina?

Photoreceptor
Bipolar cell
Ganglion cell

54

What do photoreceptors do in the light?

Hyperpolarise

55

What are the two classifications of bipolar cells?

On
Off

56

What do on bipolar cells do in the light and in the dark?

Depolarised by light
In the dark the glutamate from the photoreceptor hyperpolarises them
In the light the lack of glutamate depolarises them

57

What do off bipolar cells do in the light and in the dark?

Hyperpolarised by light
In the dark, glutamate depolarises them
In the light, lack of glutamate hyperpolarises them

58

What causes opposite actions of bipolar cells?

The receptors they possess

59

Name the two classes of ganglion cell

On and off

60

For both ganglion cells and bipolar cells. Summarise on and off

On = depolarised by light
Off = hyperpolarised by light

61

What is the receptive field?

The region of the retina that influences a bipolar or ganglion cell

62

What are the two divisions of the receptive field?

Central part
Surround part

63

What is in the central part?

Direct connections from photoreceptors

64

What is the surround part?

Lateral transmission of information via either horizontal or amacrine cells

65

What happens when light is present in the surround field?

The opposite electrical response in bipolar and ganglion cells

66

Why is the input of the surround field necessary?

Helps create contrast in image