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Sem 3 Neuro > Vision > Flashcards

Vision Flashcards

1
Q

What is the central part of vision?

A

→ Fovea

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2
Q

Where is aqueous humour produced?

A

→ Ciliary body

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3
Q

What is the function of aqueous humour?

A

→ keeps the vitreous humour hydrated

→ maintains enough pressure to keep the eye rigid

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4
Q

What is glaucoma caused by?

A

→ too much pressure

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5
Q

What do the suspensory ligaments do?

A

→ suspend the lens

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6
Q

What is the function of the ciliary muscles?

A

→ They make the lens more convex or concave

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7
Q

What is the function of the iris?

A

→ Controls the size of the central pupil

→ controls how much light enters the eye

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8
Q

What is the function of the lens?

A

→ fine focus

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9
Q

What does the pupil do?

A

→ cut our the light rays that would otherwise go through the edge of the lens

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10
Q

Where is the neural retina generated from?

A

→ The neural tube

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11
Q

What does the neural retina contain?

A

→ Neural circuit which links photoreceptors to retinal ganglion cells

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12
Q

What takes the signal to the brain?

A

→ Retinal ganglions have axons that join with the optic nerve and take the signal to the brain

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13
Q

Describe the pathway to the brain from the eyes

A

→ Axons project back via the optic nerve
→ the two nerves meet at the optic chiasm and some axons swap over
→ they run into the optic tract which goes up into the brain
→ the main branch goes to the lateral geniculate nucleus
→ they activate relay cells that carry the signal to the primary visual cortex
→they run in the subcortical white matter known as the optic radiation

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14
Q

Where is the visual cortex?

A

→ occipital lobe

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15
Q

What are rods used for?

A

→ night vision

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16
Q

What are cones used for?

A

→ high light levels

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17
Q

What does the synaptic terminal release in cones?

A

→ Glutamate

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18
Q

What is the outer segment of cones made from?

A

→ Layers of membranes

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19
Q

What is the ordinary resting potential of cone cells?

A

→ -45mv

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20
Q

What is the resting potential of nerve cells?

A

→ -70mv

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21
Q

What channels do cones have?

A

→ Na+ in the outer segment that leak Na+ inwards

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22
Q

Describe the phototransduction cascade

A

→ Guanylyl cyclase converts GTP to cGMP
→ cGMP receptors are on Na+ channels which allows Na+ in so the inside of the cell is +ve
→ When light hits rhodopsin cis retinal changes to all trans retinal which frees opsin
→ opsin activates transducin which activates phosphodiesterase
→ PDE breaks down cGMP
→cGMP can’t bind to the channels so they close and the cell hyperpolarises - very little action potentials
→ Less action potentials means less calcium near the synaptic terminal and less glutamate release
→ very little glutamate release stimulates the bipolar neurons

23
Q

Describe how adaptation works?

A

→ Phototransduction cascade amplifies the response to each photon so it produces a rapid change in membrane potential
→ when the light is stable for a few seconds the receptor changes its sensitivity and shifts the membrane back down to resting

24
Q

What are photoreceptors telling us?

A

→ brightness over a particular area of the retina has changed

25
Q

What can loss of peripheral vision be due to?

A

→ Glaucoma

→ Retinitis pigmentosa

26
Q

What can loss of central vision be related to?

A

→ Age-related macular degeneration

27
Q

How do photoreceptors communicate?

A

→ bipolar cells to ganglion cells

28
Q

Why is the image blurry?

A

→ Light rays are going to be diffused as they pass through to get to the end of the photoreceptors

29
Q

What is convergence?

A

→ Bipolar cells gather information from multiple photoreceptors before passing it on to ganglions

30
Q

Where do the nerves converge?

A

→ The optic nerve head

31
Q

What is the foveal region?

A

→ A region where all the retina apart from the photoreceptors have been pushed to one side

32
Q

What types of photoreceptors are in the foveal region?

A

→ Only red and green

33
Q

How do ganglions receive signals in the central part of the retina?

A

→ They do not converge

→ they receive signals from a single photoreceptor each

34
Q

What are the 3 properties of peripheral vision?

A

→ visual image is blurred
→ cone receptors are large and widely spread
→ signals from many cones converge onto single ganglion cells

35
Q

What are the 4 properties of central vision?

A

→ Good focus
→ only cone photoreceptors - red and green
→ narrow and closely packed
→ signals from the photoreceptors are kept separate through the primary visual pathway

36
Q

What is the fovea specialised for?

A

→ High resolution

37
Q

Where is information from ganglion cells sent?

A

→ Back via the optic nerve to the lateral geniculate nucleus
→ to the occipital cortex

38
Q

What happens to the image as it is passed through the optics?

A

→ inverted

39
Q

What sides of the retina crossover?

A

→ the nasal sides

40
Q

Where do the right side of both retinae project to?

A

→ The right side of the two retinae end up on the right side of the visual cortex

41
Q

What map do axons form?

A

→ Retinoptic map
→ maps for the two eyes on both sides of the brain
→ right sides of two retinae on right side of the cortex and the left side of the two retinae are on the left side of the cortex

42
Q

What types of cones are in the fovea and what types of cones are everywhere else (color)?

A

→ Red and green and blue everywhere else

→ red and green in the fovea

43
Q

Describe how receptive fields work in an on center off surround situation

A

→ The center cone is hyperpolarised because it is illuminated
→ it releases very little glutamate
→ the surround cones are depolarised because they are not illuminated
→ they release a lot of glutamate
→ The horizontal cell is stimulated by the glutamate
→ it sends inhibitory feedback to all the cones
→ it causes the center cone to release even less NT
→ which excites the bipolar cell even more

44
Q

Describe how receptive fields work in an on surround, on center situation

A

→ All cones are hyperpolarised as all of them are illuminated
→ the horizontal cell is minimally excited and inhibition is reduced
→ they release a lot of NT
→ so the bipolar cell is less excited

45
Q

Describe how receptive fields work in an on surround, off center situation

A

→ The outer cones are hyperpolarised as they are illuminated
→ the center cone is depolarised as it is not illuminated
→the horizontal cell is minimally excited and inhibition is reduced
→ the center cone is already depolarised and the inhibition is reduced so it depolarises even more and releases a lot of NT
→ this leads to the bipolar cell being the least excited

46
Q

What is the relationship between horizontal cells and the number of cones?

A

→ The more cones send a +ve signal to the horizontal cells

→ the less inhibition the horizontal cell sends

47
Q

What are parvocellular neurons good at doing?

A

→ Responding to fast moving things or fine detail

48
Q

What are magnocellular neurons good at doing?

A

→ Responding to coarse detail

49
Q

How can photoreceptors distinguish color?

A

→ compare inputs from red and green

→ compare inputs from blue and red+green (yellow)

50
Q

What do laternal geniculate cell inputs look like?

A

→ same as the retinal inputs

→ faithful relay cells

51
Q

What happens in primary visual cortical cells?

A

→ receptor fields converge information from different parts of the retina
→ respond in an orientation specific way

52
Q

What does the infratemporal area deal with and with what cells?

A

→ Recognition of the object including color

→ parvocellular areas

53
Q

What does the parietal cortex deal with and with what cells?

A

→ Deals with recognising movement and location of things

→ magnocellular cells

Sem 3 Neuro (21 decks)

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