Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Neurology > Vision > Flashcards

Vision Flashcards

1
Q

What is the role of the eye?

A

The eye captures an image of the world

It needs the ability to focus the image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Outline the two distinctive regions used to navigate around the eye

A

From above can split eye into temporal and nasal half (named after temporal bone and the nose)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Explain where the temporal field focuses along the retina?

A

Temporal visual field focuses on the nasal part of the retina and vice versa because the optics of the eye inverse the image and flip it top to bottom. (top part of the world is focused onto the bottom of the retina etc.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe the structure of the outer fibrous layer of the eye

A

Non-stretchy sclera acts as the anchoring point for the extraocular eye muscles that move the eye around.

The collagen fibres and cells at the front of the eye, align so that its a transparent layer to form the cornea.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Explain how the inner layers of the eye are kept rigid and stable

A

Non-stretchy sclera is flexible so allows the intraocular pressure keeps eye rigid, back surface smooth and stable, and distances between optics and retina correct

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is the intraocular pressure generated?

A

Intraocular pressure is generated by the aqueous humour (fluid that fills the eye). It’s produced by the ciliary body and is pushed outwards and reabsorbed by the angle of the eye. - v. slow flow

Balanced production and drainage of aqueous humour produces enough pressure to hold the eye rigid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is vitreous humour?

A

Vitreous humour is a jelly like structure behind the lens. It is hydrated by the aqueous humour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does the vitreous humour change with age?

A

As you get older, the proteins within vitreous become clumped leaving watery patches. This causes the vitreous to pull away from the back of the eye, causing it to shrink => can cause visual problems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the optic structures of the eye?

A 
Cornea
Lens
Ciliary Body
Iris
Pupil
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the role of the cornea and lens?

A

Cornea and lens bend light rays.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How odes cornea bend light entering the eye?

A

Cornea is the most powerful refractory surface in our eye, due to its curvature. As light touches water surface of cornea, it bends inwards

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Where is the lens located in the eye?

A

Lens sits behind cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the structure of the lens

A

Transparent and can change shape to alter focus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How is the lens suspended?

A

Lens is suspended by a ring of suspensory ligaments from the ciliary body

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How does the lens change shape to alter focus?

A

Ciliary body contains a ring of muscle which changes the shape of the lens

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Explain how muscle contraction changes lens size

A

When muscle contracts, muscle diameter reduces, lens = fatter

When the ring of muscle relaxes, muscle diameter is wider, lens is thinner

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the iris of the eye?

A

Iris is a ring of muscle that creates the coloured part of the eye

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the function of the iris?

A

Produces aperture in the middle which can close down to adapt to different light conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How does the pupil respond to light?

A

Pupil expands in dim light, narrows in bright light - due to retina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is the significance of a small lens aperture?

A

Pupil maintains the smallest aperture possible for the illumination conditions as the smaller the aperture = better focus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

When looking at a single point, where is the light reflected from?

A

Looking at a single point in visual space reflects light off in all directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe what happens to the light reflecting off from a point?

A

Some rays strike the cornea and pass through
Some rays stopped by the iris

Those that pass through the pupil will be brought back to focus as a single point by the lens and cornea

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Why are light rays converged?

A

The diverging light rays are bent to converge them to a single point to focus the image

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

How does a smaller pupil allow better focus?

A

Light passing through the edges of the lens won’t be focused accurately - smaller pupil = more accurate focus => better depth of field
This is because the lens has a great deal of optical aberrations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Where is the image being seen, focused?

A

Image is focused to the back of the eye => retina

Image blurs as passes through retinal tissue; scattered

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Once focused to the retina, how do we see an image?

A

The eye transmits the image to the visual cortex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Describe the structure of the retina

A

Neural retina is the innermost layer

Retinal pigment epithelium outer layer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Why are the retinal pigment epithelium and the retina CNS structures?

A

Retinal pigment epithelium is a part of the retina and developed embryonically from the neural tube as was the retina
=> both CNS structures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the role of the retinal pigment epithelium?

A

provides biochemical support for photoreceptors, and holds the retina in place, prevents it from peeling away

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Describe the structure of the optic nerve

A

Optic nerve is a CNS tract although it is referred to a nerve due to its shape
CNS tracts and peripheral nerves are myelinated by different types of glial cells

Optic nerve myelinated by oligodendrocytes as it is a tract

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Which disorder is associated with the optic nerve degradation?

A

Multiple sclerosis initial symptoms involve problems with the optic nerve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is the purpose of the neural retina?

A

Neural retina contains photoreceptors and afferents (retinal ganglion cells)

Retinal ganglion cells axons run across the surface of the retina and go on to form the optic nerve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Outline the primary visual pathway

A
  1. Ganglion cell axons project down the optic nerve to the
    optic chiasm.
  2. Ganglion cells on the nasal side of the retina swap sides
    at the chiasm, temporal side cells remain the same side.
  3. Ganglion cells project back to the LGN (lateral
    geniculate nucleus) - specific nucleus in thalamus that
    serves the visual system
  4. LGN cells send their axons through the optic radiation
    (region of white matter), to the occipital cortex (primary
    visual area)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

How is subconscious eye movement achieved?

A

Some of these axons form branches towards the brainstem, where they innervate different nuclei involved in subconscious activities e.g. subconscious eye movement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

When are the different photoreceptors active?

A

Rod Photoreceptors: night vision

Cone photoreceptors: day vision

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

How do the two types of photoreceptors work?

A

Two types of cone cells are two different systems, but use the same neural circuits once light hits the retina → brain
But before retina either rods or cones and their respected neural circuits are activated

37
Q

What structures are found in the inner segment of cone receptors?

A
  • nucleus
  • protein making machinary
  • axon (doesn’t fire action potentials)
  • synaptic terminal
38
Q

Explain why action potentials aren’t required in cone cells?

A

Uses electrotonic potentials to transmit info from one end to another - doesn’t need action potentials as its a small structure

39
Q

Which neurotransmitter is released at cone cell synaptic terminals?

A

Cone receptors have a synaptic terminal that release glutamate (excitatory neurotransmitter)

40
Q

How is glutamate release regulated in cone cells?

A

Glutamate release mediated by transduction apparatus in the outer segment

41
Q

Describe the structure of the outer segment of cone cells

A

Outer segment is a bag containing tiny packed infolding of phospholipid membranes layers - these hold the chromophore (light sensitive area) in neat layers, perpendicular to the light path - ensures efficient trapping of the light rays

42
Q

What effect doe slight have on cone cells during the day?

A

During the day light is hyperpolarizing in cone cells

43
Q

Outline the resting membrane potential of a cone cell compared to a typical neuron

A

Typical nerve cell RMP = -70mV

Typical cone cell RMP = -45mV

44
Q

Why do cone cells have a more positive RMP than typical nerve cells?

A

Cone cells are therefore depolarised even at rest - due to Na+ channels being open by default in outer segment

45
Q

How doe slight hyperpolarise cone cells?

A

When brighter light strikes the cone cell outer segment, some of the Na+ channels will close - cell becomes more negative - prevents some glutamate release.

46
Q

How do cone receptors respond to decreased light?

A

As outer segment region gets darker, more Na+ channels open

=> cell depolarises causing more glutamate to be released

47
Q

Why are cone cells so effective at responding to change sin light?

A

The biochemical cascade supports a very rapid response to changes in illumination

48
Q

What allows the Na+ channels to remain open during the RMP in cone cells?

A

Na+ channel held open by intracellular messenger, cGMP

49
Q

What is the chromophoric component of cone cells composed of?

A

Photo pigment composed of opsin protein and retinal (11-cis retinaldehyde) which is the chromophore

50
Q

Describe the structure of 11-cis retinaldehyde

A

11-cis retinal composed of a C ring and C tail

All C-C links forming the C tail are in the trans formation apart from C11 which is in cis formation => 11-cis retinal

51
Q

Explain how the 11-cis retinaldehyde initiates the response to light in cone cells

A

The cis configuration is less stable than the trans formation

When light strikes the molecule, the unstable cis bond to rupture, and reform in the more stable trans configuration of all-trans retinaldehyde

Opsin is now activated photopigment → acts in the same way an activated G coupled protein would

52
Q

What is the effects of activated opsin?

A

Activated opsin photopigment activates many G proteins ⇒ activate enzymes which destroy cGMP

Descreased [cGMP]i
⇒ cGMP moves away from Na+ channels allowing them to close

53
Q

How is the light response terminated?

A

The cascade is terminated at several levels, including the phosphorylation of rhodopsin by rhodopsin kinase, the subsequent binding of phosphorylated rhodopsin by arrestin

54
Q

What effect does termination of the light response have?

A

→ removes activated retinal
→ deactivates G proteins
→ stops enzymatic cGMP removal

Allows build up of [cGMP]i to be restored
⇒ reopens Na+ channels

55
Q

Explain how retinal processing occurs

A

You can only see in detail with the very centre of your visual field; small thumbnail of retina

56
Q

Name disorders leading to loss of peripheral vision

A

Loss of peripheral vision:

E.g. Glaucoma, retinitis pigmentosa

57
Q

Which disorders may cause a loss in central vision?

A

Age -related macular degeneration - destroys retina; lose ability to see detail

58
Q

What is the role of the inter-neuron circuitry?

A

Interneuron circuitry extracts detail from the photoreceptor signals and transmits it to the ganglion cells

59
Q

Why are we only able to see fine detail through the centre of the retina?

A

Cone photoreceptors in periphery are separated by pools of rod cells - cone cells concentrated at retina
← large gaps on sampling array in peripheral retina

60
Q

Why is the peripheral retina not able to see as much detail?

A

Ganglion cells receive input from the photoreceptors via bipolar cells
Bipolar cells pick up info from a pool of receptors (not just one) ⇒ convergence’ increases pixel size

61
Q

What is the receptive field centre?

A

The concentrated cone cell area of the retina, directly linked to the ganglion is called the ganglion cells’ receptive field centre

62
Q

What is the significance of the receptive field centre?

A

The bigger the receptive field centre = the less fine detail seen because input from each cone cell is being converged in summation on the ganglion cell

63
Q

Where is the central retina located?

A

Central retina is within the optic nerve head, centred around the fovea centralis

64
Q

What is the foveal pit?

A

In the centre is foveal pit - a region where the photoreceptors are uncovered, no retina between receptors and light path ⇒ no image blur

Image blurs as passes through retinal tissue; scattered

65
Q

Why is the sampling array better in the foveal pit compared to the peripheral retina?

A

Excellent sampling array, as no rod cells present and very thin cone cells packed closely together to maximise space

66
Q

What type of cone cells are present in the foveal pit?

A

Only red and green cells in foveal pit (only red and green cells associated with fine detail, blue cone cells aren’t)

67
Q

Why does the foveal pit allow us to see in greater detail than the peripheral retina?

A

Ganglion cells don’t receive converged input from these cone cells, only receive input from a single cell

68
Q

Summarise the role of peripheral vision

A

Majority of the retina serves only coarse vision:-
- The visual image is optically blurred.
- The cone photoreceptors are large and widely spaced
(separated by larger number of rods).
- The signals from many cones converge onto single
ganglion cells.

69
Q

Outline the functions of central vision

A

The fovea is specialised for high resolution:-
- Good focus – overlying layers are absent
- Only cone photoreceptors, primarily red and green
which are narrow and closely packed
- The signals from the photoreceptors are kept separate
throughout the primary visual pathway

70
Q

What makes the centre of the retina so good at focusing on fine detail?

A

Centre of retina has more associated ganglion than peripheral

71
Q

What is the role of photoreceptors?

A

Photoreceptors report changes in illumination from one moment to another

72
Q

Explain how photoreceptors adapt, every time the eyes rest for a moment or two in the same location

A

Brightness of light strikes a particular photoreceptor→ a strong response produced (ie. depolarisation)

If the eyes stay in the same location, brightness doesn’t change so photoreceptor adapts and resets to RMP → becomes new normal

Due to adaptation, photoreceptors can respond very sensitively to small changes without saturating themselves

73
Q

How do photoreceptors elicit responses in different locations using change sin brightness from one area?

A

Retinal circuitry pulls out changes in brightness from one place to another via lateral inhibition

74
Q

Which ganglion are responsible for lateral inhibition?

A

Ganglion cell receives input from a single cone cell; which is its receptive field centre

Other ganglion receives signals from inhibitory neurons which input info from the whole pool of cones surrounding the central cone ⇒ inhibitory

75
Q

Explain how lateral inhbition works

A

E.g.
Decreased light → depolarisation of cone→ depolarisation of bipolar cell → depolarises ganglion cell

If light decreases on the blue cones → causes depolarisation on the cone, depolarising the inhibitory neurons which go on to inhibit the bipolar cell neuron and ganglion cell

Whatever response is activated across the whole receptor field, is carried out - largely cancels out to produce no response

76
Q

What causes the excitation of retinal ganglion cells?

A

Retinal ganglion cells centres may be excited by either decreases or increases in brightness
Half of all retinal cells respond to increases in brightness

77
Q

What are the 2 excitatory types of retinal ganglion cell?

A
  • on centre ganglions

- off centre ganglions

78
Q

Describe the excitation of off centre ganglion cells

A

The central photoreceptor depolarised by decreased illumination

Bipolar and ganglion cells depolarised by excitatory synapses

79
Q

How are on centre ganglions affected by excitation?

A

The central photoreceptor hyperpolarised (blue) by increased illumination

Bipolar cell depolarized by inverting synapse, excites ganglion cell

80
Q

What are the 2 classes of retinal ganglion cells?

A

Retinal ganglion cells can be divided into different classes

  • Magnocellular
  • Parvocellular
81
Q

Outline the parvocellular class of retinal ganglion cells

A
  • small cell with strong surround
  • sustained responses
  • fine detail vision, but only when image is stable
  • half “on” and half “off” centre
82
Q

Describe the magnocellular retinal ganglion cells

A
  • large cell with weak surround
  • transient responses
  • coarse detail vison, but responds well to fast movement
  • half “on” and half “off” centre
83
Q

How are we able to differentiate colour?

A

Some retinal ganglion cells are wavelength selective

  • parvocellular
  • bistratified
84
Q

Outline the selected wavelengths of parvocellular ganglion cells

A

selective inputs from “red” or “green” photoreceptors
by comparing these responses they can encode wavelength
RED vs GREEN

85
Q

What wavelengths are selected for in bistratified retinal ganglion cells?

A

selective inputs from “blue” or “red+green” photoreceptors
by comparing these responses they can encode wavelength
BLUE vs YELLOW

86
Q

What is the visual role of higher cortical centres of the brain?

A

Higher visual cortical areas have different roles and send signals to different parts of the brain

87
Q

What effect may lesions in the cortical area of the brain have?

A

Lesions in the cortical area processing colour cause colour blindness

88
Q

How are different brain regions innervated to see different detail?

A

Inferotemporal areas get input mainly from parvocellular ganglion to identify detail

Parietal visual areas have a great deal of magnocellular ganglion to see broad shapes

Neurology (20 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions