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NSCI 201 > Visual system > Flashcards

Visual system Flashcards

1
Q

Place the following anatomical parts of the eye in the right order: retina, retinal pigment epithelium, cornea, lens, pupil.

A

Cornea > pupil > lens >retina > retinal pigment epithelium.

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2
Q

Where does the retina get thinner?

A

In the fovea.

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3
Q

What are the mechanisms of the eye to adjust vision?

A
  • Pupil size (modulating how much light enters the eye)

- Lens’ thickness (modulated by the ciliary muscles to adjust the refractive intensity of the eye)

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4
Q

What vision problem occurs from the lens losing too much elasticity (i.e. accommodation power decreasing, often with age)?

A

Presbyopia.

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5
Q

What is color blindness caused by?

A

Missing a cone type.

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6
Q

What vision problem arises from spherical aberrations of the eye (creating multiple focal points)?

A

Astigmatism

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7
Q

What is the difference between macula and fovea?

A

Macula is the part of the retina that is responsible for high resolution vision. Fovea is the central part of macula, responsible for the highest resolution vision.

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8
Q

What are the 5 main neuronal cell types found in the eye?

A
  • Photoreceptors (rods AND cones)
  • Bipolar cells
  • Ganglion cells
  • Horizontal cells
  • Amacrine cells
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9
Q

True of false: rods vastly outnumber cones.

A

True.

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10
Q

Give three reasons for which visual acuity is increased in the fovea.

A
  1. Skinnier cones allow them to be densely packed.
  2. Rest of retinal cells are pushed to the side (makes some space for light to hit directly the cones).
  3. Avascular (no blood vessels), so light directly hits the cones of the fovea and there’s more room to stack them.
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11
Q

Who (what cell), in the first place, generates the visual signal?

A

Photoreceptors.

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12
Q

Photoreceptors fire graded potentials, not APs, and it is thought to still be efficient. Why?

A

Electrical impulses only have a very short distance to travel (against impulses travelling along long axons of PNS).

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13
Q

What is counter-intuitive about the excitation of photoreceptors?

A

Photoreceptors stop (or drastically slow the rate of) releasing Glu in presence of light because they become hyperpolarized.

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14
Q

Describe the movement of Na+, Ca++ and K+ when levels of cGMP are high and low in the membrane of a photoreceptor.

A

In the dark, levels of cGMP are high, opening the cGMP-gated channel for the inward flow of Na+ and Ca+: Na+ and Ca2+ are flowing IN, K+ is flowing OUT = membrane slightly depolarized

In the presence of light, cGMP levels are low, closing the cGMP-gated channel for the inward flow of Na+ and Ca+: Na+ and Ca2+ are NOT flowing IN, K+ is flowing OUT = membrane hyperpolarized

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15
Q

Describe the phototransduction cascade in rods (from light hitting the photoreceptor to hyperpolarization).

A

Light hitting retinal molecules in membrane-attached opsin proteins -> retinal molecules go through a conformational change (11-cis to all-trans conf.) -> activation of rhodopsin channels -> transducin activated (G prot.) -> PDE (phosphodiesterase) activated -> cGMP hydrolyzation ->low [cGMP] -> closure of cGMP-gated channels ->Na+ and Ca++ no more flowing in -> photoreceptor membrane hyperpolarized.

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16
Q

Provide the 5 steps of the retinoid cycle.

A
  1. All-trans retinal dissociates from opsin and diffuses in cytosol
  2. All-trans retinal converted to all-trans retinol
  3. All-trans retinol shuttled to retinal pigment epithelium via IRBP
  4. All-trans retinol converted to 11-cis retinal
  5. 11-cis retinal shuttled back to opsin by IRBP
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17
Q

What are the 3 cone types?

A

Short wavelength -> blue light
Medium wavelength ->green light
Long wavelength ->red light

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18
Q

From what does colour arise?

A

Comparing contrasting responses of different cone types.

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19
Q

Name 4 differences between OFF and ON bipolar cells of the cones.

A

OFF:

  • Ionotropic
  • Depolarized when photoreceptors fire in the dark
  • Connect to OFF ganglion cells
  • Stratify in upper layers of IPL (above 2-3)

ON:

  • Metabotropic
  • Depolarized when photoreceptors fire in the light
  • Connect to ON ganglion cells
  • Stratify in deeper layers of IPL (under 3)
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20
Q

Bipolar cells fire APs or graded potentials?

A

Graded potentials.

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21
Q

True or false: what happens in the photoreceptors inversly happens in the ON bipolar cells (in terms of graded potentials).

A

True

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22
Q

In proportion to photoreceptors, the distribution of bipolar cells is specially low in one emplacement of the retina. What emplacement is that?

A

The fovea.

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23
Q

How is the intensity of light conveyed in electrical signal?

A

By the graded signals frequency.

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24
Q

True or false: rods only have ON bipolar cells.

A

True.

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25
Q

True or false: rods have a direct pathway to ganglion cells.

A

False: rod signals hijack the cone bipolar system to reach its ganglion cells.

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26
Q

OFF-center ganglion cells are ____ by light in their ____ receptive field and ____ by light in their ____ receptive field, whereas ON-center ganglion cells are ____ by light in their ____ receptive field and ____ by light in their ____ receptive field.

Place:

excited x2
inhibited x2
surround x2
center x2

A

OFF-center ganglion cells are excited by light in their surround receptive field and inhibited by light in their center receptive field, whereas ON-center ganglion cells are excited by light in their center receptive field and inhibited by light in their surround receptive field.

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27
Q

What cells can provide lateral inhibition to photoreceptors, bipolar cells and ganglion cells?

A

Horizontal cells provide negative feedback to photorecetors.

Amacrine cells can provide lateral inhibition to bipolar cells and ganglion cells.

28
Q

How are center-surround receptive fields determined?

A

By the negative feedback of horizontal cells.

29
Q

Horizontal cells have the biggest receptive field, how does that correlate with their role?

A

They need to possess a large receptive field to impart the center-surround receptive fields to photoreceptors.

30
Q

How do relate luminance, light intensity and brightness?

A

Luminance is the physical property of light intensity and brightness is its perception.

31
Q

By what is imparted the direction selective character of some ganglion cells?

A

By their asymmetrical lateral inhibition caused by the Starburst amacrine cells.

32
Q

What are the three predominant ganglion cells in the human retina?

A

Parasol, midget and bistratified.

33
Q

What is a concrete example of colour opponency in the human eye?

A

Red-on-green-off midget ganglion cells.

34
Q

True or false: majority of the axons of the optic nerve cross over the midline.

A

True (60%).

35
Q

Link the following brain regions to the role they correspond to.

Brain regions:

  • Hypothalamus
  • Superior colliculus
  • Primary visual cortex

Roles:

  • Conscious vision
  • Head and eye movements to visual targets
  • Regulation of circadian rhythm
A

Regulation of circadian rhythm - Hypothalamus
Head and eye movements to visual targets - Superior colliculus
Conscious vision - Primary visual cortex

36
Q

Describe the pupillary light reflex pathway.

A

Some ganglion cells (responding to photorecpetors expressing melanopsin) send their axon to prectectum via optic nerve → projecting axons to EWN (Edinger-Westphal nuclei) in midbrain ipsilaterally and contralaterally → projecting axons via oculomotor nerve to ciliary ganglion cells → ciliary ganglion cells innervate constrictor muscle of iris (BOTH pupils respond to MONOcular visual stimulation)

37
Q

Describe the overall pathway of conscious vision (primary visual pathway).

A

Optic nerve -> LNG -> V1 (primary visual cortex)

38
Q

The optokinetic reflex is composed of two distinct eye movements. What are they? What ganglion cells are essential to this reflex?

A

Saccades and smooth pursuits.

Direction selective ganglion cells.

39
Q

Temporal retina is situated ____ while nasal retina is situated ____. Nasal retina processes principally the ____ visual field while temporal retina processes principally the ____ visual field.

Words to place:

proximally
central
distally
lateral

A

Temporal retina is situated distally while nasal retina is situated proximally. Nasal retina processes principally the lateral visual field while central retina processes principally the central visual field.

40
Q

True or false: images entering the eye are inverted on two axes.

A

True (vertically and horizontally).

41
Q

True or false: monocular vision exists in the human eye.

A

True: in the extremities of the visual field.

42
Q

True or false: inferior retinal quadrants and superior retinal quadrants take the same path from LGN to V1.

A

False: different paths.

43
Q

For every layer of LGN (and interlayer), describes its ganglion cell type, what visual property it is responsible for and where it projects in V1.

A

Ventral layers (1-2):

  • Magnocellular type
  • Motion sensitive
  • Projet to layer 4Cα in V1

Dorsal layers (3-4-5-6):

  • Parvocellular type
  • Color sensitive
  • Project to layer 4Cβ in V1

Between every layer of LGN:

  • Koniocellular type
  • Unclear function
  • Project to patches in layer 2/3 of V1
44
Q

Which layer of the primary visual cortex is the main input layer for vision?

A

Layer 4C.

45
Q

What are the cortical divisions of V1?

A 
Layers...
1
2/3
4A
4B
4Cα
4Cβ
5
6
46
Q

What is the main difference between superficially and deeply located pyramidal cells in V1?

A

Superficially located pyramidal cells project to other cortical areas.
Deeply located pyramidal cells project to subcortical targets (LGN and superior colliculus).

47
Q

What is an an orientation column in V1?

A

Cells immediately above or below one another in different cortex layers taht process the SAME location in the visual field and share similar selective responses.

48
Q

What are orientation pinwheels in V1?

A

In every receptive field composing the visual field, all orientation-selective cells are present, forming a repeating “pinwheel” pattern in V1.

49
Q

What is stereopsis? Where does it anatomically arise?

A

Perception of depth driven by reception of visual information deriving from both eyes in the brain. Arises in V1 (not at the eye level)

50
Q

List 4 levels of organization in the visual system.

A
  • Retinotopic maps
  • Orientation pinwheels
  • Ocular dominance columns
  • Color blobs
51
Q

What are the ventral and dorsal pathways (their steps)? What are the key words we can assign to them?

A

Ventral:
V1 →V2 →V4 →temporal lobe
“What” pathway

Dorsal:
V1 →V2 →MT →parietal lobe
“Where” pathway

52
Q

What are the two types of strabismus?

A

Esotropia and exotropia.

53
Q

What condition can result from untreated strabismus?

A

Amblyopia.

54
Q

What is MT in the dorsal stream known for? What is V4 in the ventral stream known for?

A

MT is known for its sensibility to motion.

V4 is known for its high percentage of color selective cells.

55
Q

What is the aperture problem concerning V1? How is it overcame?

A

The visual receptive field of V1 cells is small, making it likely to provide misleading information about direction of movement (only integrates a part of the movement). The problem is overcame by the integration in MT of the V1 neurons’ inputs.

56
Q

What differentiates cataract, glaucoma, macular degeneration, retinitis pigmentosa, diabetic retinopathy from blindsight, hemispatial neglect, cerebral akinetopsia and prosopagnosia?

A

The first conditions are attributable to eye problems, while the others are attributable to higher order processing deficiencies (in the brain).

57
Q

What is the first leading cause of blindness?

A

Cataract

58
Q

What is the cause of glaucoma?

A

Diseases damaging optic nerve (slow onset).

59
Q

What is macular degeneration affecting?

A

Photoreceptors in macula and and fovea. In the case of wet AMD, leaky blood vessels (in macula) disturb connection between retina and retinal pigment epithelium, obstructing photoreceptors.

60
Q

What is the cause of retinitis pigmentosa and what are its consequences?

A

Caused by an heterogenous group of hereditary diseases. Causes photoreceptor degeneration in the peripheral retina -> creates tunnel vision and night-blindness.

61
Q

In what does result diabetic retinopathy?

A

Macular oedema (blood vessels leaking their content on retina).

62
Q

What is the cause of blindsight?

A

Damage to primary visual cortex = conscious blindness. Other forms of subconscious vision can still persist.

63
Q

True or false: hemispatial neglect arises from the damage to the left eye.

A

False: most often arises from strokes and brain injury occuring unilaterally in the right cerebral hemisphere in the parietal lobe.

64
Q

What is the link between cerebral akinetopsia and middle temporal area (MT)?

A

Cerebral akinetopsia, known as motion blindness, arises from damage to MT.

65
Q

What does cause the damage or the improper development of face selective visual regions in the inferotemporal cortex?

A

Prosopagnosia.

66
Q

What are 4 known vision restoration techniques?

A

Cell therapy, gene therapy, retinal prosthetic implants and optogenetic therapy.

67
Q

How is transducin inactivated?

A

Arrestin.

NSCI 201 (14 decks)

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