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Biology 404 > Visual System > Flashcards

Visual System Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

Immature sensory systems develop from a thickening of this germ layer

A

Ectoderm

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2
Q

Immature sensory regions in a developing organism are referred to as…

A

Placodes

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3
Q

Which sensory organ does not develop from a placode? What does it develop from?

A

Retina
Develops from the immature CNS tissue

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4
Q

Define intrinsic signaling

A

Non-receptor-mediated signaling in which signaling factors act on targets in the same cell as they were produced in

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5
Q

Define extrinsic signaling

A

Usually receptor-mediated signaling where signals act on cells other than the cell in which the factor was produced

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6
Q

If all cells have the same DNA, how do they develop differently?

A

Cells express different combinations of TFs which are often concentration gradient-specific

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7
Q

The epidermis, CNS, and Neural crest are all derived from this germ layer

A

Ectoderm

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8
Q

Formation of the 3 germ layers can be observed in this developmental stage

A

Late blastula

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9
Q

The first evidence of neural tissue appears at this developmental landmark

A

Neural induction

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10
Q

BMP is an (intrinsic/extrinsic) signaling factor

A

Extrinsic

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11
Q

When BMP reacts with its receptor, it induces the formation of this kind of tissue

A

Epidermis

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12
Q

When BMP binds to NIFs (e.g. noggin), it induces the formation of this kind of tissue

A

Neural tissue

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13
Q

NIFs are secreted from cells in this germ layer

A

The mesoderm

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14
Q

Noggin, chordin, and follistatin are all examples of

A

NIFs

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15
Q

BMP is part of this family of signaling molecules

A

TGF-Beta

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16
Q

In order for the retina to develop, the CNS has to make direct interactions with (1) during this stage of development (2)

A
  1. The lens placode
  2. The neurula stage
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17
Q

The main role of the cornea is…

A

Protect the eye

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18
Q

The main role of the lens is to…

A

Focus light onto the retina

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19
Q

The main role of the iris is…

A

To regulate the amount of light reaching the retina

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20
Q

Describe the retina

A

A neural tissue present in the eye where light information is detected

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21
Q

The retina sends information to the CNS via…

A

The optic nerve

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22
Q

Why are the cells of the retinal pigmented epithelium pigmented?

A

Melanin helps absorb light - protects cells of the eye from excess oxidation

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23
Q

What is the order of the tissues in the retina starting where the photoreceptor discs are? (6)

A
  • Outer segment
  • Outer nuclear layer
  • Outer plexiform layer
  • Inner nuclear layer
  • Inner plexiform layer
  • Ganglion cell layer
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24
Q

Starting at photoreceptors, what are the cell layers of the retina?

A
  • Photoreceptors
  • Horizontal cells
  • Interneurons (bipolar cells, etc.)
  • Ganglion cells
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25
Q

What are the 2 kinds of photoreceptors and what properties of light do they detect?

A

Rods = Brightness
Cones = Colour

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26
Q

What are the three reasons the retina is an easy area of the CNS to study?

A
  1. Accessible - Isolation of the retina preserves most of its function
  2. Can be grown in explant culture - valid culture system to perform experiments on
  3. It is a “mini-brain” - A lot of the same neurotransmitters and receptors present in neurons are present in the retina
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27
Q

The retina is an extension of this brain region during development (“-cephalon”

A

Diencephalon

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28
Q

Define multipotent cells

A

Cells which are able to give rise to multiple different cell types

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29
Q

(Intrinsic/extrinsic) signaling leads to the development and differentiation of different sensory placodes

A

Extrinsic

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30
Q

Is a juvenile brain technically a sensory placode?

A

No

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31
Q

During later stage neural induction (neural tube stage), the interactions of the lens placode with the CNS start to bend tissues to create this structure

A

The optic vesicle

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32
Q

Which of these sensory structures is more deep (as opposed to cutaneous), the lens placode or the immature CNS?

A

CNS deeper than lens placode

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33
Q

The eye will not be properly formed in the absence of this signaling molecule

A

FGF

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34
Q

BMP and FGF are examples of…

A

Extrinsic signaling factors

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35
Q

Cell autonomous events typically involve signaling by these kinds of molecules

A

Regulatory transcription factors which are tissue/cell specific - intrinsic factors

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36
Q

Cell non-autonomous events typically involve signalling by these kinds of molecules

A

Extracellular signaling factors

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37
Q

What causes the change from multipotent retinal progenitor cells to different mature retinal cell types?

A

Intrinsic transcription factor signaling

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38
Q

What happens first during retinal development, intrinsic or extrinsic cell signaling?

A

Extrinsic first, intrinsic next

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39
Q

True or false: retinal cell types tend to arise at more or less the same time

A

False: different cell types have different “birth” days

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40
Q

What are the general cell types of the retina? (7)

A
  1. Rods
  2. Cones
  3. Muller
  4. Horizontal
  5. Bipolar
  6. Amacrine
  7. Ganglion
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41
Q

Which retinal cell types are born “early”

A

Cones, horizontal, amacrine, ganglion

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42
Q

Which retinal cell types are born “late”

A

Rods, muller, bipolar

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43
Q

How do BMP and FGF contribute to development of the retina?

A

BMP inhibition promotes development of nervous tissue (retina derived from CNS), FGF responsible for development into eyeball

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44
Q

Macular degeneration and retinitis pigmentosa are diseases of the retina which cause…

A

Death of photoreceptors

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45
Q

What kind of cells die in Glaucoma?

A

Retinal ganglion cells

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46
Q

Once photoreceptors are lost, can they be regenerated?

A

No, discs can regenerate but complete cells cannot

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47
Q

What does it mean to have a loss of visual acuity?

A

Loss of central vision, peripheral vision may be fine

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48
Q

What structures are in the outer segment of the retina?

A

Discs of rods and cones

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49
Q

What structures are in the outer nuclear layer of the retina?

A

Rod and cone cell bodies, dendrites of Muller cells

50
Q

What structures are in the outer plexiform layer of the retina?

A

Dendrites/axons of bipolar cells and horizontal cells

51
Q

What structures are in the inner nuclear layer of the retina?

A

Bipolar, Horizontal, Muller, and amacrine cell bodies

52
Q

In what layer of the retina are the ganglion cell bodies?

A

The ganglion cell layer

53
Q

An unproven theory exists where this kind of fiber of the retina may be transporting light to the outer segment

A

Muller cells/muller glia

54
Q

The graded potential between the photoreceptors and the bipolar cells happens in this layer of the retina

A

In the outer plexiform layer

55
Q

How many opsins do rods and cones have respectively?

A

Rods: 1 opsin = rhodopsin
Cones: 3 opsins, s-opsin, m-opsin, l-opsin (sml = short medium long, refers to wavelength)

56
Q

If retinas are dominated by rods, what gives us the ability to see so well during the day?

A

The fovea: focusses light onto the retina

57
Q

What kind of cell is densely packed into the fovea?

A

Cones

58
Q

What retinal layers are missing from the fovea?

A

Inner nuclear layer or ganglion cell layer (no gc bodies, still has connections)

59
Q

What is the difference between the macula and the fovea?

A

The macula makes up a larger area of the retina, the fovea is contained within this area

60
Q

Why is macular degeneration so bad for vision?

A

Because most of the light is focussed onto the macula, particularly on the fovea. Degeneration of this area has a severe effect on vision

61
Q

Central vision is mediated by (1), peripheral vision is mediated by (2)

A
  1. Fovea
  2. Rod-dominated eye (retina outside of the fovea)
62
Q

Describe the brain structures information passes through from the retina to the primary visual cortex

A

Retina > Optic chiasm > Lateral geniculate nucleus > Primary visual cortex

63
Q

Where is the site of phototransduction?

A

PR discs

64
Q

When discs become old, they are shed and engulfed by…

A

Cells of the RPE

65
Q

Where are opsins located in photoreceptors?

A

In the discs

66
Q

Approximately how many stacked discs are there in a photoreceptor?

A

1000

67
Q

What is the main light detector molecule in the mammal eye?

A

Rhodopsin

68
Q

Describe the morphology of rhodopsin?

A

7TM protein, associates with 11cisretinal

69
Q

Where is the retinal attachment site on rhodopsin (which TM region?)

A

TM region 7

70
Q

What associates with the retinal attachment site of rhodopsin?

A

11-cis-retinal

71
Q

11-cis-retinal is converted to all-trans-retinal by…

A

Light

72
Q

Loss of this protein is a key factor in why retinitis pigmentosa patients cannot really see. Why is this?

A

Peripherin-2

Cannot support actin polymerization, so formation of the discs becomes impossible

73
Q

Are photoreceptor discs formed gradually by transport of material via vesicles or are they formed all at once?

A

All at once

74
Q

What happens to photoreceptor discs when the Arp2/3 complex is knocked out?

A

Because Arp2/3 promotes branching, there is no branching, get one big long curled disc instead of little stacked ones

75
Q

In the dark, photoreceptors are (depolarized/hyperpolarized)

A

Depolarized

76
Q

In the light, photoreceptors are (depolarized/hyperpolarized)

A

Hyperpolarized

77
Q

When photoreceptors are depolarized, they release…

A

Glutamate

78
Q

When photoreceptors are hyperpolarized, they release…

A

Nothing!

79
Q

True or false: photoreceptors are more active in the dark

A

True

80
Q

How many bipolar cell types make connections with rods?

A

1

81
Q

How many bipolar cell types make connections with cones?

A

9

82
Q

Bipolar cells can be divided into two categories, which are…

A

On and off

83
Q

What special kind of synapse happens between photoreceptors and underlying bipolar cells/interneurons?

A

Ribbon synapse

84
Q

When someone refers to the “inner retina”, they are referring to these cell types

A

Bipolar and ganglion cells

85
Q

The mammalian eye is particularly attuned to these spatial qualities (2)

A

Directions (directional selectivity)
Contrast (edges, etc.)

86
Q

An “off” bipolar cell will synapse to a (1) ganglion cell

A

Off

87
Q

Why do on and off center bipolar cells respond differently?

A

They have different kinds of glutamate receptors
On: mGluR
Off: iGluR

88
Q

On bipolar cells (depolarize/hyperpolarize) in response to glutamate

A

Hyperpolarize

89
Q

Off bipolar cells (depolarize/hyperpolarize) in response to glutamate

A

Depolarize

90
Q

Ionotropic glutamate receptors when activated cause (depol/hyperpol) of the cell

A

Depolarization (cation channels open)

91
Q

Metabotropic glutamate receptors when activated cause (depol/hyperpol) of the cell

A

Hyperpolarization (cation channels [TRPM1] close)

92
Q

Why do the photoreceptors use graded potentials instead of action potentials to convey information?

A

Info only has to travel a short distance, allows more nuance to be transferred from cell to cell

93
Q

Why do ganglion cells use action potentials instead of graded potentials?

A

Info has to travel all the way to the primary visual cortex - would degrade if using GPs

94
Q

Describe what kind of protein a mGluR is

A

7-TM g-protein coupled receptor (not a channel!)

95
Q

When mGluRs bind to glutamate, TRMP1 channels are (open/closed)

A

Closed = cell hyperpolarized

96
Q

When mGluRs is not bound to glutamate, TRMP1 channels are (open/closed)

A

Open (cell depolarized)

97
Q

When a photoreceptor is hyperpolarized causing an on bipolar cell to be depolarized, this is called a (1)-synapse

A

Sign-inverting synapse

98
Q

Describe the kind of protein that TRPM1 is

A

6TM region cation channel

99
Q

What does TRP of TRPM1 stand for?

A

Transient receptor potential

100
Q

Why do we have the on/off bipolar cell systems?

A

Maximizes the efficiency and speed of visual perception. Specifically, detection of edges and contrast can be maximized by organizing visual fields

101
Q

Describe a simple receptive field

A

When multiple photoreceptors are arranged in a center-surround manner to input to a single ganglion cell

102
Q

What kinds of ions does GABA allow into the cell?

A

Primarily anions, specifically Cl-

103
Q

What neurotransmitter do horizontal cells primarily release?

A

GABA

104
Q

What are the 3 forms of retinoid in the visual cycle?

A

Aldehyde
Alcohol
Ester

105
Q

What is another name for all-trans-retinol?

A

Vitamin A

106
Q

The little units that make up the compound drosophila eye are called…

A

Ommatidia

107
Q

Each ommatidia has 8 photoreceptive cells which are known as…

A

Rhabdomeres

108
Q

R1-R6 (rhabdomeres) are analogous to human…

A

Rods

109
Q

R7 and R8 (rhabdomeres) are analogous to human…

A

Cones

110
Q

Each ommatidia is made of… (3)

A
  1. Lens
  2. Pigment cells
  3. R1-R8 rhabdomeres (one of each)
111
Q

Where are opsins in the fly eye?

A

On the apical surface of the rhabdomeric cells in microvilli (similar to human discs)

112
Q

Photoreceptors in drosophila are described as (1), and in mammals they are described as (2)

A
  1. Rhabdomeric
  2. Ciliary (because the discs extend from a modified cilium)
113
Q

What is the role of the phosphodiesterase in the mammalian phototransduction cascade?

A

Cause the conversion of cGMP to GMP

114
Q

When phosphodiesterase is active, what happens to cGMP levels?

A

Decrease

115
Q

When cGMP is low, what happens to CNG channels? As a result, the cell is (depolarized/hyperpolarized)

A

Not able to open = Cell hyperpolarized

116
Q

What is Ca2+’s role in the phototransduction cascade?

A

Comes in through CNG channels, acts as a second messenger which activates guanylyl cyclase. Guanylyl cyclase converts GTP to cGMP to open CNG channels

117
Q

Describe the direction of light relative to the direction of light perception in mammals versus insects

A

Mammals: light travels opposite processing
Insects: light and processing travel the same direction

118
Q

Which has more extensive visual processing, mammals or drosophila?

A

Mammals

119
Q

How can on and off bipolar cells be distinguished from one another?

A

Have slightly different morphologies and terminate in different layers of the retina

120
Q

Which tends to terminate deeper, on or off bipolar cells?

A

On

121
Q

What is the role of the lateral geniculate nucleus?

A

Relay information from the retina to the cortex

122
Q

In the absence of photoreceptors, the pupillary light reflex will be mediated by these cells

A

Intrinsically photosensitive retinal ganglion cells

Biology 404 (14 decks)

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