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neuroscience > Retinal Phototransduction > Flashcards

Retinal Phototransduction Flashcards

1
Q

What structure does the following statement describe?

A spherical and avascular, white dense connective tissue that covers the globe posterior to the cornea.

A

Sclera

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2
Q

Which structure provides a strong tough external framework to protect the delicate optic and neural structures?

A

sclera

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3
Q

What structure does the following statement describe?

A mechanically strong and transparent connective tissue that covers the anterior 1/6 surface of the eye

A

Corea

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4
Q

What is the post powerful focusing element of the eye?

A

The cornea

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5
Q

What structure does the following statement describe?

A specialized epithelial tissue that is responsible for fine-tuning the image that is projected on the retina

A

the lens

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6
Q

Where is the lens of the eye located?

A

Inside the eye, surrounded by aqueous humor

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7
Q

What stabilizes the lens and allows for accommodation?

A

Elastin based zonular fibrils

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8
Q

What do these three structure compose?

Choriod, ciliary body, iris

A

Uveal tract

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9
Q

What structure does the following statement describe?

Capillary bed nourishing the photoreceptors and outer retina.

A

choroid

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10
Q

What structure does the following statement describe?

A structure composed of the ciliary muscle, controlling the refractive power of the lens, and a vascular component, that produces the aqueous humor filling the anterior chamber

A

Ciliary body

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11
Q

What structure does the following statement describe?

Colored portion of the eye, seen through the cornea

A

Iris

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12
Q

What does the Iris contain?

A

It contains 2 sets of muscles with opposing actions that allow the size of the pupil to be adjusted.

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13
Q

What is the anterior chamber?

A

Volume behind the cornea and in front of the lens. It is filled with aqueous humor

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14
Q

What is the posterior chamber?

A

region between the vitreous and the lens

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15
Q

What structure does the following statement describe?

Clear watery liquid that nourishes the cornea and lens and produced by the ciliary body

A

Aqueous humor

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16
Q

What structure does the following statement describe?

Thick gelatinous substance filling the space between the back of the lens and the surface of the retina

A

Vitreous humor

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17
Q

What structure does the following statement describe?

Contains neurons that absorb light and process visual information in the images and send that information to the brain

A

Retina

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18
Q

What is the macula?

A

Oval spot containing a yellow pigment

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19
Q

What is the fovea?

A

Small depression at the center of the macula (has high spacial acuity)

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20
Q

What structure does the following statement describe?

Whitish circular are where retinal axons leave the eye and travel through the optic nerve to targets in the midbrain and thalamus

A

Optic disk

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21
Q

Where do blood vessels supplying the inner retina enter the eye?

A

optic disc

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22
Q

What is the blood supply to the eye?

A

Ophthalmic artery (anterior segment and retinal system)

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23
Q

What are cataracts?

A

Clouding of the lens that affects vision. There is a disruption of the order of the organization of the lens cell fibers or aggregation of the proteins within them can destroy transparency of the cell

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24
Q

What are the symptoms of cataracts?

A

hazy vision, poor night vision, glare and faded colors

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25
Q

What is the treatment for cataracts?

A

surgical removal of the cloudy lens and replacement with an artificial lens

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26
Q

What is glaucoma?

A

A group of diseases that damage the eye’s optic nerve and can result in vision loss (peripheral at first)

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27
Q

Is glaucoma reversible?

A

No, it is not

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28
Q

What are the types of glaucoma?

A

Normal tension, open- angle, closed- tension

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29
Q

What is a major risk factor for glaucoma?

A

Elevated eye pressure, thin cornea, abnormal optic nerve anatomy, high blood pressure

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30
Q

Describe the structure of the retina

A

Organized layers of neurons (3 nuclear layers, 2 plexiform layers, 1 fiber layer)

1) Ganglion layer
2) Inner plexiform layer
3) Inner nuclear layer
4) Outer plexiform layer
5) Outer nuclear layer

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31
Q

What are teh 5 types of neurons in the retina?

A

Photoreceptors, horizontal cells, bipolar cells, amacrine cells, ganglion cells

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32
Q

Where is pigmented epithelium found and what is its function?

A

It is found behind the photoreceptors and acts as a backstop for light and maintains phototransduction machinery of photoreceptors by recycling photoreceptor discs

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33
Q

How does neurotransmission occur in the retina?

A

cells along the vertical path release glutamate

cells mediating lateral information transmission release GABA or glycineric

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34
Q

What is vertical information flow?

A

Photoreceptors —-> bipolar cells —–> ganglion cells

35
Q

What is lateral information flow?

A

Mediated by horizontal cells and amacrine cells

36
Q

What are the two types of photoreceptros in the retina?

A

Rods and cons

37
Q

True or False:

Photoreceptors are ciliated cells

A

True

38
Q

What are the structural components of the photoreceptors?

A

Outer segment (has phototransduction machinery)

Inner segment (has cell organelles)

Synaptic terminal (contacts bipolar and horizontal cells)

Neurotransmitter (glutamate)

39
Q

How do receptors respond to light?

A

with graded hyperpolarizations

40
Q

What is circulating current?

A

Na and Ca in through cGMP gated channels and K in through channels. COmbined action depolarizes the cell to a steady -40

41
Q

What happens to the inward cationic current when the photorecetpors are exposed to light?

A

The Na and Ca channels are closed but the K channel remains open and this hyperpolarizes the cell

42
Q

What does teh phototransduction cascade provide for?

A

High amplification which allows rods to respond to absorption of a single photon

43
Q

What is phototransduction?

A

Process by which light is converted into electrical signals

44
Q

Describe the process of pigment activation?

A

Pigment, which has opsins (G protein linked receptors with 11-cis retinal) are activated by absorbing a photon and changing the conformation of the retinal. This then activates rhodopsin. Activated rhodopsin can then decrease cGMP levels and close Na and Ca channels

45
Q

What is dark adaptation?

A

Restoration of sensitivity after exposure to illumination. It occurs mostly in the pigment epitheloum

46
Q

Does the following statement describe rods or cones?

High sensitivity and low resolution

A

Rods

47
Q

Does the following statement describe rods or cones?

Low sensitivity and high resolution

A

cones

48
Q

True of false:

High convergence of cones onto bipolar cells

A

False. There is a high convergence of RODS into rod bipolar cells. There is 1 cone per 1 bipolar (midget) cells

49
Q

What is the leading cause of vision loss?

A

Age related macular degeneration - dry (85%)

50
Q

Describe wet age related macular degeneration?

A

abnormal bvs behind retina grow under macula

leak and rapidly damage retina

51
Q

Describe dry AMD?

A

retinal pigment epithelium and photoreceptors of macula degenerate
-accumulation of yellow deposit - cell debris

52
Q

What are the symptoms of age related macular degeneneration? What are some associated risk factors?

A

Loss of central vision and acuity (cones)

-aging, smoking, inheritance

53
Q

What type of glutamate receptors are in an on center bipolar cell? in a off center bipolar cell?

A

on center: inhibitory
-in response to light, decreased glutamate released from photoreceptors causes less of an inhibitory response –> depolarization

off center: excitatory
-in response to light, decreased glutamate released from photoreceptors causes less of an excitatory response –> hyperpolarization

54
Q

Describe nonproliferative vs proliferative diabetic retinopathy?

A

nonproliferative: hyperglycema-> pericyte death
- microaneurysms and dot hemorrhages

proliferative - new fragile vessels grrow
-leak blood

55
Q

Describe an on center bipolar cell:

  1. ? in the center -
  2. ? in surroundings
  3. responds to:
A
  1. excitatory in the center - depolarization
  2. inhibitory in surroundings - hyperpolarization
  3. responds to light going on
    - light against dark background
56
Q

Describe an off center bipolar cell:

  1. ? in the center -
  2. ? in surroundings
  3. responds to:
A
  1. inhibitory in center - hyperpolarize
  2. excitatory in surroundings - depolarize
  3. respond to lights going off
    - dark spot against light background
57
Q

Ganglion cell’s firing rate is most affected by what?

A

receptive fields lying along border of illumination

58
Q

In an on center ganglion cell describe the effects:

  1. receptive field in dim light
  2. illumination on inhibitory surround
  3. border of illumintation falls on middle of receptive field
  4. center of receptive field is full illuminated
    - portion is in dark area
A
  1. spontaneous activity
  2. reduced discharge
  3. no change in rate - excitatory and inhibitory cancel out
  4. only partial inhibition - strong discharge
59
Q

What determines the on or off center properties of bipolar cells and the ganglion cells they innervate?

A

glutamate receptors

60
Q

What type of glutamate receptors are in an on center bipolar cell? in a off center bipolar cell?

A

on center: inhibitory

-in response to light, decreased glutamate released from photoreceptor

61
Q

What helps detect the borders of objects?

A

color

62
Q

Do rods have a high or low convergence onto rod bipolar cells?

A

High convergence

63
Q

What is scotopic vision?

A

rod only vision (no color)

64
Q

What is photopic vision?

A

cone only vision (color)

65
Q

What is mesopic vision?

A

rod and cone vision

66
Q

At low light levels, which photoreceptors are active?

A

Rods only

67
Q

What colors are the basis for trichromatic vision, and what enables this to occur?

A

blue, green, red

opsin sequences of the cones on the disk tune the absorption of light to a particular region of the spectrum

68
Q

Which opsin types are similar in sequence, which are different?

A

Rho and S-opsin different
S-opsin and M-opsin different

M and L have few differences

69
Q

In the cone mosaic, which opsin is the least present, and which opsins is there a large ratio of variability present in different people?

How does this ratio affect color perception?

A

S-opsin - only 5%

M and L - large differences in ratio present
-no impact on color perception

70
Q

What occurs in color blindness?

A

there is a change in number of genes coding for red and green cone opsins

71
Q

What type of color blindness does this describe: no expression of M opsin?

A

deuteranopia

72
Q

What is protanopia?

A

color blindness: no expression of L opsin

73
Q

What is tritianopia?

A

color blindness: no expression of S opsin

-very uncommon

74
Q

Where are M cells found and what do they do?

A

in the periphery

they sense motion and are not color sensitive

75
Q

What word describes the pathway of M cells?

A

magnocellular

76
Q

Are M cells large or small, and what does this mean?

A

large cells that receive input from large number of photoreceptors

77
Q

What word describes the pathway P cells are involved in?

A

paravocellular

78
Q

What are P cells involved in?

A

High acuity and color sensitivity

79
Q

Which type of cell P or M has good light and contrast sensitivity and temporal resolution?

A

M cells

80
Q

Where are P cells found? How many cells do they receive input from?

A

fovea

receives input from single bipolar cell which receives input from single cone

81
Q

What type of cell is a K cell and what is it’s function?

A

bistratified ganglion cells

-carry short wavelength - blue info

82
Q

How is color determined in relation to cones?

A

comparisons btwn two or more cone types

83
Q

What type of cells are involved in synchronization of circadian rhythms, sleep, learning?

A

photosensitive retinal ganglion cells

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