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II. Neurophysiology and Perception > Dark Adaptation (M1) > Flashcards

Dark Adaptation (M1) Flashcards

1
Q

What are the methods for halting phototransduction?

A
  1. R* phosphorylation by rhodopsin kinase
  2. Interaction of R* and transducin blocked by arrestin
  3. Transducin inactivation by GTP hydrolysis, which is sped up by GTPase accelerating proteins like RGS9
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2
Q

What problems do people with defective RGS9 proteins have?

A
  1. take longer to light adapt
  2. hard to follow a ball in the air
  3. slow ERG recovery (no response to 2nd stimulus)
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3
Q

What is term for slow photoresponse recovery?

A

bradyopsia

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4
Q

What is the major benefit of having a phototransduction halting system?

A

enhances temporal resolution (can discriminate different stimuli in short period of time)

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5
Q

What occurs following the absorption of a photon to the chromophore and beyond?

A
  1. the chromophore (11-cis retinal) changes to all-trans retinal
  2. photopigment activated and transparent to light (bleaching)
  3. chromophore converted back to 11-cis retinal
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6
Q

What is the peak wavelength rhodopsin absorbs in dark adapted retinas or retinal homogenate? 1. What color does the retina appear? 2

A
  1. 500nm

2. red/brown (long-wavelength reflected back)

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7
Q

What is the peak wavelength rhodopsin absorbs after exposure to light with the retina looking yellow?

A

380nm

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8
Q

What is the peak wavelength rhodopsin absorbs as all-trans retinal gets converted to vitamin A? 1. What color does the retina appear? 2

A
  1. 320nm

2. white (bleaching)

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9
Q

What is the chromophore used by photoreceptors a derivative of?

A

vitamin A

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10
Q

What is often the initial sign of vitamin A deficiency?

A

night blindness

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11
Q

What is the disease associated with juvenile macular degeneration? 1. What is the inheritance type? 2

A
  1. Stargardt’s disease

2. autosomal recessive

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12
Q

What is the gene that encodes protein in rod/cone disks involved in chromophore removal from opsin? 1. In what disease has this found to be mutated? 2. What is the result? 3

A
  1. ABCR gene
  2. Stargardt’s disease
  3. toxic accumulation of chromophore-bound lipofusin in RPE and subsequent retinal degeneration
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13
Q

What is retinal densitometry used for?

A
  1. assess degree of bleached vs regenerated photopigment

2. map out individual cone types (with scanning laser ophthalmoscope)

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14
Q

What is the average percentage of S-cones of all the cones in the retina?

A

7-10%

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15
Q

What is the average percentage of M-cones of all the cones in the retina?

A

about 30%

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16
Q

What is the average percentage of L-cones of all the cones in the retina?

A

about 60%

17
Q

What is the range of variability in the ratio of M-cones to L-cones?

A

1M:1L to 1M:3L

18
Q

Where is the S-cones peak density? 1. Where are they missing from the retina? 2. Why are they missing here? 3

A
  1. just outside of the central region
  2. small center region of fovea
  3. maximize acuity by reducing chromatic aberrations
19
Q

How long does 50% rhodopsin photopigment regeneration take? 1. Near-complete regeneration? 2

A
  1. 7 minutes

2. 35 minutes

20
Q

How long does 50% opsin (cone) photopigment regeneration take? 1. Near-complete regeneration? 2

A
  1. 2 min

2. 8 min

21
Q

What is the adjustment of the operating level of the visual system to lower light levels?

A

dark adaptation

22
Q

What is the threshold difference between rods and cones on a dark adaptation curve called?

A

photochromatic interval

23
Q

How would the dark adaptation curve be altered if a large 700nm test light was used instead of 420nm?

A

cone only curve would be seen because rods not effected

24
Q

What happens to rod dark adaptation with age? 1. Why does this occur? 2. What disease accelerates the aging process? 3

A
  1. slows
  2. reduced availability of retinal
  3. ARMD and retinitis pigmentosa
25
Q

Where is drusen located in the retina?

A

between choroid and RPE

26
Q

What kind of cells can get regenerated chromphore from a different source besides RPE? 1. What cells provide this? 2

A
  1. cones

2. Muller cells

27
Q

What does a SST-1 screen for?

A

diseases that affect rods (RP, Vit A deficiency, CSNB) and ARMD

28
Q

Does bleaching 50% of a retina increase a threshold (makes worse) by more, less or exactly double?

A

much more

II. Neurophysiology and Perception (24 decks)

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