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II. Neurophysiology and Perception > Phototransduction and Spectral Sensitivity (M1) > Flashcards

Phototransduction and Spectral Sensitivity (M1) Flashcards

1
Q

What is the net movement of charges (ions) called?

A

current (I)

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2
Q

What is the difference in electrical charge across space called?

A

voltage (V)

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3
Q

Relative to outside of the membrane, is the inside of a neuron more negative or positive? 1. What is the voltage difference numerically? 2

A
  1. negative

2. -60 to -70 mV

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4
Q

A Na+/K+ ATPase pump moves what into the cell (and how much)? 1. What does it move out of the cell (and how much)? 2

A
  1. K+ (2)

2. Na+ (3)

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5
Q

What are the equations that govern the resting ionic gradient across a membrane?

A
  1. Nernst

2. Goldman-Hodgkin-Katz

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6
Q

What did Tomita’s intracellular recordings of membrane action potentials of photoreceptors reveal?

A

resting mem potential of PRs in the dark was less negative (depolarized) than that of a regular neuron (-40 mV)

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7
Q

Do cones depolarize or hyperpolarize in the response to light?

A

hyperpolarize

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8
Q

What type of potentials are light responses (and what does this indicate), making them different than most CNS neuron potentials?

A

graded (the more intense the light stimulus, the greater the hyperpolarization)

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9
Q

What is the numerical resting potential of photoreceptors? 1. What is the maximum light response numerically? 2

A
  1. -40 mV

2. -65 mV

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10
Q

What is the steady flow of ions in darkness in photoreceptors called?

A

the “dark current”

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11
Q

What is responsible for the light evoked hyperpolarization of photoreceptors?

A

Na-permeable channels in the outer segment closing

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12
Q

What is the rods visual pigment called?

A

rhodopsin

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13
Q

What is the cone visual pigment called?

A

opsins or photopsins

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14
Q

What does the visual pigment consist of?

A
  1. opsin protein (7-transmembrane domain receptor)

2. chromophore retinal

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15
Q

What is the retinal formation before absorbing a photon? 1. What is it afterwards? 2

A
  1. 11-cis-retinal

2. all-trans-retinal

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16
Q

What is the name for activated rhodopsin?

A

metarhodopsin II (R*)

17
Q

What is the G-protein involved in phototransduction called? 1. Where is this protein located? 2

A
  1. transducin (Gt)

2. embedded in disk membrane

18
Q

What is the molecule that keeps ion channels open in the photoreceptor?

A

intracellular cGMP

19
Q

What ion movement in the photoreceptor continues while bright light is absorbed (where is it located)?

A

K+ efflux (in inner segment)

20
Q

What aspect of the visual pigment is the same for rods and cones? 1. What is different? 2

A
  1. chromophore (11-cis retinal)

2. opsin protein

21
Q

What is the type of opsin in rods called? 1. Cones? 2

A
  1. rhodopsin

2. S-cone opsin, M-cone opsin, and L-cone opsin

22
Q

Where is opsin produced? 1. What is their lifetime and are they reused? 2

A
  1. inner segment

2. 10-14 days and they are reused

23
Q

What phagocytizes disks that are at the end of the outer segment?

A

RPE

24
Q

What chromosome is the gene for the S opsin found? 1. M opsin? 2. L opsin? 3. Rhodopsin? 4

A
  1. chromosome 7
  2. X chromosome
  3. X chromosome
  4. chromosome 3
25
Q

What is the percent homology between S-opsin and rhodopsin?

A

40%

26
Q

What is the percent homology between S-opsin and M-opsin?

A

45%

27
Q

What is the percent homology between M-opsin and L-opsin?

A

98%

28
Q

When is it thought that human trichromacy arose?

A

after New World and Old World primate split (about 60 million years ago)

29
Q

How many cone pigments do most mammals have?

A

two, dichromacy (S and LM gene)

30
Q

What does the differences in the amino acid sequences in the 4 different types of opsins affect?

A

the relative absorbance

31
Q

What is the wavelength in which the absorption of rhodopsin is greatest/the spectral sensitivity is maximized?

A

500 nm

32
Q

What is the wavelength in which the absorption of S-opsin is greatest/the spectral sensitivity is maximized?

A

425 nm

33
Q

What is the wavelength in which the absorption of M-opsin is greatest/the spectral sensitivity is maximized?

A

530 nm

34
Q

What is the wavelength in which the absorption of L-opsin is greatest/the spectral sensitivity is maximized?

A

560 nm

35
Q

How does an increase in wavelength alter the phototransduction cascade?

A

it doesn’t (all wavelengths go through same phototransduction cascade)

36
Q

What is the idea that once a light photon is absorbed, all info about its wavelength is lost called?

A

Principle of Univariance

II. Neurophysiology and Perception (24 decks)

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