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Ocular Phys Block 11 > Photoreception And Phototransduction > Flashcards

Photoreception And Phototransduction Flashcards

1
Q

Light detection that leads to vision and depends on photoreceptors

A

Photo reception

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2
Q

Photon absorption by visual pigment that is lying on one of the discs in the outer segment of the photoreceptors

A

Photo receptions

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3
Q

Specialized light sensitive neurons

A

Photoreceptors

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4
Q

What is the visible sepctrum of light

A

400-700

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5
Q

Peripheral visual system

A

AKA scotopic

-dim light and motion

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6
Q

Central visual system

A

Photopic

-color and detail

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7
Q

Rods (scotopic_

A

Dim light
Not good for detailed vision
Not good for color
Lower sensitivity to rapidly changing stimuli

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8
Q

Specialized for detailed vision, color vision, less sensitive, and higher sensitive to rapidly changing stimuli

A

Cones (photopic)

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9
Q

Are cones of rods more sensitive

A

Rods

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10
Q

Are cones nad rods more sensitive to rapidly changing stimuli

A

Cones

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11
Q

What photoreceptors are in the fovea

A

Cones

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12
Q

Comprise 97% of photoreceptors

A

Rods

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13
Q

Peak absorption of rods

A

500-510

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14
Q

Rod convergence and sensitivity

A

Increases sensitivity

-may rods gather light information onto one retinal bipolar cell

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15
Q

3% of photoreceptors

A

Cones

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16
Q

More of these in fovea than periphery

A

Cones

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17
Q

L-cone

A

Red cone
560nm
Long wavelength

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18
Q

M-cone

A

Green cone
530nm
Medium wavelength

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19
Q

S-cone

A

Blue cone
420nm
Shirt wavelength

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20
Q

What cones is not present in fovea

A

S cone

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21
Q

Convergence with cones and sensitivity

A

There is no convergence

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22
Q

S cones and rods

A

Very similar to shape as rods, not present in the fovea

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23
Q

Unstable pigmented that undergo a chemical change when they absorb light

A

Photopigments

24
Q

Protein (opsin) + Chomophore

A

Photopigmentes

25
Q

Opsin + 11=cis retinal (chromophore)

A

Rhodopsin

26
Q

Used for vision in dim light

A

Rhodopsin

27
Q

More stable and abundant than con pigments. Insoluble in water

A

Rhodopsin

28
Q

What are the three different cones

A

Different iodopsins
Red
Blue
Yellow

29
Q

The series of biochemical events that lead from photon capture by a photoreceptors cell to its hyperpolarixation and slowing of NT release at the synapses

A

Phototransudction

30
Q

Transformation of light into electrical and chemical signals that produces the perception of light

A

Phototransduction

31
Q

First messengers

A

Can be growth hormones, NT, light

  • cant pass into the cell, can only work on the receptors on the membrane
  • transforms signal into molecules inside the cells to pass the signal
32
Q

2nd messengers

A

Molecules in the cells that respond to the receptor binding a 1st messenger that causes a response

33
Q

1st messenger in light transduction

A

Light

34
Q

Cellular response to light binding

A

Closure of CNG channel

35
Q

Cyclic-GMP-Gated-Cation Channel (GNC)

A
  • allow Na+ and K+ and Ca2+ to enter the cell

- causes the cells to be partially depolarized (-50mV)

36
Q

Resting membrane potnetion in the dark

A

Rods: -50mV

Other neurons: -70mV

37
Q

There is a net flux of cation outer and inner segment plasma membrane and a net flux of cations into the outer segment plasma membrane, as well as electrical conductance between the inner and outer segment, a complete circuit is made

A

Dark current

38
Q

Biochemical cascade of light transduction

A

I. Photoisomeraiztion of rhodopsin
IIG protein activation
III. PDE6 activation
IV. Channel closing

39
Q

Photoisomeraixation of rhodopsin

A

Opsin (11-cis-retinal)-rhodopsin (light-MII

  • reduction of all-trans-retinal into all-trans-retinol occurs in photoreceptors
  • reisomerization of all-trans-retinol into 11-ci-retinal, occurs in RPE
40
Q

G protein activation

A
  • metarhodopsin II encounters an inactive G protein
  • the Ga subunit of the G protein comes to lie over the MII
  • GDP is replaced by GTP (G protein binds to GTP-on, G Protein binds to GDP-off)
  • GTP binds to Ga, the protein is active
  • Ga-GTP unit separates from both MII and the By portion of the G protein
41
Q

G protein binds to GTP

A

On

42
Q

G protein binds to the GDP

A

Off

43
Q

PDE6 activation

A

The activated G protein binds with a molecule named cGMP phosphodiesteraee PDE6
-activated PDE6 converts the cGMP into CMP, PDE can degrade cGMP by hydro;lazing cGMP into gā€™-GMP)

44
Q

Channel closing

A
  • reduction of cGMP concentration causes CNG channel closure
  • opening of CNG channel put photoreceptors at resting dark adapting state
45
Q

Phototransuction

A

Phototransuction
Biochemical cascade
Electronic spread
Slowing of NT release

46
Q

What does closing the channel do

A

Reduces the Na and Ca ions into the cell, reducing the dark current and making the membrane potential more negative

  • photocurrent in dark: cations moving into the cell
  • photocurrnt in light: a single photo isomerization closes ion channels and causes a 2% reduction in the photocurrent
47
Q

Communication of rods with downstream bipolar cells by the release of

A

Glutamate

48
Q

High level glutamate released by rods

A

Signal total darkness to bipolar cells

49
Q

Adaptation

A

Alters sensitivity to light, decreases sensitivity in response to bright light, increases sensitivity in responsive to dim light, controlled by Ca influx

50
Q

Which photoreceptors sensitivity increases due to convergence

A

Rods

51
Q

Rhodopsin in rods is composed of

A

Opsin + 11-cis-retinal

52
Q

Which one is the right pair?

A

L-cone and red/yellow light

53
Q

Which one is the beginning step of biochemical cascade of phototransuction

A

Photoisomerixation of rhodopsin

54
Q

Which one is a key molecule of biochemical cascade to keep CNG channel open

A

CGMP

55
Q

Which one is a NT between rods and bipolar cells

A

Glutamate

Ocular Phys Block 11 (6 decks)

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