Photoreception And Phototransduction

Question 1

Light detection that leads to vision and depends on photoreceptors

Answer 1

Photo reception

Question 2

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

Answer 2

Photo receptions

Question 3

Specialized light sensitive neurons

Answer 3

Photoreceptors

Question 4

What is the visible sepctrum of light

Answer 4

400-700

Question 5

Peripheral visual system

Answer 5

AKA scotopic

-dim light and motion

Question 6

Central visual system

Answer 6

Photopic

-color and detail

Question 7

Rods (scotopic_

Answer 7

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

Question 8

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

Answer 8

Cones (photopic)

Question 9

Are cones of rods more sensitive

Answer 9

Rods

Question 10

Are cones nad rods more sensitive to rapidly changing stimuli

Answer 10

Cones

Question 11

What photoreceptors are in the fovea

Answer 11

Cones

Question 12

Comprise 97% of photoreceptors

Answer 12

Rods

Question 13

Peak absorption of rods

Answer 13

500-510

Question 14

Rod convergence and sensitivity

Answer 14

Increases sensitivity

-may rods gather light information onto one retinal bipolar cell

Question 15

3% of photoreceptors

Answer 15

Cones

Question 16

More of these in fovea than periphery

Answer 16

Cones

Question 17

L-cone

Answer 17

Red cone
560nm
Long wavelength

Question 18

M-cone

Answer 18

Green cone
530nm
Medium wavelength

Question 19

S-cone

Answer 19

Blue cone
420nm
Shirt wavelength

Question 20

What cones is not present in fovea

Answer 20

S cone

Question 21

Convergence with cones and sensitivity

Answer 21

There is no convergence

Question 22

S cones and rods

Answer 22

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

Question 23

Unstable pigmented that undergo a chemical change when they absorb light

Answer 23

Photopigments

Question 24

Protein (opsin) + Chomophore

Answer 24

Photopigmentes

Question 25

Opsin + 11=cis retinal (chromophore)

Answer 25

Rhodopsin

Question 26

Used for vision in dim light

Answer 26

Rhodopsin

Question 27

More stable and abundant than con pigments. Insoluble in water

Answer 27

Rhodopsin

Question 28

What are the three different cones

Answer 28

Different iodopsins Red Blue Yellow

Question 29

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

Answer 29

Phototransudction

Question 30

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

Answer 30

Phototransduction

Question 31

First messengers

Answer 31

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

Question 32

2nd messengers

Answer 32

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

Question 33

1st messenger in light transduction

Answer 33

Light

Question 34

Cellular response to light binding

Answer 34

Closure of CNG channel

Question 35

Cyclic-GMP-Gated-Cation Channel (GNC)

Answer 35

- allow Na+ and K+ and Ca2+ to enter the cell | - causes the cells to be partially depolarized (-50mV)

Question 36

Resting membrane potnetion in the dark

Answer 36

Rods: -50mV | Other neurons: -70mV

Question 37

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

Answer 37

Dark current

Question 38

Biochemical cascade of light transduction

Answer 38

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

Question 39

Photoisomeraixation of rhodopsin

Answer 39

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

Question 40

G protein activation

Answer 40

- 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

Question 41

G protein binds to GTP

Answer 41

On

Question 42

G protein binds to the GDP

Answer 42

Off

Question 43

PDE6 activation

Answer 43

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 g’-GMP)

Question 44

Channel closing

Answer 44

- reduction of cGMP concentration causes CNG channel closure - opening of CNG channel put photoreceptors at resting dark adapting state

Question 45

Phototransuction

Answer 45

Phototransuction Biochemical cascade Electronic spread Slowing of NT release

Question 46

What does closing the channel do

Answer 46

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

Question 47

Communication of rods with downstream bipolar cells by the release of

Answer 47

Glutamate

Question 48

High level glutamate released by rods

Answer 48

Signal total darkness to bipolar cells

Question 49

Adaptation

Answer 49

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

Question 50

Which photoreceptors sensitivity increases due to convergence

Answer 50

Rods

Question 51

Rhodopsin in rods is composed of

Answer 51

Opsin + 11-cis-retinal

Question 52

Which one is the right pair?

Answer 52

L-cone and red/yellow light

Question 53

Which one is the beginning step of biochemical cascade of phototransuction

Answer 53

Photoisomerixation of rhodopsin

Question 54

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

Answer 54

CGMP

Question 55

Which one is a NT between rods and bipolar cells

Answer 55

Glutamate