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Flashcards in Photoreceptors Deck (32)
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1

Define Photoreceptor

cell specialised for light detection

2

what do photoreceptors contain?

photo-pigments

3

what are photopigments?

a protein and a light absorbing co-factor

4

what do photoreceptors allow us to do?

see by monitoring light originating from a particular point in visual space

5

what are photoreceptors in very simple eyes like?

a pigmented pit, limited direction from which the light can reach each receptor - can tell which direction light's coming from

6

what are photoreceptors like in the insect compound eye?

they're provided by neurons in the ommatidium (each unit in the compound eye) . pigmented cells in each ommatidium ensure light only reaches the photoreceptors through front opening of eye- not side. allows spatial resolution

7

What are photoreceptors like in mirror eyes?

the eyes are like concave mirrors that focus the image onto an array of photoreceptors (like a reflective telescope) light bounces onto the photoreceptors

8

What are are photoreceptors like in the lens eye?

each photoreceptor receives light from a different point in visual space- becoming an independent pixel for the image

9

where are photoreceptors found in the lens eye?

the retina

10

what are the photoreceptors in vertebrate eyes?

rods and cones

11

where does the light go to first when it reaches the retina?

photoreceptors

12

what's the photopigment in cones?

Opsin

13

What's opsin made up from?

an opsin protein + chromophore

14

what is a chromophore?

a co-factor that absorbs light and retinaldehyde

15

what does light do to retinaldehyde?

transforms it from 11-cis to all-trans retinaldehyde (2 different isoforms)

16

describe the structure of the opsin protein

a GPCR (7 transmembrane domains)

17

what does the opsin protein bind?

retinaldehyde

18

what does the opsin do?

translates the isomerisation of retinaldehyde into a biological signal that determines the wavelengths that the retinaldehyde absorbs

19

what happens when retinaldehyde binds Opsin

dissociation of Ga and GbGy. Both these subunits bind to effector enzymes to produce second messengers like cAMP (the all-trans retinaldehyde is a ligand)

20

does light activate or inhibit retinaldehyde?

Activate

21

describe the transduction cascade

Opsin (GPCR) is affected by light so can interact with transducing GP to activate the second messenger cGMP phosphodiesterase
this is reduced to cause the opening of cGMP gated channels
allows Na+ to flood in- positive charge
depolarisation of photoreceptor
this remains until cGMP is reduced and channels close

22

what's the minimum number of photons rods can detect?

a single photon (1)

23

a photoreceptors depolarised in the light or dark?

dark

24

How does light/dark affect the glutamatergic synapse?

in the dark there's therefore more glutamate released (due to depolarisation)- and vice versa for light

25

what captures more photons, rods or cones?

rods

26

what has a larger signal amplification. rods or cones?

rods

27

what's more sensitive to light, rods or cones?

rods

28

in what light conditions are rods used?

dim light

29

can cones adjust their sensitivity?

yes

30

what light conditions are cones used?

more under bright conditions but adjust sensitivity to be used under any light conditions

31

what type of vision do cones provide?

colour

32

what is the fovea made up of?

all cones (why we have the highest acuity in central vision)