3 - The Eye & Retina

Question 1

list the layers of the retina beginning with the photoreceptor layer

Answer 1

• photoreceptor layer
• outer plexiform lyer
• inner nuclear layer
• inner plexiform layer
• ganglion cell layer

Question 2

which layer of the retina sends signals to the brain?

Answer 2

ganglion cell layer

Question 3

the retinal vasculature of the eye supplies what?

Answer 3

the inner retina

Question 4

the choroidal vasculature of the eye supplies what?

Answer 4

the photoreceptors

Question 5

which vasculature of the eye is disrupted in glaucoma?

Answer 5

retinal

Question 6

which vasculature of the eye is disrupted by retinal detachment?

Answer 6

choroidal

Question 7

what is the role of photoreceptors?

Answer 7

transmit light into a biological signal

Question 8

what is the role of the inner nuclear layer/

Answer 8

extract visual information

Question 9

what is the role of the retinal ganglion cells?

Answer 9

transmits signal to the brain

Question 10

what does the outer segment of the photoreceptor contain?

Answer 10

plasma membrane

Question 11

what does the inner segment of the photoreceptor contain?

Answer 11

cilium
mitochondria
golgi

Question 12

what photopigment do photoreceptors contain?

Answer 12

rhodopsin

Question 13

what does rhodopsin contain?

Answer 13

retinaldehyde bound to opsin

Question 14

11-cis retinal is found in rhodopsin. what structural isoform is it converted into when light is absorbed?

Answer 14

all-trans retinal

Question 15

what is the opsin protein?

Answer 15

7 transmembrane domain G protein coupled receptor

Question 16

what is the function of opsin?

Answer 16

• amplifies isomerisation of retinal into a biological signal
• determines which wavelengths retinal absorbs

Question 17

how does 11-cis retinal react with opsin?

Answer 17

• acts as an inverse agonist
• keeps opsin inactive

Question 18

how does all-trans retinal react with opsin?

Answer 18

• acts as an agonist
• initiates signalling cascade

Question 19

outline the phototransduction cascade in 4 steps

Answer 19

• photon absorption - activates rhodopsin
• G-protein dissociation - separation of alpha, gamma, beta subunits
• alpha subunit activates cGMP into phosphodiesterase
• closure of cGMP-gated channels

Question 20

what happens to the polarity of a photoreceptor in the dark? how does this effect neurotransmitter release?

Answer 20

• depolarises
• releases lots of glutamate

Question 21

what happens to the polarity of a photoreceptor in the light? how does this effect neurotransmitter release?

Answer 21

• responds to light exposure with graded hyperpolarisation
• reduces glutamate releases

Question 22

why are rods used at night instead of cones?

Answer 22

• capture more photons
• have a larger signal amplification
• so are more sensitive

Question 23

which has a higher acuity - rods or cones?

Answer 23

cones

Question 24

which photoreceptor provides colour vision?

Answer 24

cones

Question 25

what photoreceptors does the fovea contain?

Answer 25

cones

Question 26

the peak absorption for retinal is normally ultraviolet, which humans can't see. what adaption changes this?

Answer 26

* retinal binds with opsin * changes relative sensitivity to wavelengths on a visible spectrum

Question 27

how many cone opsin genes are there?

Answer 27

3

Question 28

what creates colour vision?

Answer 28

* 3 cone opsin genes * long wave cone - red wavelengths * middle wave cone - green wavelengths * short wave cone - blue wave lengths

Question 29

what wavelength is associated with long-wave cones?

Answer 29

564nm - red

Question 30

what wavelength is associated with middle-wave cones?

Answer 30

533nm - green

Question 31

what wavelength is associated with short-wave cones?

Answer 31

433nm - blue

Question 32

photoreceptors translate the light intensity pattern into what?

Answer 32

a spatial pattern of glutamate release

Question 33

if its dark, is more or less glutamate released?

Answer 33

more

Question 34

what connects photoreceptors to retinal ganglion cells?

Answer 34

bipolar cells

Question 35

what are the 2 types of bipolar cell?

Answer 35

* sign inverting - "on" * sign conserving - "off"

Question 36

what glutamate receptors do sign inverting bipolar cells have? *what does this result in?*

Answer 36

* metabotropic * *glutamate activates signalling cascase* * *closes cation channels*

Question 37

what glutamate receptors do sign conserving bipolar cells have? *what does this result in?*

Answer 37

* ionotropic * cation channels are opened by glutamate

Question 38

are sign inverting bi polar cells depolarised or hyperpolarised by a flash of light?

Answer 38

depolarised - on

Question 39

are sign conserving bi polar cells depolarised or hyperpolarised by a flash of light?

Answer 39

hyperpolarised - off

Question 40

what is the role of horizontal cells?

Answer 40

connect neighbouring photoreceptors to amplify local differences in light intensity

Question 41

what happens to horizontal cells if there is a light spot?

Answer 41

* neighbouring cones are depolarised * horizontal cells are depolarised * signal from the centre cone to bipolar cell enhances

Question 42

what happens to horizontal cells in diffuse light?

Answer 42

* neighbouring cones are hyperpolarised * causes horizontal cells to be hyperpolarised * signal from centre cone to bipolar cells in dampened

Question 43

as well as enhancing light differences, what other role do horizontal cells have?

Answer 43

encode colour

Question 44

what happens to horizontal cells in red light?

Answer 44

* neighbouring cones become more hyperpolarised * horizontal cells are moe hyperpolarised * signal from centre cone to bipolar cells is reduced

Question 45

what happens to horizontal cells in green light?

Answer 45

* neighbouring cones are less hyperpolarised * horizontal cells are less hyperpolarised * signal from centre cone to bipolar cells is enhanced

Question 46

what is the role of amacrine cells?

Answer 46

provide an inhibitory link between bipolar cells and retinal ganglion cells