Case 3 - Structure and Function of the Eye and Retina

Question 1

what do the photoreceptors do

Answer 1

translate light into a biological signal

Question 2

what does the inner nuclear layer do

Answer 2

extract visal information e.g contrast

Question 3

what does the retinal ganglion cells (optic nerve) do

Answer 3

transmit that signal to the brain

Question 4

what is included in the vasculature

Answer 4

retinal: supplies the inner retina and disturbed in glaucoma

choroidal: supplies photoreceptors and dicstruured by retinal detachment

Question 5

what are photoreceptors

Answer 5

are neurones.

Question 6

describe the protein that absorbs light in photoreceptors

Answer 6

is a membrane associated protein and in the case of rods, it is rhodopsin

Question 7

what does light absorption rely on

Answer 7

an organic cofactor called retinaldehyde (retinal)

Question 8

what is retinal the derivative of

Answer 8

retinol or Vitamin A

Question 9

what are the two iso forms of retinal

Answer 9

• 11-cis retinal
• all-trans retinal

Question 10

how do they differentiate

Answer 10

differentiate between two carbons in the carbon chain
- the kink is no longer there in all-trans retinal

Question 11

diagram of the iso forms of retinal

Answer 11

Question 12

describe the opsin protein

Answer 12

7 transmembrane domain G protein coupled receptor

Question 13

what is the function of the opsin proteins

Answer 13

• amplify isomerisation of retinal into a ‘biological’ signal
• determines which wavelengths retinal absorbs

Question 14

what does the opsin protein translate

Answer 14

it translates photoisomerisation of retinal into a biological signal

Question 15

how does 11 cis retinal act

Answer 15

acts as an ‘inverse agonist
keeps opsin in inactive state

Question 16

how does all-trans act

Answer 16

is an agonist - initiates signalling

Question 17

what does signal amplification allow for

Answer 17

meaningful response to single photon absorption

Question 18

protein signal amplification diagram

Answer 18

Question 19

what do photoreceptors respond to light exposure with

Answer 19

graded hyperpolarisation. this results in a reduction in glutamate release at their synaptic terminals

Question 20

what do rods do vs cones

Answer 20

rods capture more photons and have a. larger signal amplification therefore mores sensitive

Question 21

features of cones

Answer 21

adjust their sensitivity to be activate under any light level.
- have a higher acuity
- provide colour Vision
- fovea is all cones

Question 22

how do photoreceptors absorb light

Answer 22

absorb light using 11-cis retinal bound to opsin protein

Question 23

what does photoisomerisation to all-trans retinal induce

Answer 23

structural change in opsin and activates G protein signalling cascade

Question 24

‘on’ vs ‘off’ responses to light

Answer 24

Question 25

what do horizontal cells do

Answer 25

provide lateral inhibition in the horizontal plane here at this layer between the photoreceptors and the bipolar cells

the horizontal cells link cones in a region of the retina

Question 26

diagram of horizontal cells

Answer 26

Question 27

horizontal cells - enhancing differences diagram

Answer 27

Question 28

horizontal cells - encoding colour diagram

Answer 28

Question 29

what do amacrine cells do

Answer 29

provide an inhibitory link between bipolar cells and RGCs … further modulation of response

Question 30

modulation at outer plexiform layer is by what cell

Answer 30

horizontal cell

Question 31

modulation at inner plexiform layer is by what cells

Answer 31

amacrine cells

Question 32

go over this lecture again to understand the concepts