Case 3 - Structure and Function of the Eye and Retina Flashcards
what do the photoreceptors do
translate light into a biological signal
what does the inner nuclear layer do
extract visal information e.g contrast
what does the retinal ganglion cells (optic nerve) do
transmit that signal to the brain
what is included in the vasculature
retinal: supplies the inner retina and disturbed in glaucoma
choroidal: supplies photoreceptors and dicstruured by retinal detachment
what are photoreceptors
are neurones.
describe the protein that absorbs light in photoreceptors
is a membrane associated protein and in the case of rods, it is rhodopsin
what does light absorption rely on
an organic cofactor called retinaldehyde (retinal)
what is retinal the derivative of
retinol or Vitamin A
what are the two iso forms of retinal
- 11-cis retinal
- all-trans retinal
how do they differentiate
differentiate between two carbons in the carbon chain
- the kink is no longer there in all-trans retinal
diagram of the iso forms of retinal
describe the opsin protein
7 transmembrane domain G protein coupled receptor
what is the function of the opsin proteins
- amplify isomerisation of retinal into a ‘biological’ signal
- determines which wavelengths retinal absorbs
what does the opsin protein translate
it translates photoisomerisation of retinal into a biological signal
how does 11 cis retinal act
acts as an ‘inverse agonist
keeps opsin in inactive state
how does all-trans act
is an agonist - initiates signalling
what does signal amplification allow for
meaningful response to single photon absorption
protein signal amplification diagram
what do photoreceptors respond to light exposure with
graded hyperpolarisation. this results in a reduction in glutamate release at their synaptic terminals
what do rods do vs cones
rods capture more photons and have a. larger signal amplification therefore mores sensitive
features of cones
adjust their sensitivity to be activate under any light level.
- have a higher acuity
- provide colour Vision
- fovea is all cones
how do photoreceptors absorb light
absorb light using 11-cis retinal bound to opsin protein
what does photoisomerisation to all-trans retinal induce
structural change in opsin and activates G protein signalling cascade
‘on’ vs ‘off’ responses to light
