3 - The Eye & Retina Flashcards
list the layers of the retina beginning with the photoreceptor layer
- photoreceptor layer
- outer plexiform lyer
- inner nuclear layer
- inner plexiform layer
- ganglion cell layer
which layer of the retina sends signals to the brain?
ganglion cell layer
the retinal vasculature of the eye supplies what?
the inner retina
the choroidal vasculature of the eye supplies what?
the photoreceptors
which vasculature of the eye is disrupted in glaucoma?
retinal
which vasculature of the eye is disrupted by retinal detachment?
choroidal
what is the role of photoreceptors?
transmit light into a biological signal
what is the role of the inner nuclear layer/
extract visual information
what is the role of the retinal ganglion cells?
transmits signal to the brain
what does the outer segment of the photoreceptor contain?
plasma membrane
what does the inner segment of the photoreceptor contain?
cilium
mitochondria
golgi
what photopigment do photoreceptors contain?
rhodopsin
what does rhodopsin contain?
retinaldehyde bound to opsin
11-cis retinal is found in rhodopsin. what structural isoform is it converted into when light is absorbed?
all-trans retinal
what is the opsin protein?
7 transmembrane domain G protein coupled receptor
what is the function of opsin?
- amplifies isomerisation of retinal into a biological signal
- determines which wavelengths retinal absorbs
how does 11-cis retinal react with opsin?
- acts as an inverse agonist
- keeps opsin inactive
how does all-trans retinal react with opsin?
- acts as an agonist
- initiates signalling cascade
outline the phototransduction cascade in 4 steps
- photon absorption - activates rhodopsin
- G-protein dissociation - separation of alpha, gamma, beta subunits
- alpha subunit activates cGMP into phosphodiesterase
- closure of cGMP-gated channels
what happens to the polarity of a photoreceptor in the dark? how does this effect neurotransmitter release?
- depolarises
- releases lots of glutamate
what happens to the polarity of a photoreceptor in the light? how does this effect neurotransmitter release?
- responds to light exposure with graded hyperpolarisation
- reduces glutamate releases
why are rods used at night instead of cones?
- capture more photons
- have a larger signal amplification
- so are more sensitive
which has a higher acuity - rods or cones?
cones
which photoreceptor provides colour vision?
cones
what photoreceptors does the fovea contain?
cones
the peak absorption for retinal is normally ultraviolet, which humans can’t see. what adaption changes this?
- retinal binds with opsin
- changes relative sensitivity to wavelengths on a visible spectrum
how many cone opsin genes are there?
3
what creates colour vision?
- 3 cone opsin genes
- long wave cone - red wavelengths
- middle wave cone - green wavelengths
- short wave cone - blue wave lengths
what wavelength is associated with long-wave cones?
564nm - red
what wavelength is associated with middle-wave cones?
533nm - green
what wavelength is associated with short-wave cones?
433nm - blue
photoreceptors translate the light intensity pattern into what?
a spatial pattern of glutamate release
if its dark, is more or less glutamate released?
more
what connects photoreceptors to retinal ganglion cells?
bipolar cells
what are the 2 types of bipolar cell?
- sign inverting - “on”
- sign conserving - “off”
what glutamate receptors do sign inverting bipolar cells have? what does this result in?
- metabotropic
- glutamate activates signalling cascase
- closes cation channels
what glutamate receptors do sign conserving bipolar cells have? what does this result in?
- ionotropic
- cation channels are opened by glutamate
are sign inverting bi polar cells depolarised or hyperpolarised by a flash of light?
depolarised - on
are sign conserving bi polar cells depolarised or hyperpolarised by a flash of light?
hyperpolarised - off
what is the role of horizontal cells?
connect neighbouring photoreceptors to amplify local differences in light intensity
what happens to horizontal cells if there is a light spot?
- neighbouring cones are depolarised
- horizontal cells are depolarised
- signal from the centre cone to bipolar cell enhances
what happens to horizontal cells in diffuse light?
- neighbouring cones are hyperpolarised
- causes horizontal cells to be hyperpolarised
- signal from centre cone to bipolar cells in dampened
as well as enhancing light differences, what other role do horizontal cells have?
encode colour
what happens to horizontal cells in red light?
- neighbouring cones become more hyperpolarised
- horizontal cells are moe hyperpolarised
- signal from centre cone to bipolar cells is reduced
what happens to horizontal cells in green light?
- neighbouring cones are less hyperpolarised
- horizontal cells are less hyperpolarised
- signal from centre cone to bipolar cells is enhanced
what is the role of amacrine cells?
provide an inhibitory link between bipolar cells and retinal ganglion cells
