ELM 7.1 Flashcards
The component of the eye that produces the greatest refraction is the:
cornea
the cornea accounts for about 2/3 of the refractive power of the eye - large degree of refraction produced by the cornea is because light enters it from a gaseous phase
A visual protein is composed of one molecule each of
opsin and retinal
the visual proteins are members of the retinylidene protein family
in vertebrates, the members of this family are the G protein coupled receptors
the retinal can be regarded as a light activated agonist of the receptor - when it is struck by light of the correct wavelength, the retinal undergoes an isomerisation from cis to trans form (in vertebrates)
the wavelength of light that the retinal is sensitive to depends on the exact amino acid sequence of the opsin protein that is present
To which group of proteins does rhodopsin belong?
g protein coupled receptors
rhodopsin is a member of the g protein coupled receptor superfamily - 7 transmembrane domains
mice with inactive melanopsin genes would have disturbances in their
circadian rhythm
melanopsin the visual pigment present in photosensitive ganglion cells
these cells are involved in the pupillary reflex and in entrainment of circadian rhythms to light and dark periods - not invovled in vision
the primary visual cortex is located in which lobe?
occipital
the sequence of events that occurs following light exposure of a vertebrate rod/cone photoreceptor is: (opsin activation, closure of cGMP-gated chennels, depolarization/hyperpolarization)
opsin activation, closure of cGMP-gated channels, hyperpolarization
light may be described both as an _______ and as a bunch of _____
electromagnetic wave
photons
large amplitude means ___ light
bright
myopia
short-sightedness
hyperopia
far-sightedness
What kind of lens do you need for myopia?
concave
what kind of lens do you need for hyperopia?
convex lens
what order from outside to in
rods
horizontal cells
cones
amacrine cells
bipolar cells
retinal ganglion cells
rods
cones
horizontal cells
biopolar cells
amacrine cells
retinal ganglion cells
glutamatergic excitatory neurons
rods
cones
bipolar cells
retinal ganglion cells
RPE
pigmented layer at the back of the retina
what is RPE essential for?
recycling of retinaldehyde, thus maintaining function of rods and cones
helps rods and cones to cope with oxidative stress
most cones are in the _____ where we have max _____. this area is blind at ______
fovea
visual activity
night
what is the role of rods
night vision and peripheral vision
which are more sensitive - rods or cones?
rods - 1000 times more sensitivie
describe opsin
GPCR with 7 transmembrane domains
different opsins in 3 types of cones, rods, and melanopsin RGCs (5 opsins)
retinal (_____ for every opsin) describe
same
vitamin A derivative
absorbs light and changes conformation (bleaching)
in the dark, photorecptors are ______ when _____ are open
depolarized
sodium channels
in the light, _______ close, leading membrane ______
sodium ion channels
hyperpolarization
when the membrane is depolarized, there is _____ release
glutamate
_____ absorbs light and changes conformation. this results in the ______ of sodium channels and _______
retinal
closure
hyperpolarization
what is the order of these things ?
1 photon of light
2 activation of transducin
3 reduction in cGMP
4 closure of sodium channels
5 conformational change in rhodopsin molecule
6 activation of phosphodiesterase
1, 5, 2, 6, 3, 4
describe horizontal cells (3)
light intensity adaptation
spatial processing
colour processing (opponency)
describe amacrine cells (4)
- directional motion
- modulate light adaptation
- modulate circadian rhythm
- sensitivity of night vision
describe retinal ganglion cells RGC (3)
- further process colour, motion, and shapes
- the ONLY output cells, fire action potentials
- some RGCs (intrinsically photosensitive retinal ganglion cells) can detect light via melanopsin
melanopsin doesn’t contribute to image formation, but affects: (3)
- circadian rhythms
- pupil size
- body temp
