L27 The Retina Flashcards
what makes up the structure of the photoreceptors?
outer segment
inner segment
describe the outer segment of the photoreceptors
they are oriented towards the RPE
contain visual pigment for photoreceptor transduction
describe the inner segment of the photoreceptors
directed toward the inside/center of eyeball
forms synapses which transmit the visual info on the retinal cells (bipolar/horizontal cells)
what NT is released from retinal photoreceptors?
glutamate
is glutamate released in the light or dark?
dark - light reduces the release of glutamate
what is disk shedding?
the outer segment renews disks from the bottom up
the top disks are shed and phagocytozed by RPE cells
what is the main function of rods? describe the characteristics
to enable vision in the dark ->
cellular amplification mechanism is well developed which increases light sensitivity
temporal summation is poor (distinguish between 2 flashes of light)
convergence is high
only 1 type
what are the characteristics of cones
amplification is low = less sensitive to light
works better in bright conditions
3 different types of cones that allow color vision
convergence is low = increasing spatial resolution (visual acuity) showing better vision in the light
are rods and cones evenly distributed?
NO
NO rods in the FOVEA = no central vision in the dark
what is rhodopsin
the visual pigment of rods (2 components)
what are the 2 components of rhodopsin?
opsin
retinal
what is opsin
protein synthesized in the photoreceptor
have 7 membrane spanning domains
what is retinal
light absorbing compound derived from vitamin A and is the chromopore of the visual pigment
covalently attached to the 7th domain of opsin
what is the mechanism that occurs in the dark
visual pigment inactive– G-protein inactive – cGMP phosphodiesterase inactive – intracellular cGMP CAN gate the cGMP-gated Na+ channel to OPEN = depolarization — glutamate released
when do photoreceptors depolarize
in the dark
when do photoreceptors hyperpolarize?
in the light
what is the mechanism that occurs in the light
visual pigment active – G-protein (transducin) active – cGMP phosphodiesterase – metabolizes intracellular cGMP – close Na+ channel - hyperpolarize == stopping glutamate!