physiology of the eye 4 Flashcards
what cells in the retina are first to receive information?
innermost photoreceptors
which cells in the retina exit the eye to carry information to the brain?
outermost cells
what is the direct (vertical) pathway for signal transmission?
photoreceptors -> bipolar cells -> ganglion cells -> axons of ganglion cells merge to form optic nerve
which cells receive input from photoreceptors and project to other photoreceptors and bipolar cells?
horizontal cells
which cells receive input from bipolar cells and project to ganglion cells, bipolar cells?
amacrine cells
what is the role of photoreceptors?
convert electromagnetic radiation to neural signals (transduction)
what are the 2 types of photoreceptors?
rods and cones
what is the structure of the photoreceptor? inferior to superior.
synaptic terminal
cell body
inner segment
outer segment
what is the difference between vertebrate photoreceptors and other neurons in terms of resting membrane potential?
vertebrate more negative resting MP
what happens to the membrane potential with light exposure?
hyperpolarizes (more +ve)
what causes this positive Vm?
dark current
cGMP-gated Na+ channel that is open in the dark closes in the light
what chain of events occur when the cGMP-gated Na+ channel closes in response to light?
PNA reduced -> greater efflux of K+ compared to influx of Na+ -> positive charged ions leave cell -> hyperpolarisation -> enables brain to perceive objects in the visual fields
what is the visual pigment molecule rhodopsin composed of?
retinal (vit A derivative) + opsin (GPCR)
what does light convert in rhodopsin?
11-cis-retinal to all-trans-retinal (activated form)
what does all-trans-retinal activate?
transducin -> molecular cascade -> decreases cGMP
activation of all-trans-retinal leads to what?
closure of cGMP-gated Na+ channel
lowered Na+ entry = hyperpolarization
what is visual acuity?
ability to distinguish between 2 nearby points, determined by photoreceptor spacing and refractive power
in terms of visual acuity when are cones used most/most powerful?
daylight
in terms of visual acuity when are rods used most/most powerful?
dim light
vision is blurry in dark
how are we able to see colour?
cones have different opsins for discrete wavelengths that allow perception of volour?
