MODULE 6- The Visual System Flashcards
human visual system can detect only the ____ nm range of the entire electromagnetic spectrum
380-750 nm
how is visible light transmitted into the eye
some light source (e.g., sun, light bulb) emits light ->
to some object ->
light is reflected to our eyes
the wavelength corresponding to the color of the object we see is reflected/absorbed
reflected back to us
all other wavelengths that are not the color of the object we see are reflected/absorbed
absorbed
retina
-innermost layer of the eye
-contained > 100 million photoreceptors
ciliary body
contains a muscular component that shapes the lens
path of light
cornea ->
anterior chamber (aqueous humor) ->
pupil ->
lens ->
vitreous humor ->
fovea
projections of the visual field onto the ____
retina
what is in the center of the macula lutea
fovea
where is visual acuity the highest
fovea
scotoma
“blind spot”
scotoma (blind spot)
where the ganglion cell axons leave the eye + then become the optic nerve
there are no ____ in the scotoma (blind spot)
photoreceptors
visual field
the visual space that each eye sees
how is the visual field divided
-left + right sides (nasal + temporal halves)
-superior + inferior halves
overlap of the left + right visual fields gives ____
binocular depth perception
what causes image to be inverted (2)
cornea + lens
6 cell types in the retina
-rods + cones
-bipolar + horizontal cells
-amacrine cells
-retinal ganglion cells
rods + cones
photoreceptors in the outer nuclear layer
bipolar + horizontal cells
interneurons in the outer plexiform layer
amacrine cells
cell bodies in the inner nuclear layer
retinal ganglion cells
end cells in the inner plexiform layer
retinal ganglion cells axons exit the eye as the ____
optic tract
**quickest/most direct way for light transmission
cones/rods (photoreceptors) ->
bipolar cells ->
ganglion cells
the transmission of electrical signals in neurons propagates in the same/opposite direction of light
opposite
the tranmission of electrical signals in neurons propagates in the opposite direction of light via a ____
3-neuron chain
phototransduction
conversion of photons into electrical signals (transduced)
phototransduction is carried out by what
rods + cones
do rods + cones depolarize or produce APs
NO
light activation causes a graded depolarization/hyperpolarization of the membrane potential
hyperpolarization
light activation causes a graded hyperpolarization of the membrane potential which causes a change in what
the rate of neurotransmitter release onto postsynaptic neurons
pathway for cyclic GMP-gated channels + light-induced changes in the electrical activity of photoreceptors IN THE DARK
-cyclic guanosine monophosphate (cGMP) is in high concentration inside the cell
-cGMP binds to Na+ channels keeping them open
-allows Na to enter keeping membrane depolarized
pathway for cyclic GMP-gated channels + light-induced changes in the electrical activity of photoreceptors IN THE LIGHT
-cGMP concentration is reduced once light stimulates the region
-channels close
-leads to the receptor hyperpolarization
-both rhodopsin + opsin contain 11-cis-retinal ->
all-trans-retinal by a photon of light
-in the light, transducin: 2nd messenger activated -> PDE ->
cGMP hydrolyzed ->
closure of Na+ + Ca2+ channels
where are cones most highly concentrated
fovea
-then sharply decrease their numbers by as little as 10 degrees away
are there rods in the fovea
no
there are way more rods/cones numbers + density throughout the retina (besides the fovea)
rods
rods exhibit a high degree of ____
convergence
how many contacts does each cone have with a bipolar neuron
only 1 contact
rods/cones are much more sensitive
rods
how many photons does it take to activate a rod
1
how many photons does it take to activate a cone
greater than 100
rods have low/high spatial resolution
low
rods are/aren’t extremely light sensitive
are
rods operate well at low/high illumination levels
low
scoptopic vision
operating well at low illumination levels
rods are scoptopic/photopic
scoptopic
cones have low/high spatial resolution
high
cones are/aren’t sensitive to low light levels
aren’t