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
cones are highly sensitive to what type of light
bridge
photopic vision
highly sensitive to bright light
cones are scoptopic/photopic
photopic
human vision is ____-chromatic
trichromatic
trichromatic
3 different types of cones
human vision has how many different types of cones
3
how is a specific color detected
by comparing the activities of specific cones
____% of U.S. males are color blind
8%
-more prevalent in males
____% of U.S. females are color blind
1%
receptive field
whether in the retina or in the visual center in the brain, every neuron will respond to a presence or property of light within a confined visual space around it
receptive fields gain ____ with increased interactions with other neurons (e.g., bipolar cells) as distance from the retina increases
complexity
when does ON-center ganglion fire APs
when illuminated in the receptive field
when does OFF-center ganglion cell fire APs
when not illuminated (light is turned off)
agonistic/antagonistic center-surround arrangement of their receptive fields
antagonistic
ON + OFF pathways are in the ____
retina
**what is the difference between ON/OFF bipolar cells
different glutamate receptors
the different types of glu receptors for ON/OFF pathways allow cells to do what
respond to inrements + decrements in light levels
photoreceptors always depolarize/hyperpolarize
hyperpolarize
sign inverting (-)
if change in membrane potential of the bipolar cell is opposite of that in photoreceptor
sign conserving (+)
if the change in membrane potential is the same for the photoreceptor + bipolar cell
information supplied by retina (4)
- mediates the pupillary light reflex
- regulates circadian rhythms (day/night cycle)
- directs eyes to targets of interest
- leads to conscious perception of the visual scene
principle pathway for visual perception
retina ->
lateral geniculate nucleus in the thalamus ->
primary visual cortex
dinural
day/night
**information goes DIRECTLY from ____ to all BUT the ____
-retina
-striate cortex
hypothalamus function
regulation of circadian rhythms
-dinural
pretectum function
reflex control of pupil + lens
-pupil
superior colliculus function
orienting the movements of head + eyes
-eye movements
striate cortex function
perception
2 types of projections in the retino-geniculo-cortical pathway
-parallel
-retinotopic
what cells carry feature information to the brain
retinal ganglion cells
midget cells are also called
P cells
parasol cells are also called
M cells
midget (P cells)
project to 4 parvocellular layers of lateral geniculate
parasol (M cells)
project to 2 magnocellular layers of lateral geniculate
lateral geniculate receives input from the retina based on M/P cell type
both cell types
-and which eye (ipsilateral vs. contralateral)
**lateral geniculate axons terminate in eye-dependent ____
ocular dominance columns
lateral geniculate axons terminate in eye-dependent ocular dominance columns in ____ of primary visual cortex
layer 4
stereopsis
binocular depth perception
P cells have small/large receptive fields
small
M cells have small/large receptive fields
large
P cells have sustained/transient duration of response
sustained
M cells have sustained/transient duration of response
transient
do P cells transmit information about color
yes
do M cells transmit information about color
no
can P cells detect low-constrast stimuli
no
can M cells detect low-contrast stimuli
yes
fovea takes up ____% of retinal surface area
1%
fovea supplies ____% of visual information to the visual cortex
50%
the upper visual field is below the ____
calcarine sulcus
much of the cerebral cortex engages in what
higher-level processing by integrating the information arriving at the primary visual cortex
how many cellular layers of primary visual cortex
6
what layers of primary visual cortex hold pyramidal neurons
2, 3, 5, 6
what do pyramidal neurons do
release glutamate to subcortical + other cortical targets
what does layer 4 of primary visual cortex have
spiny stellate cells
layer 4 of the primary visual cortex is the primary target of what
extremely dense projecting axons from lateral geniculate
`
primary visual cortex has what type of arrangement
columnar
neurons within the same cortical column have the same/similar
receptive field properties + response preferences
preferred orientation
the orientation of a stimulus to which a cortical neuron maximally responds
preferred orientation is also called
peak of the tuning curve
neurons in the primary visual cortex response ____ to oriented edges
selectively
each class of orientation-selective neuron transmits what
only a small fraction of information in a scene
-the part that matches its filter properties
assembling the information from all these different filters contains what
all the spatial information necessary to create a representation of a scene
extrastriate visual areas
other cortical areas devoted to processing of information from the primary visual cortex
-hierarchial processing
extrastriate visual areas use ____ processing
hierarchial processing
ventral stream
recognizes the object/scene
“what?”
pathway of ventral stream
primary visual cortex ->
inferior tempoeral cortex
dorsal stream
analysis of motion + spatial relationships
-“where?”
pathway of dorsal stream
primary visual cortex ->
medial temporal area
patient with stroke in what is thought to be MT (visual motion processing area)
-had difficulty pouring tea in a cup
-fluid seemed to be frozen
-did no know when to stop because she was unable to perceive when the fluid had reached the brim
-had trouble sometimes following dialogue because she could not follow the movements of the speaker’s mouth
-could not cross streets easily- could not judge speed of approaching cars
-color + form intact
MT is specifically involved in what
processing visual motion
cerebral achromatopsia
-picture looks gray; may or may not be loss of acuity
-other aspects of vision are not working well
-when asked to draw an apple or school bus they cannot remember the appropriate color
what works fine in cerebral achromatopsia
cone receptors
cerebral achromatopsia is caused by damage to
extrastriate cortex (V4)
