The eye and visual system Flashcards
visual light range
400-700 nm
what color is higher energy visable light
blue (400nm)
what color is lower energy visible light
red (700nm)
pupil
where light enters the eye
iris
controls the size of pupil/ how much light enters the eye
optic nerve
bundle of axons at the back of eye
extraocular muscles
muscles in eye that help eye focus
retnia
light receptive part of eye; contains light sensitive cells
fovea
part of retina with highest visual acuity/ most sensitive
optic disk
blind spot with no photoreceptors ; axons from ganglion cells leave the retina here to form the optic nerve
visual angle
measure size of objects in visual field
tan(theta) = S/D
what are the layers of the retnia
outer nuclear layer, inner nuclear layer, ganglion cell layer -> optic nerve
which cells in the retina can send action potentials
only ganglion cells; long distance signal sending
what are the cells in retnia
photoreceptor cells, horizontal cell, bipolar cell, amacrine cell, ganglion cells -> optic nerve
what are the 2 types of photoreceptor cells
rods and cones
rods
sensitive to light; good for night vision
cones
need more light to be active; daytime and color vision
why are photoreceptor cells light sensitive
contain light sensitive pigments
light sensitive pigments
opsins
*rods: redopsins
how do photoreceptor cells activate bipolar cells
action potential -> glutamate (excitatory)
what photoreceptor cells are in the fovea
many cones (high acuity vision) and no cones
rod pathway
provide converging input to bipolar cells to amplify visual input to ganglion cells under low light conditions
cone pathway
fovea cones may provide one to one input to bipolar cells to provide visual detail and color
convergence
amplify weak signals from photoreceptors to ganglion cells
which pathways have convergence
temporal and nasal periphery
which pathway does not have convergence
central retina
foveal pit
light directly to photoreceptor cells; provides light a clear path to photoreceptor to reduce light scattering
what features improve visual resolution at fovea
foveal pit, all cones no rods, no blood vessels at fovea
when is photoreceptor cell hyperpolarized
in the light (resting)
when is photoreceptor cell depolarized
in the dark
photoreceptor graded transmitter release
release of the neurotransmitter glutamate in response to light; proportional to photoreceptor depolarization
why do photorecepotr cells depolarize in dark
cGMP bind to Na+ receptor, Na+ in cell, depolarization
why are cells hyperpolarized in light
light activates phospodiesterase which breaks down cGMP and Na+ channel closes
on center cell
cell responds well to light in the center of the receptor fields but not the surround
on center cell glutamate receptor
mGluR6
off center cell
cell responds well to light in the surrounding of the receptor field but not in the center
off center cell glutamate receptor
AMPA/ kainate
on center ganglion cells
respond to luminous/light contrast by detecting light in middle of receptive field; identify edges
off center ganglion cells
respond to light on outside of receptive field
ganglion cells contrast sensitivity
sensitive to contrast; respond little with change in brightness over a large area
on/off center ganglion cell complementary response
respond most to light/dark contrast patterns across receptive field; useful for responding to/ detecting edges
3 types of cones (+their colors)
short wavelength (blue)
medium wavelength (green)
long wavelength (red)
trichromacy theory
humans perceive color by mixing three primary colors of light: red, green, and blue
color opponency
we process opponent colors in 2 channels; red-green channels and blue-yellow channels
additive color mixing
a process that combines light from multiple sources to create new color
5 types of color-opponent ganglion cells
red on-center, green off-surround
red off-center, green-on surround
green on-center, red off-surround
green off-center, red on-surround
blue on-center, yellow off-surround
color opposites
blue/yellow
green/red
black/white
3 opponent channels that carry info from retina to V1
chromatic channels (red/green and blue/yellow) and luminance channel (black/white)
2 classes of channels that carry info from retina to V1
chromatic and luminance
3 main types of retinal ganglion cells that project to thalamus
parasol cells (M type)
midget cells (P type)
small bistratified cells
parasol cells (M type) pathway and channel
magnocellular pathway; luminance channel
midget cells (P type) pathway and channel
parvocellular pathway; red/green chanel
small bistratified cells pathway and channel
koniocellular pathway; blue/yellow chanel
temporal hemiretina
the half of the retina that’s closest to the temple
nasal hemiretnia
the half of the retina that’s closest to the nose
what path does the right visual hemifield follow
left optic tract
what path does the left visual hemifield follow
right optic tract
optic chiasm
he part of the brain where the right and left optic nerves cross
what type of system is the visual system
contralateral
where do visual inputs go from the optic tract
LGN (lateral geniculate nucleus) in the thalamus
structure of the LGN
6 layers
which layers of the LGN recive inputs from the same side as the eye (ex. inputs from left eye to left LGN)
layers 5,3,2
which layers of the LGN recive inputs from the opposite side as the eye (ex. inputs from left eye to right LGN)
layers 1,4,6
magnocellular pathway
black/while luminance magnocellular cells (M type) send information to layers 1 and 2 of the LGN
parvocellular pathway
red/green parvocellular cells (P type) send info to layers 3-6 of LGN
koniocellular pathway
small bistratified cells send info the koniocellular cells in LGN (thin layers ventral to each principle layer)
function of parvocellular cell layer
process form and color info
function of koniocellular cell layer
process color info
function of magnocellular cell layer
process motion and depth info
where does the magnocellular pathway project to
4C alpha layer in V1
where does the parvocellular pathway project to
4Cb beta layer in V1
where does the koniocellular pathway project to
layers 1-3 in V1
what is another name for V1
primary visual cortex or striate cortex
why is V1 called the striate cortex
lots of axons from LGN -> V1 and form a stripe / striate
how is input mapped onto V1
ex.
L. M. R
M. R L. M
ocular dominance columns
stripes of neurons in the primary visual cortex (V1) that preferentially respond to input from one eye or the other.
what area best responds to oretiton of lines
V1
how are V1 cells organized for orientation selectivity
vertical (cortical column): all cells have same preferred orientation
horizontal (electrode track): cells all down the electrode tract have different prefered orientation that systematically changes (covers all possible orientation to represent all of visual space)
direction selectivity of V1 cells
cells respond when stimulus moves left to right
v1 receptive field
rectangle receptive field
simple cell
rectangle receptive field with on/off subregions
complex cell structure
no distinct on/ off region structure, comprised of many simple cells
complex cell preferred orientation
preferred orientation BUT it does not matter where in the receptive field the stimuli is
blobs
spots of conentrations of enzyme cytochrome oxidase that contribute to color processing
what layers for V1 are blobs in
layers 2 and 3 and laters 5 and 6
module
section that is capable of analyzing every aspect of a portion of visual field
what is in a V1 module
- orientation columns spanning 360 degrees of orientation
-ocular dominance columns from each eye
-many modules that overall cover the while visual field
where does V2 send info to
V3
where does V3 send info to
V4 and/or medial temporal (MT) area
where does V4 send into to
inferior temporal cortex -> anterior temprol cortex
where does the medial temporal area send info to
medial temporal area -> parietal areas
what do V2 cells respond to
preferred angles
what do V4 cells respond to
shape/ curve and color
what does the medial temporal area respond to
stimuli moving in particular directions; perception of motion
what is another name for the medial temporal area (MT)
V5
