vision Flashcards
macula
area of 95% of our vision
dark spot on eye images
when looking at a photo of the eye - what is the white spot
optical nerve
optical factors that affect VA
pupil size, refractive errors, clarity of optics
fovea
dense area of cones
centre of macula
where are there peak rods?
off-centre of macula
blind spot
no rods or cones
photopigments in rods & cones
rods: rhodopsin
(1 of 3): cone-opsins -> bind to Vit. A
vitamin A
receives signal & changes photopigment (like an antenna)
bound to rhodopsin & opsin
both rods and cones
phototransduction
photopigments have vitamin A attached
when light enters, 11-cis retinal becomes all-trans retinal (the kink straightens)
this results in a messenger cascade
rods vs cones
rods:
Night / BW vision
1 type
Absent from fovea
100 million
More sensitive
cones:
Day / Colour vision
3 types
Densest at fovea
5 million
Less sensitive
effect of light on photoreceptors
hyperpolarised
state of photoreceptors at night
depolarised due to continuous influx of sodium ions via cGMP
state of photoreceptors during day
cGMP -> GMP closes channel
No influx of sodium therefore hyperpolarised
passage of info within retina
photoreceptors -> bipolar cells -> ganglion cells
lateral interactions
horizontal cells (modify signal as it comes down, see things like flicker & edges)
amacrine cells
bipolar cells
2nd order cells
spatial & colour vision
ganglion cells
output cells of the retina
release glutamate via a.p. firing
ON ganglion cells
depolarise, send a.p. to brain
OFF ganglion cells
hyperpolarise, stops a.p. to brain
M ganglion
big (big r.f.)
target lateral
motion detection, flicker, gross features
P ganglion
small
visual acuity and colour
more numerous
receptive fields
(what do they do and how)
maximise edge detection
via. centre-surround organisation
lateral inhibition
(horizontal and amacrine)
what nt’s?
via. horizontal cells
provide output to photoreceptors
inhibitory NT GABA
respond to light by hyperpolarising
via. amacrine cells
glycine and gaba NTs
visual pathway
retina - optic nerve - lateral geniculate nucleus - optic radiations - V1
optic chiasm
fibres from right and left optic nerves combine
crossing of vision
L side of both eyes is processed at right side of brain
LGN
lateral geniculate nucleus
where in brain & what layers receive what input?
apart of the thalamus
layers 1-2: receive input from M
layers 3-6: receive input from P
ocular dominance columns
functions of neurons in layer 4C
orientation columns
neurons best respond to a certain orientation
organised like a box
M type to what layer
to layer 4Ca
P type to what layer
to layer 4CB
ventral vs dorsal in vision
dorsal: where in visual field
ventral: what are you seeing
ventral vs dorsal in vision
dorsal: where in visual field
ventral: what are you seeing
area MT
(processes what? input from where? retinotopic info from where?)
processing object motion
input from later 4B
Retinotopic info from V2 and V3
ventral stream
vision
V1, V2, V4
shape and colour perception
area IT
inferior temporal
ventral stream
major output of V4
visual memory and perception
perception of faces
