Vision Flashcards
________ connect the lens to the ciliary muscle
zonule fibers
The cornea provides ______ of the
refractive (or focusing) power for the eye,
while the lens provides only ______.
~2/3,
~1/3.
_________ capture photons of light and convert (transduction) them to an electrical signal (change in membrane potential), which is passed synaptically to , _______ & ________ and then to the
output cells of the retina, the ganglion cells
Photoreceptors (rods and cones),
bipolar cells and horizontal cells
Cones mediate _____ vision, are concentrated in the fovea, and work well only in ______ light. Rods are
color insensitive and work best in dim light
color,
bright
______ are the dominant photoreceptor away from the
fovea
rods
Humans have about ______rods and ______ cones in each retina
100 million,
8 million
in the dark photoreceptors have a relatively high
concentration of ______ which binds to and holds opens nonselective cation channels
cyclic GMP (cGMP),
Ganglion cells have donutshaped
receptive fields and come in two opposite types
Some are excited by light shining
in their centers and inhibited by light in the periphery called _________. Others are the
opposite called ________.
(‘on’ center ganglion cells)
‘off ‘ center ganglion cells
Bipolar cells can be either excited as in _____ or inhibited as in _____ by glutamate (due to different receptor types)
(OFF-center),
ON-center
Bipolar cells always make ________ synapses on ganglion cells
excitatory
Horizontal cells have excitatory receptors for _______released from photoreceptors, and make
_______ synapses on the neighboring photoreceptors in the field center
glutamate,
inhibitory
the LGN represents the _______
visual field
contralateral
Beyond the LGN, axons involved in
visual processing fan out in the ______ to the
visual cortex at the back of the brain
optic radiations
the lower half of each retina (which
‘sees’ the upper half of the visual world) projects to the
______of each visual cortex (the lower bank of the
calcarine sulcus)
lower half
Layers 1, 4, and 6 of LGN receive inputs from the ________ eye (these inputs desiccate at the chiasm)
contralateral
layers 2, 3, and 5 of the LGN receive inputs from the ________ eye. (these inputs desiccate at the chiasm)
ipsilateral
There is also a secondary segregation of information in the 6 layerspf LGN: Layers 1 and 2
receive inputs from the so-called ________while layers 3-6 receive inputs from the so-called _______.
magnocellular ganglion cells,
parvocellular ganglion cells.
what does the Parvocellular System detect?
Object Vision – color, form, detail
what are the 4 response properties of the Parvocellular System?
- High acuity (fine detail)
- Small receptive fields
- Not responsive to motion
- Color vision (input from cones)
what are the 4 response properties of the Magnocellular System?
- Low acuity (crude form)
- Large receptive fields
- Responsive to motion
- No color vision (input from rods)
thee foveal region, which occupies a tiny
fraction of the retina, occupies nearly ______ of the visual cortex
one-half
each hypercolumn is divided in two parts, one half for each eye; these are called ______
ocular dominance columns
describe hierarchical processing
Several cells with similar but spatially offset receptive fields converge on a higher order cell to create an altogether new type of receptive field.
what is the receptor field shape of a simple cell?
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