Flashcards in Vision I, II, and III Deck (50):
The aqueous humor is in the ____________, while the vitreous humor is in the _____________.
eye compartment anterior to the lens; eye compartment posterior to the lens
What two parts of the eye focus light?
The cornea (2/3) and lens (1/3); this allocation is what allows ophthalmologists to perform laser correction.
The zonule fibers connect what to what?
The zonule fibers connect the lens to the ciliary muscle
Lenses focus what colors of light better?
Red and green
There are five types of cells in the reina. Briefly describe each.
1). Photoreceptors (rods and cones)
2). Bipolar cells (on/off)
5). Ganglion (output neurons that leave the eyeball)
* The first four types do not fire action potentials.
The vertical flow of information through the retina proceeds through what cells?
Photoreceptor -> bipolar cells -> gaglion
The horizontal flow of information through the retina is mediated by _____________.
horizontal cells and amicrine cells; they communicate what neighboring cells are doing
How many rods and cones are in each eye?
The fovea is predominantly ___________.
In the center of the retina, photoreceptors are in a _______ ratio with ganglion cells; in the periphery, however, the ratio is ___________.
1 photoreceptor : 1 ganglion cell
1 photoreceptor : many ganglion cells
Rhodopsin = ___________ + _____________.
opsin (a 7 transmembrane G protein); retinal (light sensitive molecule)
On-ganglions have both a positive center and an __________ periphery. Off-ganglions have the opposite.
inhibitory (the area around it can actually inhibit the ganglion if stimulated)
______________ are another form of stimulation for the inhibitory cells of the ganglion.
Rebound signals (action potentials that occur when the inhibitory area ceases to be stimulated)
Uniform stimulation (that is, both center and periphery) is not a good stimulator of on-off ganglion receptor fields. Why?
Because those areas detect contrast
Horizontal cells use the inhibitory transmitter _________. How does this affect their target cells?
GABA; it further hyperpolarizes the photoreceptors
Describe the anatomy of the lateral geniculate nucleus.
It is a horseshoe-shaped, six-layered complex. The layers are numbered from bottom to top (with 1 on the bottom).
Which layers of the LGN are from the contralateral eye?
1, 4, and 6
Cells in layers _______ are large.
1, 2 (these are the magnocellular layers)
Layers 3 - 6 are referred to as the ___________.
The magnocellular layers sense ________.
motion and depth
The parvocellular layers sense __________.
color, form, and fine detail
The primary visual cortex (V1) is Brodmann's area _____.
Topographically, the upper visual field is __________ to the calcarine fissurer. The retinal center is most _________.
Input to the cortex from the lateral geniculate nucleus arrives at what cortical layer?
Binocular vision occurs at the level of the ________.
cortex; there is no mixing or synthesizing information at the lateral geniculate nuclei
The right hemisphere process information from which sides of the retinas?
Right, because the right sides of the retinas capture light coming from the left visual field, and the right hemisphere process left-visual-field information
Describe Hubel and Wiesel's findings on binocular cells in the cortex.
They assigned cells a value of 1 - 7; neurons that only responded to signals from the left eye were given a score of 1, while neurons that only responded to signals from the right eye were given a score of 7. Cells that required bilateral stimulation received a score of 4. Hubel and Wiesel found that roughly 80% of the cells in the cortex are binocular.
True or false: monocular deprivation leads to blindness in children.
True! As does binocular deprivation
Hubel and Wiesel demonstrated that ___________ is necessary for binocular cells in the cortex to develop.
simultaneous bilateral stimulation
When, in the age of the individual, does the deprivation effect cease to happen?
About 2-3 years; it's much less in cats – only 16 weeks. Researchers think that the sensitive period is longer in humans because our heads take longer to achieve their adult sizes. As the head grow, the distance between the eyes increases, thus changing the angle between the eyes and a given focal distance.
What wavelength can the photoreceptors of the eye detect?
400 nm - 700 nm
True or false: the posterior chamber of the anterior eye contains the vitreous humor.
False! There are two compartments of the anterior eye, both of which contain aqueous humor.
Only the ___________ neurons (in the retina) make action potentials.
ganglion (all others – the photoreceptors, bipolar cells, horizontal cells, and amacrine cells – engage only in passive electrical diffusion)
What evidence demonstrates that the retina processes light?
There are 100x as many photoreceptors as ganglionic axons.
What determines the type of receptor field (e.g., on-center, linear, etc.)?
The type of bipolar cell! Some are excited by the glutamate secreted by photoreceptors, while some are inhibited by glutamate.
Hyperpolarization results in less or more neurotransmitter being released?
What neurotransmitter do photoreceptors secrete?
Horizontal cells behave as though they have __________ receptors.
excitatory glutamate (meaning they excite other cells when they touch glutamate from photoreceptors)
The lateral geniculate nucleus is within what structure?
Axons from the ____________ side of each eye cross at the chiasm.
Cells in the _________cellular system contain information about movement, spatial layout, and crude outline.
All cells in a central column are sensitive to ___________.
the same orientation of light
Simple cells have orientation fields that are ______________.
Complex cells account for ________________.
There are two pathways of visual information from the V1 area of the cortex: _______________.
dorsal (from V1 to the parietal cortex, being spatial information) and ventral (from V1 to the temporal cortex, being object information)
The middle temporal cortex is also called _______ and is sensitive to __________. Where pathway leads here?
V5; motion direction; dorsal
In accommodating for near objects, the lens gets __________.
What is transducin?
The G protein that activates PDE
The on-center / off-center distinction occurs at the level of the ____________.
ganglion cells (because they receive input on the different fields)