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171 Cards in this Set

  • Front
  • Back
Where do blood vessels enter the eye?
The Optic Disk
There is a blind spot for the visual field of each eye. Why?
The optic disk has no photo receptors.
What region of the retinal receptor field has the highest acuity?
The fovea.
Where is the fovea?
In the center of the macula lutea.
Why is there such high acuity in the fovea?
High receptor numbers and displacement of the inner cell body layers away from the center.
Name the five different cell types in the retina.
Photoreceptors, bipolar cells, ganglion cells, horizontal cells, and amacrine cells.
What layer of the retina are photoreceptors in?
Outer Layer.
Photoreceptors synapse onto bipolar and horizontal cells in what layer of the retina?
Outer plexiform layer.
Bipolar cells are in what area of the retina?
Inner Layer
What cell types are included in the inner cell layer?
Bipolar, horizontal, and amacrine cells.
What cells synapse on each other in the Outer plexiform layer?
Photoreceptors, bipolar cells, and horizontal cells.
What cells synapse on each other in the Inner plexiform layer?
Bipolar, amacrine, and ganglion cells.
What level of sensitivity and specialization do Rods have?
High Sensitivity and Night Vision
How do Rods capture more light?
They have more photopigmentation.
How many photons are required to hyperpolarize a single Rod cells?
A single photon will hyperpolarize a Rod cell
What is the temporal resolution and integration time of a Rod cell?
Low Temporal Resolution and Long Integration Time.
The Rod System has what acuity?
Low Acuity
Give two reasons for the low acuity of the Rod System.
Not present in the central fovea. Highly convergent retinal pathway.
Which photoreceptor cell type is color sensitive?
Cone cells.
Why are Rod cells not color sensitive?
They have only one type of pigment.
What sensitivity and specialization do Cone photoreceptor cells have?
Low sensitivity and Day Vision.
Why is there a difference between the sensitivity of Rods and Cones?
Cones have less photopigmentation.
What is the temporal resolution and integration time of a Cone photoreceptor cell?
High Temporal Resolution because they are fast acting with short integration time.
Where are Cone Receptors most sensitive?
The axial rays.
What is the acuity of the Cone cell System?
High Acuity.
Why does the Cone system have such high acuity over the Rod system?
The cone system has cells in the fovea. The Cone System has cells with dispersed retinal pathways.
How many types of Cone cells are in the Cone System?
There are three types of pigment. Each sensitive to a different portion of the visual light spectrum.
Give the most direct pathway through the retinal system.
Photoreceptor cell to bipolar cell to ganglion cell.
Describe Phototransduction.
Absorption of light by photo pigment in the outer segment of the photoreceptor cell initiates a cascade that changes the membrane potential of the receptor cell, changing the rate of neurotransmitter release.
When a photoreceptor absorbs light, what happens to the membrane potential?
Hyperpolarization.
The Outer Nuclear Layer of the Retina is made up of what cells?
Photoreceptor cells.
What is included in the Outer Plexiform Layer of the Retina?
Synapses of photoreceptors on horizontal bipolar cells.
The Inner Nuclear Layer of the Retina is made of what cells?
The cell bodies of bipolar and horizontal cells as well as amacrine cell bodies.
What is included in the Inner Plexiform Layer of the Retina?
Short axons from the bipolar cells onto amacrine dendrites and the dendrites of ganglion cells.
What layer of the retina is closest to the center of the eye? Which layer is the first reached by light entering from the pupil?
The Ganglion Layer.
What two cell types in the retina enable lateral transmission?
Horizontal and Amacrine cells.
Which cell type in the Retina enable lateral interactions between photoreceptors and bipolar cells?
Horizontal Cells.
Which cell type in the retina is thought to maintain visual sensitivity to contrast over a wide range of intensities?
Horizontal Cells.
Amacrine cells are post-synaptic to and pre-synaptic to what cells? Two different cell types.
Bipolar and Ganglion Cells.
Amacrine cells are thought to have a part in the direction selectivity responses exhibited by which cells?
Ganglion Cells.
Which cells in the most direct path through the Retina do not produce action potentials?
Photoreceptor cells (Rods and Cones) and Bipolar Cells.
How does a photoreceptor cell react to light stimulus? Basic, do not go into phototransduction reactions.
Light causes a graded increase of membrane potentiation, hyperpolarization.
In the dark, what is the state of a photoreceptor cell?
Depolarized.
What is the saturation voltage of a photoreceptor cells (Rod)?
-65mV
Describe the photoreceptor actions in the dark.
The photoreceptor is depolarized, the number of Ca2+ receptors open in the synaptic terminal is high, and neurotransmitter release is high.
Sensitivity of Photoreceptor Cells.How many photons does it take to get a response from a Rod Cell and how many for a Cone cell?
A Rod photoreceptor cell can detect single photons. A cone can take up to one hundred photons to elicit a response.
How do rods and cones differ in their reaction to sustained light?
An individual cone does not saturate at high levels of steady illumination.
How many Rod Photoreceptor Cells converge onto a single Rod bipolar cell?
From 15 to 30.
How does the convergence of Rod photoreceptor cells onto single Rod Bipolar cells influence spatial resolution?
It decreases spatial resolution, because, for any given rod bipolar cell, you can not be certain where the excitation came from.
How many Cone Photoreceptor Cells converge onto a single Cone Bipolar cell?
There is roughly a one to one ration of cone photoreceptor cells to cone bipolar cells.
What is the pathway through the Retina for a Rod photoreceptor response?
Rod photoreceptor cells synapse onto Rod Bipolar cells, which synapse onto amacrine cells. Amacrine cells make gap junctions with cone bipolar cells. Cone bipolar cells synapse onto ganglion cells.
What is the relative amount of Cones photoreceptor cells in the retina with respect to the amount of Rods photoreceptor cells?
The number of Rod Photoreceptor cells far exceeds the number of Cones.
Where in the retina do Cones outnumber Rods?
In the fovea.
Which famous neuroscience researcher pioneered the detection of individual retinal ganglion cell responses to small spots of light on small patches of retina?
Kuffler.
Kuffler developed two classes of retinal ganglion cells, what are they?
On-center and off-center cells.
When do On-center retinal ganglion cells fire?
On-center retinal ganglion cells respond to a spot of light in the receptive field with burst firing of action potentials during entire stimulus.
When do Off-center retinal ganglion cells fire?
For off-center retinal ganglion cells, light stimulus in the central receptive field causes a suppression of firing while light is on, however causes burst of action potentials when light is turned off.
What are the relative proportions of On- to Off-centered cells?
Roughly equal.
How do On- and Off-center retinal ganglion cells contribute to visual perception?
Increased and decreased light levels are detected separately, and can be conveyed to the brain in parallel. The brain can get accurate depictions of the environment by comparing these channels against each other.
A depolarization of retinal bipolar cells leads to an increase or decrease of neurotransmitter release?
Increase.
What was Kuffler's main contribution with respect to Retinal Ganglion Cells?
Retinal ganglion cells do not act as photodetectors, but rather as detectors of the differences between the light levels of the center and surround regions of the retinal receptive field.
How does an On-center Bipolar Cell respond to Cone Stimulus?
Cone to On-Bipolar Cells have sign-inverting synapses. (-)
How does an Off-center Bipolar Cell respond to Cone Stimulus?
Cone to Off-Bipolar Cells have sign-conserving synapses. (+)
How does a Cone Photoreceptor Cell respond to Horizontal cell activity?
The Horizontal Cell to Photoreceptor synapse is sign-inverting. (-)
How does a Retinal Horizontal Cell respond to Photoreceptor cell activity?
The Photoreceptor to Horizontal cell synapse is sign-conserving. (+)
How does a Retinal Ganglion cell respond to Bipolar Cell activity?
The Bipolar cell to Retinal Ganglion cell synapse is sign-conserving. (+)
What do Retinal Horizontal Cells do?
They are thought to have an inhibitory effect on photoreceptor cells.
Describe the "light on center" pathway for an On-Center Retinal Ganglion Cell.
Cone Hyperpolarizes. Cone decreases Neurotransmitter release. On-center Bipolar cell depolarizes. On-center Bipolar cell increases Neurotransmitter Release. On-center Ganglion Fires.
Describe the "light on center" pathway for an Off-Center Retinal Ganglion Cell.
Cone Hyperpolarizes. Cone decreases Neurotransmitter release. Off-center Bipolar cell Hyperpolarizes. Off-center Bipolar cell Decreases Neurotransmitter Release. Off-center Ganglion is supressed.
Light adaptation takes approximately how long?
20 to 30min
The maximum sensitivity to light is at what wavelength region?
500nm
Two reasons for heavy study of the visual system?
Easily accessible and tradition.
There are three types of retinal ganglion cells. Name them for cats and primates.
X (Cat) or P (Primate)
Y (Cats) or M (Primate)
W (Both)
What is the primate analog for the cat X retinal ganglion cells?
P
What is the primate analog for the cat Y retinal ganglion cells?
M
What is the primary visual stream for the X/P retinal ganglion cells?
Ventral Stream Pathway
What is the primary visual stream for the Y/M retinal ganglion cells?
Dorsal Stream Pathway
Give X/P Retinal Ganglion Cell Size, Conduction Velocity, Receptive Field Size?
Medium Size, Medium Speed, and Small Receptive field.
Give Y/M Retinal Ganglion Cell Size, Conduction Velocity, Receptive Field Size?
Large Cells, Fast Speed, and Large Receptive Field.
What is the firing pattern for X/P and Y/M Cells?
X/P have sustained response to stimuli. Y/M have transient response to stimuli (Like RA cells in the somatosensory system)
What is the specialty of the X/P Retinal Ganglion Cells?
High acuity vision, color, and pattern analysis.
What is the specialty of the Y/M Retinal Ganglion Cells?
Good for spatial localization, movement, and perception.
Which layers in the Laterial Geniculate Nucleus of the Thalamus do X/P Retinal Ganglion Cells project to?
Layers 3-6
Which layers in the Laterial Geniculate Nucleus of the Thalamus do Y/M Retinal Ganglion Cells project to?
Layers 1-2
The visual field for a single eye is 150 degrees, how much of that is monocular?
Roughly 30%
What is the rough Visual System pathway to the Visual Cortex (V1 or Striate Cortex)?
Eye to Retina to Optic Nerve to Optic Chiasm to Optic Tract to Lateral Geniculate Nucleus to Visual Cortex (V1:LIV)
There are two main regions of the retina, the Temporal and Nasal regions, at what point do they diverge?
The Optic Chiasm
Information from each eye is kept segregated until which point in the visual system?
After Layer IV in the Primary Visual Cortex.
A lesion in the Right Optic Nerve will cause what visual defect?
There will be a loss of all vision in the right eye.
A lesion at the Optic Chiasm will cause what visual defect?
Tunnel vision: Vision loss from Left Nasal region and the Right Nasal region.
A lesion at the Right Optic Tract will cause what visual defect?
Vision loss from the Nasal Region of Left Retina and Temporal Region of the Right Retina.
A lesion at the Right Visual Cortex will cause what visual defect?
Partial blindness on both sides.
The projections from the fovea are so pronounced that even if you lesion the entire higher region of the visual pathway on one side, it is likely you will have the center of vision. What is this called?
Macular Sparing
Which layers in the LGN are dedicated to the Magnocellular connections?
Layers 1 and 2
Which layers in the LGN are dedicated to the Parvocellular connections?
Layers 3 to 6
The layers in the Lateral Geniculate Nucleus have eye specific organization. Designate each layer with ipsi or cont. Also give cell type.
6 Cont P
5 Ipsi P
4 Cont P
3 Ipsi P
2 Ipsi M
1 Cont M
In the Lateral Geniculate Nucleus of the Thalamus, where do W or K type cells reside?
Intralaminar between the 6 P- and M-type layers.
Give the different names for the primary visual cortex.
Striate Cortex, Visual Cortex, V1, Area 17.
Main projections from the Striate Cortex Layer 2/3.
Association and Callosal Projections.
Main projections from the Striate Cortex Layer 4.
Intracortical Projections.
Main projections from the Striate Cortex Layer 5.
Subcortical Projections.
Main projections from the Striate Cortex Layer 6.
Subcortical Projections to the Thalamus.
Where do Striate Cortex Layer 2/3 pyramidal cells project their axons?
Other cortical areas, for example: Area 18 or Contralateral Area 17.
What is in Layer 1 of the Striate Cortex?
Mainly White Matter.
What is white matter?
Axons, appears white because of myelination.
Layer 4 contains stellate cells that project many axons. Where do they project to?
Other cortical areas within the same region.
Which Sublayer of the Striate Cortex recieves projections from the thalamus?
Layer 4C
Layer 4C-Beta receives projections from which thalamic cell type X/P or Y/M?
X/P
Layer 4C-Alpha receives projections from which thalamic cell type X/P or Y/M?
Y/M
Where do layer 5 large pyramidal cell axons project to?
The Superior Colliculus.
Where do Layer 6 Pyramidal Cell axons project to?
The Lateral Geniculate Nucleus.
Input from the two eyes is kept seperate until converging where in the visual pathway?
Above and Below the Striate Cortex Layer 4
The X/P is a part of the parallel visual pathways. What visual aspects are contained within the X/P pathway?
Visual detail, form, and color.
The Y/M is a part of the parallel visual pathways. What visual aspects are contained within the Y/M pathway?
Spatial location and motion detection.
What are the main cell types of the Striate Cortex?
Stellite Cells: With many axons that project locally.
Pyramidal Cells: With one primary axon that projects outside the cortical region.
What is a ocular dominance column?
Retinal Ganglion Nuclei and the Lateral Geniculate Nuclei preserve information coming from each eye seperately by segregating the activity of each eye. The ocular dominance column is within the striate cortex layer 4 where eye specific connections are made.
What methods can be used to show ocular dominance?
Transneuronal Tracers.
What pathway segregations exist as visual information makes its way into the striate cortex or area 17?
There is ipsilateral or contralateral eye segregation as well as M and P pathway segregation.
Define Retinotopy.
Retinotopy describes the spatial organization of the neuronal responses to visual stimuli. -Wiki
For which regions of the visual pathway is retinotopography maintained?
RGN, LGN, V1 Layer 4C
Describe the Magnification factor with respect to the visual system.
The more receptors that are packed into a specific spatial region of the retina, the more cortex is devoted to that region of the receptive field. As such, changes are much easier to detect and there is a higher degree of detailed information regarding this region.
In the cat area 17 retinotopic map, most of the cortex responds to?
0-20 degrees in elevation and 0-30 degrees asimuthal.
In the cat area 17 retinotopic map, most of the cortex responds to?
0-20 degrees in elevation and 0-30 degrees asimuthal.
What property of Retinal Ganglion Cell receptor fields allows for the detection of edges in the visual field?
Center-Surround (Or On/Off-center) cell functionality.
What is the main visual property detected or encoded by Retinal Ganglion Cells?
Contrast.
Of the X/P and Y/M retinal ganglion cells, which have the center-surround cell functionality?
Both. This allows for true parallel processing.
There are few Lateral Geniculate Nucleus dedicated interneurons. Where are axons from the Lateral Geniculate Nucleus sent?
The Striate Cortex/V1/Area 17
Roughly how many Retinal Ganglion Cell connections does each cell in the Lateral Geniculate Nucleus recieve?
Only a few. Close to 1:1.
The receptor fields of the Lateral Geniculate Nucleus resembles those of which other region?
The Retinal Ganglion Cells and the 4C Layer of the Striate Cortex.
The Lateral Geniculate Nucleus receives afferents from:
Retinal Ganglion Cells as well as some from the Striate Cortex.
Does the cortex project axons to the Retinal Ganglion Cells?
There are no projections fromt he Striate Cortex to the Retinal Ganglion cells.
There is a pattern of change for receptive fields as progress is made through the visual pathway. Explain.
As one progresses from the Retina to the cortex, the receptive fields of these regions increases dramatically.
Complexity of receptive fields increases in higher brain regions. What are Layer 4C cells responsive to in the Striate Cortex?
In general, the cells respond to bars of light with specific orientation. They can also respond to motion.
Describe a Simple Cell in the Layer 4C of the Striate Cortex/Area 17.
Has a receptive field with on/off subregions with specific orientation selectivity. This is the result of many on/off cells lined up.
Describe a Complex Cell in the Layer 4C of the Striate Cortex/Area 17.
Unlike simple cells, Complex cells do not have on/off subregions, but respond to a specific stimuli in a specific orientation in a certain region. Complex cells also detect specific direction of motion.
Who first characterized Simple and Complex cells in the Visual Cortex?
Hubel and Wiesel.
The orderly progression of orientation and direction selectivity is found in which V1 region?
Layer 2/3
Optical imaging of the Striate Cortex allows the visualization of which selectivity patterns?
Ocular dominance and orientation selectivity.
What are the implied functions of the striate cortex/V1?
First, it decomposes the visual would into short line segments of all orientation. Giving Form and Movement Discrimination.

Also, it combines the input from both eyes. As such we get binocular vision and depth perception.
Who proposed the Hypercolumn?
Hubel and Wiesel.
What is a Hypercolumn?
In V1, a hypercolumn is an entire set of columns representing lines of all orientations and input from both eyes for a single region of space.
In a hypercolumn, how are ocular and orientation orientated relative to each other?
They are orthogonal.
What are End Stopped Cells?
End Stopped cells respond to the chape of Bar shaped stimuli that are entirely contained within the receptive field at the correct orientation. If the bar exceeds the receptive field, response is suppressed.
Relative to the previous brain regions ability to process visual information, what is significant about the Area V2?
They have the ability to extract more abstract information about the visual field, and resopond to illusory contours. Looks for the perceptive contour.
What visual properties make the Dorsal Visual Stream Pathway important?
Motion Detection and Direction Selectivity.
What visual properties make the Ventral Visual Stream Pathway important?
Determining form and shape, extracting visual details, pattern recognition, and color vision.
What is the primary Retinal Ganglion/Lateral Geniculate Nucleus cell for the Dorsal Visual Stream Pathway?
Y/M-type and Magnocellular.
What is the primary Retinal Ganglion/Lateral Geniculate Nucleus cell for the Ventral Visual Stream Pathway?
X/P-type and Parvocellular.
Direction selectivity occurs in which region first before traveling to Middle Temporal Area (Area MT)?
Layer 2/3 of the V1 cortex.
What visual properties make the Area MT important for the Dorsal Visual Stream Pathway?
Has large receptive fields and direction selective columns.
What is the Aperture Problem?
Given the limited size of a receptive field, it is difficult for neurons to interpret the information they see, often causing them to interpret a part of a pattern rather than the pattern as a whole.
The aperture problem helps define what problem with the visual system?
Helps determine how neurons are interpreting the information they are receiving and gives us an idea about the hierarchy of the system.
How do V1 striate cortex and the area MT differ in their response to the aperture problem?
V1 responds only to the components of the pattern. The Area MT has a small portion of cells that respond to the pattern as a whole. These are called Pattern Direction-Selective Neurons.
Pattern Direction-Selective Neurons need input from which brain regions in the visual system?
V1 and area MT neurons.
What does damage of the Middle Temporal Area cause?
Saccadic and smooth pursuit defects. No motor defects.
If visual information is passed from the V1 to V2 to the Inferotemporal Cortex, which visual stream is it in?
The Ventral Visual Stream Pathway.
Where does the retinotopic map representation of space break down?
Afte the 4C layer of the striate cortex.
The inferotemporal cortex is sensitive to what stimuli?
Shape and color.
Face cells are an example of what property of the Inferotemporal cortex?
Complex shape specific receptive fields.
The Sheinberg experiment found that IT neurons respond to what?
Isolated objects as well as objects in complicated images, but only when aligned to the fovea.
What experiment were Hecht, Schlaer, and Pirenne known for in the visual system?
They determined what the dimmest light flash was that could be detected by the human retina.
Hecht, Schlaer, and Pirenne determined that which considerations were very important for their experiment to show the dimmest light flash detectable by human?
The state of the subject: Dark adjusted for 30min

Location of stimulus: Highest abundance of Rods at 20deg off fovea

Size of stimulus: 20min in diameter

Duration of Stim: 100ms

Color of Stimulus: 510nm
The response of a photoreceptor to light can be mapped on a logarithmic scale. What does it look like?
S-function.
Hecht, Schlaer, and Pirenne determined that you could get a response from less than how many photons?
30 photons.
Baylor, Nunn, and Schnaft found rods show response to variable number of photon isomerizations. This indicated what?
That Rod Photoreceptors respond to single photon events.
Even in absolute darkness humans can perceive light. What is this called, and what causes it?
It is called Dark Light. Dark light is caused by thermal isomerizations, or random isomerization events.
Metabotropic glutamate receptors mediate what type of cell response in the visual system?
On-bipolar cells or Depolarizing Bipolar Cells.
Depolarizing or On-Bipolar cells in the Visual system utilize what receptor?
mGluR6
mGluR6 is continually active in On-Bipolar cells of the visual system under what conditions?
When it is dark.
Hyperpolarizing or Off- Bipolar cells utilize what receptor?
ionotropic glutamate receptors.
Retinal Ganglion cells project to what three regions of the brain?
90% Lateral Geniculate Nucleus
10% The Superior Colliculus
Undetermined amount to Suprachiasmatic Nucleus.