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59 Cards in this Set

  • Front
  • Back
What is the retinofugal projection?
The neural pathway that leaves the eye, beginning with the optic nerve.
What are the three basic components of the optic nerve?
The optic nerve, the optic chiasm, and the optic tract
Where does the optic nerve exit the eye?
At the optic disk
What is decussation?
The crossing of a fiber bundle from one side of the brain to the other, (which happens at the optic chiasm with the axons originating in the nasal retinas crossing from one side to the other)
What are the three possible destinations of axons in the optic tract?
1. Hypothalamus
2. Midbrain
3. LGN (laternal geniculate nucleus) in the dorsal thalamus - neurons in the GN give rise to axons that project to the primary visual cortex (called optic radiation)
What is optic radiation?
The projection of axons from the LGN to the primary visual cortex
For axons that go from the optic tract to the midbrain, what are two possible destinations?
The pretectum (which controls the size of htep upil and certian types of eye movement)
2. Superior colliculus, called the optic tectum in nonmammalian vertebrates (major target of retinofugal projection for them)
What is retinotectal projection?
Projection from the retina to the super colliculus
What is the superior colliculus involved in?
Orienting the eyes in response to new stimuli in the visual periphery.
How many LGN are there?
Two; one for each optic tract
What layer of the LGN is most ventral?
Layer 1
What happens to the visual field if the optic nerve on the left side is cut?
Vision will be lost completely in the left eye
What happens to the visual field if the optic tract on the left side is cut?
The right visual field will be lost
What happens to the visual field if the optic chasm is cut?
Some visual field from both sides will be cut.
What is LGN the gateway to?
The visual cortex
What ganglion from the retina switch at the optic chiam and which switch?
Temporal stay on the same side; nasal switch
Describe the size differences in the different parts of the LGN?
Layer 3-6 are smaller, so thse dorsal layers are called parvocellular LGN and the ventral layers are called magnocellular LGN
What exists in addition to the six principle layers of the LGN?
Konicellular layers, which receive input frmo the nonM-nonP types of retinal ganglion cells
What layer integrate information from the nasal retina and which from teh temporal?
Nasal: 1, 4, & 6
Temporal: 2, 3, & 5
Describe the receptive fields of the diffferent layers?
Magnocellular LGN layers (the ventral ones) have relatively large center-surround receptive fields, etc.; insensitive to differences in wavelength
Describe the receptive field of parveocllular LGn ccels?
Like P-tyep retinal ganglion cells, they have relatively small center-surround receptive fields and respond to stimulation of their receptive field centers with a sustained increase of action potentials ; many exhibit color componency
Describe the receptive field of cell in the koniocellular layers?
Center-surrounds and ahve either light/dark or color opponency
How are ON and OFF cells distributed in layers of the LGN?
ON and OFF center cells are intermixed
What is the major source of input to the LGN?
The primary visual cortex (not the retina); also receives input from retina and brainstem
Does input to the LGN from the brainstem evoke action potentials?
No, but it can powerfull modulate the magnitude of LGN responses to visual stimuli
Where is the primary visual cortex/
Brodmann's area 17, lcoated in the occipital lobe surrounding the calcarine fissues
What are two other temrs for the primary visual cortex?
V1 and striate-cortex
Where is retinotropy?
An organization whereby neighboring cells int eh retina feed information to neighboring places in their taget structure-in this case, the LGN and straite cortex ~ two-dimensional surface of hte retina is mapped onto the two-dimension surface of subsequent structures
Why is the mapping of the visual field onto a retinotopically organized structure often distorted?
Visual space is not sampled uniformly in the retina; there are more ganglion cells with receptive field in or near the fovea, so the central few degrees of the visual field are overrepresented in the retinotopic map
If a person is seen as 1-9, and the left eye sees 8-1 while the right eye sees 9-2, how is this image represented on the striate cortex?
5-9 on the left (inverted) and 1-5 on the right (inverted); pg. 320
Describe the cytoarchitecture of the striate cortex?
White matter --- VI, V, IVCbeta, IVCalpha, IVB, IVA, III, II, I ---- pia
How thick is the striate cortex from white matter to pia?
About 2 mm
Where are spiny stellate cells predominantly found?
In the two tiers of layer IVC
Where are the pyramidal cells found?
Outside layer IVC; only pyramidal cells send axons out of striate cortex
Where do the majority of axons from the LGN terminate in the striate cortex?
Layer IVC
Where are magnocellular LGn and parvocellular LGN neurons respectively projected?
To layers IVCalpha and IVCbeta, respectively; therefore, IVC contains two overlapping retinotopic maps (one from the magnocellular LGN) and the other from the parvocellular LGN; koniocellcular LGNxons
Where koniocellular LGN axons synapse?
In layers II and III
How is the location of radioactive axon terminals visualized?
Autoradiography: FIrst by placing a film of emulsion over thin sections of striate cortex and later developing the emulsion like a photograph the resulting collection of silver grains on the film marked the location of the radioactive LGN inputs
Describe ocular dominance columns
The left eye and right eye inputs to layer IV are laid out as a series of alternating bands
Describe intracortical connections.
Maintain the retinotopic organization established in layer IV; however, the axons of some ayer III pyramidal cells extend collateral branches that make horizontal connections within layer III
Where is the first time information from the left and right eye mix.
When layer IVC stellate cells project axons radially up mainly to layers IVB and III where, for the first time, information from the left eye and right eye begins to mix; whereas all layer IVC neurons receive only monocular input most neurons in layers II and III receive binocular input coming from both eyes
Where do layer V of the striate cortex pyramidal cells send their axons?
All the way down to the superior colliculus and pons
Where do cytochromic oxidase blobs originated?
On an ocular dominance stripe in layer IV.
What are IVCalpha neurons insensitive to?
Wavelength
What are IVbeta neurons sensitive to?
Exhibit center-surround color opponency
What layers of the striate cortex are binocular?
Those superficial to IVC
WHat is the a shape of the receptive fields in the retina, LGN, and layer IVC?
Circular; give their greatest response to a spot of light matched in size to the receptive field center
What is the shape of the receptive field of many neurosn in VI?
An elongated bar of light ; the greatest response is given to a bar with a particular orientation; penpendicular bars generally elicit much weakers responses
Describe an orientation column.
All of the orientation selective neurons maintained the orientation they were selective trom layer VI to layer II
What happens to orientation sleectivity as one progresses tangentially through a layer?
rientation shifts
WHat are orientatoin-selective neurons specialized for?
Analysis of object shape
Describe directional selectivity.
Respond when a bar of light at the optimal orientatoin moves perpendicular to the orientation in one direction, but not in the opposite direction; subset of the cells that are orientation selective; receive input form the manocellular layers of the GN
What does it mean that neuron in the LGN have antagonistic center-surround receptive fields?
A small spot int eh center of the receptive field may yield a much stronger response than a larger spot also covering the antagonistic surround
What are simple cells?
Have a receptive field elongated along an axis, similar to the concentric receptive fields of retinal and LGN cells
What are compelx cells?
Orientation selective neurons in VI that do not have distinct ON and OFF regions
Describe the receptive field of most blob neurons.
Mostly circular; some have the color-opponent center-surround organization observed in the parvocellular and koniocellular layers of hte lGN; others have red-gree or blue-ellow color opponency with no surround regions at all
What are the three parallel pathways reaching the primary visual cortex.
Magnocellular pathways: M-type anglion cells in retina to magnocellular in LGN to layers IValhpa and Layer IVB in VA
Blob pathway: nonM-nonP ganglion cells in retina to koniocellular cells in LGN to blob in V1
Parvo-interblob pathway: P-trype ganglion cells in the retina to parvocellular cells in the LGN to layers IVCbeta and interblob cells in V1
Layers IVC can cross over to blob in V1
What are the three parallel pathways reaching into the primary visual cortex respectively responsible for?
Manocellular pathway (motino), blob pathway (color), and parvo-interblob pathway (shape)
WHat is a cortical module?
A 2 by 2 mm chunk of striate cortex that is both necessary and sufficient to analyze the image of a point in space; necessary because its removal would leave a blind spot for this point in the visual field; sufficient because it contains all the neural machinery required to analyze the participation of this point in oriented and/or colored contours