2. Topography 1 Flashcards
Why is an organization important in the visual pathway?
To maintain maps of the visual world. Such that the image formed on the retina is maintained in a parallel manner.
In the sensory/ motor cortex unequal distribution is seen - some aspects cover a larger area in the cortex why?
Distribution relates to the number of receptors (Sensory or motor) found in that are, some areas require more space due to this.
Reason for over representation of the fovea in the cortex?
A lot of ganglion cells are carrying info to the cortex in comparison to the peripheral retina.
THIS IS KNOWN AS THE MAGNIFICATION FACTOR.
Describe the organization of cells that are together in point in space, in relation to the cortex and RGCs.
2 points together in space = next to each other in the retina & fibers from those ganglion cells stay together.
What is monocular correspondence?
In 1 eye the adjacent information remains adjacent as you move to the visual maps.
2 types of point-to-point correspondence?
Monocular & Binocular
Binocularity in LGN?
No binocularity in LGN
Describe the overlap seen when eyes look straight ahead vs when eyes converge?
Straight ahead: Visual fields overlap
Eyes converge: Bigger overlap of visual fields
Describe the overlap seen when eyes look straight ahead vs when eyes converge?
Straight ahead: Visual fields overlap
Eyes converge: Bigger overlap of visual fields
Are eyes the only determining factor of visual fields?
No- head and body movements also contribute to movement of field view.
How does info from photoreceptors, horizontal, amacrine and bipolar cells move to optic nerve ?
Info from all this 4 cells moves to retinal ganglion cell layer, that gives rise to a single axon that moves to the optic disc, this will exit through optic nerve head and move to chiasma.
very few fibers in the fovea, why?
Because very little overlying tissue in the fovea
RGCs in the fovea location?
Found at the periphery, because it has been pushed aside
Horizontal Raphe denotes?
Horizontal meridian of the eye
Describe the fibers that are above and below the raphe?
The fibers arcuate as they move to the optic disc
Is raphe observed at the optic disc, if yes- explain?
Yes
All fibers that emerge below the raphe move to the lower portion of the disc
A distinction/ separation is observed of fibres coming from the temporal vs nasal retina- TRUE OR FALSE?
TRUE
What is arcuate fiber trajectory?
Virtually no crossing between upper and lower at the level of Raphe.
Raphe more distinct for nasal or temporal region?
More distinct for nasal region
What is extra striated cortex?
Areas beyond V1
Nasal fields crossing leads to?
Representation of hemi-fields
Why is rotation of retinal coordinate maps important?
To allow it to get plugged into LGN.
Describe what happens to nasal fibers- Inferior peripheral and superior peripheral at the chiasma and why?
Inferior peripheral: Anterior knee of Willbrand
Superior peripheral: Posterior knee of Willbrand
WHY- Fibers are trying to keep a map a cross the chiasma
Macular crossing occurs at what end of the chiasma?
Posterior end
Eye is distal to the brain- meaning?
Eye is near to the brain
In the distal optic nerve- Macular fibers take up central position, why?
A lot more fibers are emmerging from the macular compared to the periphery
Direction of rotation of retinal coordinates at the chiasma?
Implication of this?
Nasal
Implication: Puts upper retina medially & lower retina put laterally
Once map emerges from optic tract UT/UN replaced by?
Superior
Nasal and Temporal fibers go to which layers:
Nasal: 1,4 & 6
Temporal: 2,3 & 5
In the cortex, Raphe corresponds to?
Sulcus
How many individual maps within the LGN?
12
What part of the maps do not overlap with each other?
Monocular crescents do not overlap
