Vision Tracts Flashcards
(45 cards)
How are visual system lesions described?
In terms of their visual field deficits
What happens to an image on the retina?
Inverted both laterally and vertically
How do the two optic nerves decussate?
The nasal half of each retina goes to the contralateral optic tract.
The temporal half of each retina goes to the ipsilateral optic tract.
What is the optic tract made up of?
Fibers from temporal retina (ipsilaterally) and nasal retina (contralaterally)
What is the tract for vision (up to brain)?
Optic nerve – Optic chiasm – Optic tract (through cerebral peduncle) – lateral geniculate nucleus
What is the ventral base of LGN made up of?
Incoming optic tract (retinogeniculate) fibers
What is the dorsal border of LGN made up of?
Outgoing optic radiations
Magnocellular layers
- From layers 1,2
- Ganglion cell inputs from rods – larger RFs (thick/rapidly conducting axons)
- Sensitive to moving stimuli
Parvocellular layers
- Layers 3-6
- Ganglion cells inputs from cones – small RF (slow conducting axons)
- Stationary stimuli
- High-acuity color vision
Where do ganglion cells from the temporal retina terminate?
- Travel uncrossed and terminate @ layers 2,3,5 of ipsilateral LGN
- Temporal VFs
Where do ganglion cells from the nasal retina terminate?
- Cross and terminate @ layers 1,4,6 of contralateral LGN
- Nasal VFs
Describe right visual field tracts
Nasal retina (R) goes to layers 1,4,6 of Left LGN Temporal retina (R) goes to layers 2,3,5 of R LGN
How is each point represented 6 times?
Optic tract axons branch into multiple layers even though they’re from the same vision field
Where do fibers from the lower quadrant of CL hemifield go?
- Originate from dorsomedial portion of LGN
- Pass through retrolenticular limb of int. capsule
- Terminate @ superior bank of calcarine sulcus (cuneus)
Where do fibers from the upper quadrant of CL hemifield go?
- Originate from ventrolateral portion of LGN
- Arch rostrally, going into white matter of temporal lobe and forming Meyer loop
- Terminate @ inferior bank of calcarine sulcus (lingual gyrus)
Where do fibers from the macula and fovea go?
- Originate from central regions of LGN and pass caudally on the visual cortex
What would a lesion to the temporal lobe cause?
Superior visual field deficit @ Meyer’s loop
Representation of macula in visual cortex?
- Disproportionately large and posteriorly (@ the occipital pole)
What is responsible for depth perception?
Combination of images from both eyes
What “area” is the calcarine sulcus?
Broadmann area 17
What areas correspond with the visual association cortex?
Broadmann areas 18 and 19
(temporal and parietal lobes)
*parieto-occipito-temporal areas
Role of superior colliculus in vision?
- Spatially directs head movements and visual reflexes
- Fibers pass over the medial geniculate nucleus in the brachium of superior colliculus and terminate in sup. colliculus
- Directs eye movements
Role of pretectum area in vision?
- Bilateral group of nuclei near midbrain/forebrain jxn
- Respond to pretectal nuclei respond to varying intensities of illuminance
- Pupillary light reflex
Innervation for pupillary dilator m.
Sympathetic postganglionic fibers (from superior cervical ganglion)
