Lecture 7: Visual Pathways & Eye Movements Flashcards
(50 cards)
What are visual fields?
Area that a person is able to see when both eyes are fixed in one position
What is a retinal field?
When light passes from objects in the visual fields, through the pupil to subtend an image upon the retina its creating a retinal field
What type (direction) of image does a visual field project onto the retinal field?
Inverted and reversed
An object of attention is focuesed and centered at what location on the retina?
Fovea centralis and macula lutea
Medial to the macula of the eye is the _______________, region where retinal axons leave the eye as the optic nerve
Optic disc
**Photoreceptors are absent from this region, which creates our blind spot
Visual fields are subdivided into what 2 zones?
Binocular zone: broad central region seen by both eyes
Monocular zones (R/L): seen only by the corresponding eye
Example of retinal fields: the left half of the visual field forms an image upon the nasal half of the ________ retina and the temporal half of the _________ retina
Left; right
Example of retinal fields: The right half of the visual field forms an image upon the nasal half of the ________ retina and the temporal half of the ________ retina
Right; left
Two optic nerves partially decussate in the optic chiasm. The nasal half of each retinal to the ______________ optic tract and the temporal half of each retina to the _____________ optic tract
Contralateral; ipsilateral
What fibers is the optic tract composed of?
Fibers from the temporal retina of the ipsilateral eye and fibers from the nasal retina of the contralateral eye
**this allows for depth perception in our vision*
After the optic nerve decussates, it is considered the optic tract. Where does the optic tract go from here and where does it terminate?
Curves posteriorly around the cerebral peduncle and terminates in the lateral geniculate nucleus (LGN)
What is the ventral base versus the dorsal and lateral borders of the lateral geniculate nucleus (GN) formed by?
Ventral base = incoming optic tract fibers
Dorsal and lateral borders = optic radiations
What are the 2 cell layers of the lateral geniculate nucleus and what inputs do each receive?
Magnocelluar layer (contains large cells): receives ganglion cell inputs relayed from rods -> larger receptive fields and thick, rapidly conduction axons, sensitive to moving stimuli
Parvocellular layer (contain small cells): receive ganglion cell inputs relayed from cones -> small receptive fields, slower conducting axons, tonically responsive to stationary stimuli
How many layers does the LGN have?
6
Layers 1, 4 and 6 of one LGN correspond to the nasal region of the opposite eye
Layers 2, 3, 5 of one LGN correspond to the temporal region of the same eye
Secondary neurons from the LGN extend a large bundle of myelinated fibers called what?
Optic radiation
What is the function of optic radiations?
Relay information to the primary visual cortex (striate cortex) located on the upper and lower banks of the calcarine sulcus
**Optic radiations are the secondary neurons of the visual pathway
Optic radiations are divided: fibers from the lower quadrant of the contralateral hemifields originate from the _______________ portion of the LGN, arch caudally to pass through the retrolenticuar limb of the internal capsule and target the ____________ bank of the calcarine sulcus on the _______________
Dorsomedial portion of LGN; superior bank of calcarine sulcus: on the cuneus
Optic radiations are divided: fibers from he upper quadrant of the contralateral hemifields originate from the _______________ portion of the LGN, arch rostrally, passing into the white mater of the temporal lobe to form a broad U-turn, the ______________, and target the _________ bank of the calcarine sulcus, on the ______________
Ventrolateral portion of the LGN; the Meyer loop; inferior bank of the calcarine sulcus; on the lingual gyrus
Optic radiations are divided: fibers conveying information from the macula and fovea originate from _____________ regions of the LGN and pass to _________ portions of the visual cortex
Central regions of the LGN; caudal portions of the visual cortex
Why is the Meyers loop that is made by optic radiation fibers from the upper quadrant clinically significant?
Because the loop actually loops down into the temporal lobe so temporal lobe damage can potentially produce a superior visual field deficit
Visual pathway ends retinotopically in the cortex above and below the _____________ sulcus. INferior visual fields project to the cortex ________ (above/below) the sulcus, superior fields project to the cortex ___________(above/below) the sulcus and the macula is represented more posteriorly and peripheral fields more anteriorly
Calcarine sulcus; Inferior field = above; superior field = below
What brodmann’s area is the primary visual cortex/striate cortex?
17
The primary visual cortex/striate cortex is surrounded by brodmann’s areas ______ and _____. These areas and related parts of the temporal and parietal lobes are grouped as the ___________________ cortex
18 & 19; visual association cortex (extrastriate cortex) -> parieto-occipito-temporal area
The superior colliculus spatiallly directs what reflexes?
Head movements and visual reflexes
