Visual Pathways and Eye Movements Flashcards
Visual stimuli are ultimately relayed to the primary visual cortex via the thalamus.
The primary visual cortex is aka the _____ cortex, located on the upper and lower banks of the _____ sulcus, which is Brodmanns area _____
Striate; calcarine; 17
The visual pathway ends in the primary visual cortex retinotopically. What does this mean for inferior vs. superior visual fields?
Inferior visual fields project above calcarine sulcus
Superior visual fields project below calcarine sulcus
The visual association cortex is known as the extrastriate cortex, composed of brodmanns areas ____ and _____ which surround the striate cortex and comprise the rest of the ______ lobe, as well as related parts of the temporal and parietal lobes. It is heavily interconnected with brodmanns area 17.
18; 19; occipital
The _____ nucleus also sends targets to the visual association cortex which helps interpret location, motion, form, and color
Lateral geniculate
What are 2 visual cortices besides the striate and extrastriate?
Superior colliculus
Pretectal/pretectum area
Function of superior colliculus as visual cortex
Spatially directs head movements and visual reflexes
2 sources of input to superior colliculus as visual cortex
Retinal input = select fibers from each optic tract bypass the LGN, passing over the medial geniculate nucleus and terminating retinotopically in superior colliculus
Cortical input = cells in Brodmann 17 project to superior colliculus in retinotopic pattern
[also receives some spinotectal/somatosensory and auditory inputs]
The prectectum area is a bilateral group of interconnected nuclei located near the midbrain-forebrain junction. What are the 3 input sources for the pretectum as a visual cortex?
Afferent bilateral fibers from the optic tract
LGN and suprachiasmatic nucleus
Function of pretectum area as a visual cortex
Pretectal nuclei respond to varying intensities of illuminance, mediating non-conscious behavioral responses to acute changes in light
Area that you see when both eyes are fixed in one position
Visual field
Within the visual field, the object of attention is focused and centered at the location of ____ and ____
Fovea centralis
Macula lutea
The macula lutea is lateral to the ____ ___ which is the region where the retinal axons leave the eye as the optic nerve, and the area where photoreceptors are absent (blind spot)
Optic disk
The macula is represented more _______ in the brain, in the region of the occipital pole, while peripheral visual fields are represented more ______
Posteriorly; anteriorly
Visual field is subdivided into what 2 zones?
Binocular zone = broad central region seen by both eyes
Monocular zones (R/L) = seen only by corresponding eye
Location on the retina that an object in the visual field is projected
Retinal field
Divisions of the retinal field
Nasal half (upper quadrant + lower quadrant)
Temporal half (upper quadrant + lower quadrant)
Image formed on the retina is inverted in both ____ and _____ dimensions
Lateral; vertical
The image formed on the retina is inverted in both lateral and vertical dimensions
For example:
The left half of the visual field forms an image upon the ______ half of the left retina and the _____ half of the right retina
Nasal (right); temporal (right)
The 2 optic nerves partially decussate in the optic chiasm. The ___ half of each retina projects to the contralateral optic tract. The ____ half of each retina projects to the ipsilateral optic tract
Nasal; temporal
What is the functional purpose of the decussation of the optic nerve?
Depth perception
____ ____ = fibers from temporal retina (ipsilateral eye) + fibers from nasal retina (contralateral eye)
Optic tract
The optic tract curves posteriorly around the _____ _____ to terminate in the ______ ____ nucleus
Cerebral peduncle; lateral geniculate
The lateral geniculate nucleus consists of six layers of ______ fibers which terminate in a precise retinotopic pattern.
The ventral base is formed by incoming optic tract (retinogeniculate) fibers, while the dorsal and lateral borders are formed by the outgoing _____ _____
Myelinated
Optic radiations
The lateral geniculate nucleus is subdivided into what 2 layers based on anatomical origin and functional type?
Magnocellular layer = layers 1 and 2 (ventral)
Parvocellular layer = layers 3-6 (dorsal)
Describe the magnocellular layer in terms of cell size and source of input
Contains large cells
Receives ganglion cell inputs relaying from rods — larger receptive fields and thick, rapidly conducting axons, sensitive to moving stimuli
Describe the parvocellular layer in terms of cell size and source of input
Contains small cells
Receives ganglion cell inputs relaying from cones — small receptive fields, slower conducting axons, tonically responsive to stationary stimuli, high acuity color vision
T/F: Within the 6 layers of the lateral geniculate nucleus, the pattern is the same in each layer. A given point in the visual field is represented by a column of cells extending through all 6 layers
True
Note crossed vs. uncrossed, what layers, and ipsilateral vs. contralateral:
Ganglion cell axons that arise in the temporal retina are ________ and terminate in layers _____, ____ and _____ of the __________ LGN
Uncrossed; 2, 3, 5; ipsilateral
Note crossed vs. uncrossed, what layers, and ipsilateral vs. contralateral:
Ganglion cell axons that arise in the nasal retina are ________ and terminate in layers _____, ____ and _____ of the __________ LGN
Crossed; 1, 4, 6; contralateral
The right visual field consists of the nasal retina of the right eye and temporal retina of the left eye.
The right nasal retina projects to layers ____, _____, and _____ of the ______ LGN.
The left temporal retina projects to layers _____, _____, and ____ of the _____ LGN.
1, 4, 6; left
2, 3, 5; left
The same point in visual space is represented ____ times — once in each layer of the LGN, located in the same medial-lateral position. Layers also run rostral—> caudal, representing __________ axis
Six; inferior-superior
[note that optic tract axons branch in multiple layers even though they arise from the same visual field
What are optic radiations?
Large bundle of myelinated fibers extended from secondary neurons of LGN
Maintain retinotopic organization, but individual fibers carry info from one eye
Optic radiations relay to the ______ cortex
Primary visual (striate)
Divisions of optic radiations
Fibers from lower quadrant of contralateral hemifields
Fibers from upper quadrant of contralateral hemifields
Fibers conveying info from macula and fovea
One division of optic radiations: fibers from the lower quadrant of the contralateral hemifields, originates from ______ portion of LGN and arches caudally to pass through the ______ limb of the internal capsule
These fibers target the superior bank of the ______ sulcus, on the ______
Dorsomedial; retrolenticular
Calcarine; cuneus
One division of optic radiations, the fibers from the upper quadrant of the contralateral hemifields, originate from the _______ portion of the LGN. They do not pass directly caudal to the visual cortex, but arch rostrally, passing into the white matter of the ______ lobe to form a broad U-turn called the _____ ____
Ventrolateral; temporal; Meyer’s loop
One division of optic radiations, the fibers from the upper quadrant of the contralateral hemifields, originate from the ventrolateral portion of the LGN. They do not pass directly caudal to the visual cortex, but arch rostrally, passing into the white matter of the temporal lobe to form a broad U-turn called the Meyer’s loop.
What happens with temporal lobe damage considering this association?
Temporal lobe damage can produce a superior visual field deficit via Meyer’s loop
One division of optic radiations, the fibers from the upper quadrant of the contralateral hemifields, originate from the ventrolateral portion of the LGN. They do not pass directly caudal to the visual cortex, but arch rostrally, passing into the white matter of the temporal lobe to form a broad U-turn called the Meyer’s loop.
These fibers target the inferior bank of the calcarine sulcus, on the _____ _____
Lingual gyrus
One division of optic radiations, the fibers conveying info from the macula and fovea, originate from ______ regions of the LGN and pass to the caudal portion of the visual cortex
Central
Voluntary eye movements are controlled by ______ eye fields (area ______) in the posterior portion of the middle frontal gyrus
Corticotectal fibers descend to the ______ _____ which will control the ______ of CN III, IV, and VI
Frontal; 8
Superior colliculus; LMN
Involuntary eye movements involve the _______ eye fields in the visual association cortex projecting _________ fibers to the superior colliculus — may be associated with following a target
Occipital; corticotectal
Lesion of the visual system characterized by blindness in 1/2 of the visual field
Hemianopia
Lesion of the visual system characterized by blindness of a quadrant of the visual field
Quadrantanopia
Conditions in which visual field losses are similar in both eyes
Homonymous visual fields
Conditions in which the two eyes have non-overlapping field losses
Heteronymous visual fields
Visual field loss of one eye can be superimposed on that of other eye (symmetrical)
Congruous
The closer a lesion is to the visual cortex, the more ______ it is likely to be
Congruous (visual field loss of one eye can be superimposed on that of other eye)
The more ______ a lesion is in the optic tract or radiations, the more likely it is that it will be incongruous
Anterior
Damage anterior to optic chiasm affects which eye(s)?
Only ipsilateral eye
Damage at the optic chiasm causes ________ visual deficits
Heteronymous (the two eyes have non-overlapping field losses)
Damage behind the optic chiasm causes _____ deficits
Homonymous (visual field loss similar in both eyes)
Condition in which destruction of one optic n. causes blindness in the eye that it arises
Monocuar blindness
Condition in which damage to one side of the optic chiasm destrooys noncrossing ipsilateral fibers (arising in temporal retina)
Nasal hemianopia (blindness in nasal half of visual field)
Condition arising from damage to the crossing fibers from both eyes at the optic chiasm
Bitemporal hemianopia (one type of heteronymous hemianopia — the two eyes have non-overlapping field losses)
Condition caused by destruction of one optic tract
Contralateral homonymous hemianopia
Describe the effects of contralateral homonymous superior quadrantopia
Damage to one temporal lobe and/or parts of optic radiation
Specific to the contralateral superior quadrant of each visual field
[Can also see homonymous inferior quadrantopia]
Contralateral homonymous hemianopia is due to damage to one ______ lobe. However, since _____ representation is very large there is _______-sparing
Occipital; macular; macular
Condition caused by infarction of the left occipital lobe and posterior corpus callosum, typically secondarily due to occlusion of the posterior cerebral artery
Associative visual agnosia
What effect does associative visual agnosia have on a patient?
It disconnects the language area from the visual association cortex, so patient cannot name or describe an object in the visual field but can recognize and demonstrate its use
[thus visual perception is intact]
Patients may also be alexic and writing ability may be affected
