neuro 3-18 -- visual system (clinical syndromes start on card 63)
Visual agnosia
-- "beyond" V1; are cognitively unaware of certain aspects of visual information in visual field -- Damage to higher visual pathways (dorsal and ventral stream) -- Not blindness, but agnosia ("lack of knowledge") -- Posterior parietal lesion → hemineglect
Bitemporal hemianopsia
-- A lesion to medial aspect of optic chiasm that damages decussating fibers from each nasal hemiretina -- Loss of lateral visual hemi‐field for both eyes
Presbyopia
-- Age‐related impairment -- Lens hardens, becomes less compliant -- Results in inability to focus on near objects (why many older folks need reading glasses)
why do we have a "blind spot" on the retina
-- Because optic disk contains no photoreceptors, this region of retina is insensitive to light -- This corresponds to blind spot of retina -- Both eyes have a blind spot; they do not overlap in visual field -- You don't usually notice blind spots because brain cognitively "fills in" these areas of visual field
Age‐related macular degeneration
-- Increases in prevalence in sixth decade -- Leading cause of blindness in the elderly -- Loss of central vision and acuity
Optic Neuritis
-- Inflammatory demyelinating disorder often related to multiple sclerosis -- Symptoms of eye pain, decreased acuity, and impaired color vision -- Recovery is common
Macular sparing
-- Vascular lesions of occipital lobe -- Both MCA and PCA supply blood to V1 cortical area representing the fovea
Prosopagnosia
-- face blindness -- Bilateral damage to occipitotemporal cortex (ventral streams) -- inf occipital‐temporal area = color, face, letter and number recognition areas -- fusiform face area = face recognition
The _______________ is the site where optic nerve exits the eye; it is ________________ to the fovea.
-- optic disk -- medial (nasal) to the fovea
which of the following does NOT belong: A. Brodmann area 22 B. primary visual cortex C. V1 D. striate cortex
A -- Brodmann area *17*
A lesion of the R optic nerve would lead to: A. Right (ipsilateral) monocular blindness B. Bitemporal heteronymous hemianopsia C. Left (contralateral) homonymous hemianopsia D. Left superior (contralateral) quadrantanopia E. Left (contralateral) homonymous hemianopsia with macular sparing
A -- Right (ipsilateral) monocular blindness https://www.youtube.com/watch?v=cG5ZuK0_qtc
the primary visual cortex stems from which of the following: A. lateral geniculate nucleus B. superior colliculus C. pretectal area D. suprachiasmatic nucleus
A -- lateral geniculate nucleus (is the area of major sensory input from retina)
A pt with MS presents in the clinic with eye pain, decreased acuity, and impaired color vision. They are likely suffering from: A. Papilledema B. Optic neuritis C. Macular degeneration D. Presbyopia
B -- Optic neuritis note: recovery is common
which of the following is NOT true of Type M ganglion cells: A. low acuity B. color-sensitive C. high sensitivity D. movement‐sensitive
B -- color-sensitive = *type-P ganglion cells*
which of the following does NOT belong: A. light B. photoreceptor depolarization C. decreased cGMP concentration D. Na+ channels closed
B -- photoreceptor *hyperpolarization* note: "Dark Depolarizes"
which of the following corresponds to "Orientation; visually guided movements of eyes": A. lateral geniculate nucleus B. superior colliculus C. pretectal area D. suprachiasmatic nucleus
B -- superior colliculus
A pituitary tumor would lead to: A. Right (ipsilateral) monocular blindness B. Bitemporal heteronymous hemianopsia C. Left (contralateral) homonymous hemianopsia D. Left superior (contralateral) quadrantanopia E. Left (contralateral) homonymous hemianopsia with macular sparing
B. Bitemporal heteronymous hemianopsia note: pituitary tumor = lesion of decussating fibers in optic chiasm https://www.youtube.com/watch?v=cG5ZuK0_qtc
which of the following does NOT relate to the ventral (P) pathway: A. what is the object B. what is the objects color C. where is the object D. what is the shape of the object
C -- "where is the object" = dorsal (M) pathway, low visual acuity note: P pathway focuses on finer details, high acuity
which of the following is NOT true of Type M ganglion cells: A. Cones and rods B. In periphery of retina C. Small dendritic fields D. Low acuity, high sensitivity, movement‐sensitive
C -- *Large ("magno")* dendritic fields note: "type M = magno = LARGE dendritic fields"
which of the following is NOT true of the photopic cone system: A. works at higher levels of illumination B. color vision C. low resolution D. high acuity E. "day vision"
C -- *high* resolution
A 67 y/o pt presents in the clinic with loss of central vision and acuity. They are likely suffering from: A. Papilledema B. Optic neuritis C. Age-related macular degeneration D. Presbyopia
C -- Age-related macular degeneration
Lesion of the right optic tract would lead to: A. Right (ipsilateral) monocular blindness B. Bitemporal heteronymous hemianopsia C. Left (contralateral) homonymous hemianopsia D. Left superior (contralateral) quadrantanopia E. Left (contralateral) homonymous hemianopsia with macular sparing
C -- Left (contralateral) homonymous hemianopsia *note*: can occur with lesions of the right optic tract, right LGN or right optic radiation https://www.youtube.com/watch?v=cG5ZuK0_qtc
which of the following does NOT belong: A. fibers sweep anteriorly and downward and then progress posteriorly to primary visual cortex B. Meyer's Loop C. carries information from the superior retinal quadrants (i.e., inferior visual fields) D. terminate in V1 below the calcarine sulcus
C -- carries information from the *inferior retinal quadrants (i.e., superior visual fields)*
which of the following is NOT true: A. Type M and P ganglion cells project from the retina to specific layers of the LGN B. Type M project to layers 1-2 C. Layers 2, 3 and 5 receive input from the contralateral eye D. Type P project to layers 3-6
C -- layers *1, 4, and 6* note: main point is there are segregated parallel pathways that convey different visual information
which of the following is NOT processed by ventral stream of primary visual cortex (V1): A. color B. form C. motion D. object recognition
C -- motion (& visual guidance of movements) is processed by dorsal stream
which of the following corresponds to "Pupillary/visual light reflexes": A. lateral geniculate nucleus B. superior colliculus C. pretectal area D. suprachiasmatic nucleus
C -- pretectal area
which of the following retinal projections is NOT correctly matched to its function: A. To LGN in thalamus = Visual perception (retinothalamocortical projection) B. To Hypothalamus = Role in entraining circadian rhythms in day-night cycle C. To Superior colliculus = Process motion; visual guidance of movements D. To Pretectal area = Visual light reflexes
C -- sup colliculus = *Tectospinal tract* (reflexive head turning towards visual stimuli in periphery)
which of the following is NOT true of Spatial Distribution of Photoreceptors: A. spatial distribution of rods and cones is not uniform across the retina B. only cones are found in the fovea C. the density of receptors increases rapidly beyond about 20˚ D. rods are almost exclusively found beyond about 10˚ from the visual axis
C -- the density of receptors *declines* rapidly beyond about 20˚
which of the following is NOT true of Type P ganglion cells: A. Small ("parvo") dendritic fields B. Cones C. Process color, form and object recognition D. In periphery of retina
D -- *in fovea*
A lesion in right temporal lobe of Meyer's loop ((occlusion of R inferior MCA*) of the optic radiation would lead to: A. Right (ipsilateral) monocular blindness B. Bitemporal heteronymous hemianopsia C. Left (contralateral) homonymous hemianopsia D. Left superior (contralateral) quadrantanopia E. Left (contralateral) homonymous hemianopsia with macular sparing
D -- Left superior (contralateral) quadrantanopia ("pie in the sky visual cut") note: -- R temporal lobe of Meyer's loop of the optic radiation, which carries information from the *inferior retina from both eyes, i.e., superior visual field* -- Meyer's loop is supplied by inferior branches of the middle cerebral artery (whereas the parietal portion of optic radiation, which conveys contralateral inferior visual field, is supplied by superior branches of MCA -- a lesion confined the parietal portion results in inferior quadrantopia (i.e., "pie in the floor lesions")
which of the following is NOT true: A. Optic nerve is part of the CNS B. Optic nerve fibers originate in ipsilateral eye C. Optic nerves travel to optic chiasm where partial decussation takes place D. Optic tract fibers consist of nasal retinal fibers of ipsilateral eye and temporal retinal fibers of contralateral eye E. Optic tract fibers provide contralateral half of visual field for both eyes
D -- Optic tract fibers consist of *temporal* retinal fibers of ipsilateral eye and *nasal* retinal fibers of contralateral eye
which of the following is NOT a sign or symptom of MS: A. Optic neuritis B. Visual field defects C. Scotoma D. Papilledema
D -- false note: symptoms of optic neuritis = eye pain, decreased acuity, and impaired color vision; scotoma = alteration of visual perception in part of visual field 2˚ demyelination
which of the following is NOT processed by Type P ganglion cells: A. color B. form C. object recognition D. motion
D -- motion processed by *type M ganglion cells* note: Ventral stream of primary visual cortex (V1) → Occipito-temporal cortex → Process color, form, object recognition
which of the following corresponds to "Circadian rhythms": A. lateral geniculate nucleus B. superior colliculus C. pretectal area D. suprachiasmatic nucleus
D -- suprachiasmatic nucleus
Dorsal pathway (M pathway): -- Primary visual cortex to _____________ cortex -- Focuses on... Ventral pathway (P pathway): -- Primary visual cortex to _____________ cortex -- Focuses on...
Dorsal pathway (M pathway): -- Primary visual cortex → *parieto‐occipital cortex* -- *Where* in visual field an event occurred Ventral pathway (P pathway): -- Primary visual cortex → *occipito‐temporal cortex* -- *What* is the object in the visual field, and what is its *color* note: These two pathways are parallel and segregated from retina → LGN → V1
name the corresponding part of neocortex for dorsal and ventral streams, respectively
Dorsal stream → Posterior parietal cortex Ventral stream → Occipito-temporal cortex
compare the dorsal and ventral streams, respectively, of primary visual cortex (V1)
Dorsal stream → Posterior parietal cortex → Process motion; visual guidance of movements Ventral stream → Occipito-temporal cortex → Process color, form, object recognition
Lesion in right primary visual cortex would result in: A. Right (ipsilateral) monocular blindness B. Bitemporal heteronymous hemianopsia C. Left (contralateral) homonymous hemianopsia D. Left superior (contralateral) quadrantanopia E. Left (contralateral) homonymous hemianopsia with macular sparing
E -- Left (contralateral) homonymous hemianopsia, with macular sparing note: Macular sparing with primary visual cortex lesion is due to supplemental blood supply of the fovea region of V1 from branches of MCA; PCA and branch of MCA supply fovea = vascular redundancy → *macular sparing* https://www.youtube.com/watch?v=cG5ZuK0_qtc
which of the following is true of the Scototopic rod system: A. works at low levels of illumination B. "night vision" C. insensitive to color (monochromatic) D. lower resolution E. all of the above
E -- all of the above
T/F: presbyopia is the leading cause of blindness in the elderly
FALSE: *Age‐related macular degeneration* is
T/F: rods are densest in macula lutea with its center, the fovea, being the area of highest acuity vision
FALSE: *Cones* are densest in macula lutea with its center, the fovea, being the area of highest acuity vision
T/F: Both eyes have a blind spot; they overlap in the visual field
FALSE: Both eyes have a blind spot; they *do not overlap* in visual field
T/F: About one-third of neocortex of primates is devoted to processing some form of visual information
FALSE: Over 50% of neocortex of primates is devoted to processing some form of visual information (compared to 11% for somatosensory information and 3% for auditory information)
T/F: retinas have more cones than they do rods
FALSE: each retina has about 100 million rods (light sensitive) and 5 million cones (color sensitive)
T/F: in darkness, high cGMP concentrations allow Na+ channels to stay open and photoreceptors to generate action potentials
FALSE: photoreceptors *do not* generate action potentials note: DARK = high cGMP concentrations → keeps Na+ channels open → photoreceptor depolarization
define: -- Hemianopsia -- Quadrantanopia -- Homonymous -- Heteronymous
Hemianopsia -- refers to loss of one‐half of the visual field Quadrantanopia -- refers to loss of one quarter the visual field Homonymous -- denotes a condition in which visual field losses are similar for both eyes (e.g., left half of visual field for both eyes) Heteronymous -- denotes a condition in which the two eyes have non‐overlapping visual field losses (e.g., right half of visual field for left eye and left half of visual field for right eye)
Information processed from *lower* half of visual field → falls on _____________ half of retina → _____________ portions of primary visual field
Information processed from *lower* half of visual field → falls on *superior* half of retina → projects ipsi to *superior* portions of primary visual field note: vice versa is true
Meyer's loop carries information from the *inferior retinal quadrants (i.e., superior visual fields)* and terminate in V1 ____________ the calcarine sulcus. Axons carrying information from the *superior retinal quadrants (i.e., the inferior visual fields)* terminate in V1 _____________ the calcarine sulcus.
Meyer's Loop, inf retinal input → terminates below calcarine sulcus sup retinal input → terminates above calcarine sulcus
Neurons in LGN project to primary visual cortex. The ventral fibers sweep anteriorly and downward and then progress posteriorly to primary visual cortex. These projections form _________________.
Meyer's loop
Papilledema
Optic disc swelling 2˚ elevated intracranial pressure
For many people, one of the first signs of MS is *visual disturbances*. Why?
Optic nerve is a CNS tract, so it is subject to demyelination note: MS = demyelination of CNS
Right half of visual field seen by ______________ hemiretina of left eye and ______________ hemiretina of right eye Left half of visual field is seen by ______________ hemiretina of left eye and ______________ hemiretina of right eye
R half of visual field → L temporal hemiretina, R nasal hemiretina L half of visual field → L nasal hemiretina, R temporal hemiretina note: Fovea "sees" the central region of left and right visual fields
*** lesion of retina → lesion of high visual cortical area →
Retina lesion → V1 = blindness Higher visual cortical areas lesion = visual agnosia
RetinoGeniculoStriate projections
Retina → LGN (thalamus) → Primary visual cortex (V1, striate cortex, area 17)
the Scotopic rod system is used for ________ vision the Photopic cone system is used for ________ vision
Scotopic rod system -- night vision Photopic cone system -- day vision
T/F: rods are much more sensitive to light than cones
TRUE
T/F: visual acuity is better in fovea than in periphery of retina
TRUE
T/F: visual agnosia is NOT the same as blindness
TRUE
T/F: dorsal pathway communicates WHERE an object is, ventral pathway communicates WHAT an object is
TRUE note: -- dorsal (M) pathway to post-parietal cortex = motion, depth and spatial information -- ventral (P) pathway to inf temporal cortex = form and color
T/F: cyclic GMP concentrations are high in the dark and low in the light
TRUE note: -- LIGHT = decreased cGMP concentration → Na+ channels close → photoreceptor hyperpolarization -- DARK = increased cGMP concentration → keeps Na+ channels open → photoreceptor depolarization
T/F: the Visual system conveys more information to CNS than any other sensory system
TRUE note: Numerically, retinal photoreceptors represent about 70% of all sensory receptors in body
T/F: there are exclusively cones in the fovea of the retina, NO rods
TRUE note: fovea = highest visual acuity in this part of retina
T/F: each LGN gets input from *both* eyes
TRUE; Layers 1, 4, and 6 of LGN receive input from the contralateral eye
Type M ganglion cells (in periphery of retina) project to the magnocellular layers of the LGN (layers 1 and 2) and are concerned with... Type P ganglion cells (in fovea of retina) project to the parvocellular layers of the LGN (layers 3 through 6) and are concerned with...
Type M = patterns and contrasts Type P = color transmission
Photopic cone system
Works at higher levels of illumination (day time vision), color vision, high resolution high acuity
Scotopic rod system
Works at low levels of illumination (night vision), insensitive to color (monochromatic), lower resolution
macula lutea
an oval yellowish area surrounding the fovea near the center of the retina in the eye
Why is night sky seemingly not colorful?
because rods used for night vision are not sensitive to color
the _____________ is *only* area of blood redundancy in brain
fovea note: PCA and branch of MCA supply fovea → *macular sparing*
Retinal processing involves massive synaptic convergence onto ____________ cells
ganglion cells
Photon capture by photopigment leads to _____________________________ due to closure of Na+ channels. Photoreceptors do not generate action potentials.
graded hyperpolarization note: In light = photon activates opsin → activates transducin → activates → phosphodiesterase → decreases cGMP concentration → Na+ channels close → photoreceptor hyperpolarization
Why can you see stars best when not looking directly at them?
if look directly at star, falls on fovea and cones, so it disappears, versus if you look a little away the rods pick it up and we can see it better
inf occipital‐temporal area = fusiform face area =
inf occipital‐temporal area = color, face, letter and number recognition areas fusiform face area = face recognition
Projections from the ipsilateral eye terminate in layers ___, ___ and ___ of LGN Layers ___, ___ and ___ of LGN receive input from the contralateral eye
ipsilateral eye = 2, 3, and 5 contralateral eye = 1, 4, and 6
what is "V1"
just another name for primary visual cortex
‐anospia (‐anopia) refers to...
loss of one or more quadrants of a visual field
what is the name for the projection from LGN to primary visual cortex
optic radiation or geniculocalcarine tract
Contralateral homonynous hemianopsia is caused by lesions of __________________
optic tract
*** explain how optic tract fibers provide *contralateral* half of visual field for both eyes
optic tract fibers consist of temporal retinal fibers of ipsilateral eye and nasal retinal fibers of contralateral eye note: -- Visual info from left visual field of both eyes (right temporal hemiretina and left nasal hemiretina) → right side of brain (right optic tract, right LGN, right visual cortex) -- Visual info from right visual field of both eyes (right nasal hemiretina and left temporal hemiretina) → left side of brain (left optic tract, left LGN, left visual cortex)
retinal field
portion of retina that alters its firing rate in response to a stimulus note: there are reverse and inverted relationship between visual and retinal fields
visual field
portion of visual space that can be viewed from the retina when the eye is fixated straight ahead note: *each eye has a visual field*
*** Retinal Projections to LGN: Signals from each eye and from M & P pathways are *parallel and segregated pathways*; convergence does *not* occur until ______________________
primary visual cortex
Information processed by retina fovea → _________ part of primary visual cortex Information processed by periphery of the retina → _________ part of primary visual cortex
retina fovea → caudal primary visual cortex retina periphery → rostral primary visual cortex
The retina is organized into 10 histologically distinct layers. The photoreceptor layer is comprised of...
rods and cones
a lesion confined the parietal portion of optic radiation (occlusion of superior branches of MCA) results in... confined occlusion of the inferior branches of MCA result in...
superior branches of MCA → parietal portion of optic radiation (carries image from sup retina, inf field) → *inferior quadrantopia* ("pie in the floor") inferior branches of MCA → Meyer's Loop part of optic radiation (carries image from inf retina, sup field) → *superior quadrantopia* ("pie in the sky") https://www.youtube.com/watch?v=cG5ZuK0_qtc
describe general location of LGN
the LGN is in dorsal and caudal in the thalamus
describe RetinoGeniculoStriate Projection
using R visual field as example: info from R visual field (L temporal hemiretina & R nasal hemiretina) → L LGN → L primary visual cortex note: V1 is ipsilateral projection, so left and right V1 receives info about contra‐lateral half of visual field of both eyes (i.e., same as is the case for left and right LGN)