Visual System Flashcards
Retina
rods - peripheral
cones - central
fovea - point of fixation, highest visual acuity
Visual Fields
normal vision - 60% overlap
light from temporal visual on nasal retina (VICE VERSA)
CN 2 fibers from nasal retina cross optic chiasm (carry info about contra side)
Lateral Geniculate Nucleus
relay nucleus of thalamus
Optic Radiations (geniculocalcarine tract)
fibers arise from LGN through retro and sublenticular portion of internal capsule Meyer's Loop retinotopically organized (superior fibers represent inferior visual field)
Meyer’s Loop
passes through temp lobe
represent superior visual field
Visual Cortex
terminate in cortex adjacent to calcarine fissue (superior field below fissure - VICE VERSA)
contra visual field represented
B occipital damage can lead to cortical blindness
Visual Cortex Areas
17 - primary visual cortex
18, 19 - visual association cortex
Hemianopia
loss of half of visual field
Quadranopia
loss of one quadrant of visual field
Homonymous
overlapping visual fields (i.e. R visual field of both eyes)
Heteronymous
nonoverlapping field from each eye
Superior Colliculus Pathway
receives direct retinal input from visual, SS, and auditory inpts
projects to reticular formation (generate saccades) and C-spine (orients head via TS tract, decussates in MB)
functions to orient head and eyes to visual (mostly), SS, and auditory stimuli
lesion = inability to orient to contra visual stimuli
Retinohypothalamic Fibers Pathway
directly from retina
influence circadian rhythms
Pupillary Light Reflex Pathway
tests integrity of connection between di and MB
circuit for direct response – retina (sensory) –> optic nerve –> optic tract –> pretectum –> CN III (motor)
for consensual response, fibers cross in pretectum to opposite side CN III
Dorsal Stream
motor control, to post parietal cortex (ambient vision)
action vision, “where” pathway
info from fovea and retinal periphery = guide actions, about object characteristics
can operate in dim light
motor planning
Ventral Stream
more conscious awareness of visual experience; to inferotemporal cortex (focal vision)
perception vision, “what” pathway
info from fovea
needs good lighting
conscious perceptual experience of vision, recognition of objects
Lesion
Ventral - visual agnosia
Dorsal - optical ataxia
- can’t reach for object or adjust grasp to shape of object
- can pick object up but unaware of object’s dimensions or orientation
Visual Proprioception
where we are relative to environment
post parietal lobe
optical flow provides info about environment
Hypothalamus
influences behavior and autonomic, visceral, and pituitary function
Thalamus: general
almost all sensory pathways relay in thalamus, then relays to cortex
motor from Cb and BG, inputs from limbic area
receive feedback information from areas to cortex to which they project
Thalamus: topographical subdivisions
internal medullary lamina - divides into med/lat, splints ant
intralaminar nuclei - within IML, related to consciousness and pain transmission
lateral group - dorsal tier, ventral tier (VA, VL, VPL, VPM)
LGN and MGN - post extension of ventral tier, lateral (visual) medial (auditory)
Post Thalamic Lesions
thalamic pain - similar to trigeminal neuralgia (i.e. intense pain triggered by SS stimuli
affects 1/2 body, resistant to analgesics
total or nearly total loss of sensation of contra heady and body (hemi-sensory analgesia)
DCML most severely affected; some recovery
produces sensory ataxia
Thalamic Syndrome
contra thal pain, hemianesthesia, sensory ataxia
Internal Capsule
between thal, caudate (medial), and lentiform nucleus (lateral)
ant limb - between lenticular nucleus and head of caudate
post - between lenticular nucleus and thal
genu - between ant and post limbs
blood supply by penetrating brances of mostly MCA - lenticulostriate arteries (some post cerebral)
Internal Capsule: fibers
ant limb - carries to frontal cortex and from limbic portions of thal
post - ascending motor and sensory fibers (ventral tier, VPL - BG and Cb), descending CB and CS fibers
Internal Capsule Stroke
post limb effected
hemiparesis and hemianesthesia can result - pure because no accompanying cognitive deficit
contra pure motor hemiplegia, hemisensory syndrome
contra homonymous hemianopia
with small areas involved - dysarthria and clumsy hand
VA/VL - afferent, efferent
A - BG, Cb
E - supplemental and premotor motor areas
VPL - afferent, efferent
A - DCML, ST tracts
E - area 3,1,2
VPM - afferent, efferent
A - trigeminal system
E - area 3,1,2
Lat Gen - afferent, efferent
A - optic tract
E - area 17
Med Gen - afferent, efferent
A - BS auditory tracts
E - area 41
ILN - afferent, efferent
A - ST/RF/ARAS
E - all areas of cortex, striatum
