Ch. 16: Vestibular and Visual Systems Flashcards
Lesions to optic Radiations
- hemianopsia or quadrantanopsia
- loss of info from contralateral visual field
Lesion to optic chiasm
- bitemporal hemianopsia
- loss of info from both temporal visual fields
- interruption to axons of nasal half of each retina
Lesion to optic tract
- homonymous hemianopsia
- loss of visual info from one visual hemi-field
Lesion to optic nerve
- blindness
- ipsilateral eye
Hair cells
- inside base of canals in fluid
- at rest, send certain # action potentials
- bent one way=increase #
- benth other way= decrease #
canals & vision
- inner ear connected to eye movement
- stabilize vision when head is moving
semicircular canals
- anterior=45*
- posterior=45*
- horizontal=tipped 30* (ant more superior)
paired activity
-increased action potential # toward side of rotation and decreased proportionately on complementary side
- Complimentary sides:
- -horizontal-horizontal
- -L ant-R post
- -R and-L post
otolithic organs
- base of canals (hair cells in gel with rocks on top)
- respond to linear movement and pull of gravity
- modulate postural muscle activity in response to movement or gravity
Input to vestibular nuclei
- collect info from every sensory system that senses movement
1. vestibular info
2. visual info
3. proprioceptive info
4. tactile info
5. auditory info
outputs from vestibular nuclei
- medial vestibulospinal tract (helper neurons)
- lateral vestibulospinal tract (helper neurons)
- spinal accessory nerve IX
- cerebral cortex
- medial longitudinal fasciculus
- reticular formation (nausea/vomiting)
- cerebellum
superior colliculus
- reflexive head movements in response to vision
- orientation and visually guided eye movement
L Visual Cortex sees:
Right visual field
R visual cortex sees:
L visual field
Dorsal Action Stream
- light from occipital cortex to motor planning area
- visually guide movements
visual pathway
- retina
- optic N (CN II)
- optic chiasm
- Optic tract
A. pretectal area (reflexive pupillary)
B. superior colliculus (reflexive head movement)
C. Occipital cortex (conscious sight)
Pretectal area
- parasympathetic neurons here
- pupillary light reflex connects here
tectum
where colliculi sit
2 pathways from visual cortex
- dorsal action stream
- ventral action stream
Ventral perception stream
- occipital cortex to inferior temporal lobe
- to visually identify and name object visually
Gaze stabilization
- keeps eyes focused on object when head moving
- connection from inner ear to CN
- almost always unconscious
Conjugate vs disconjugate
- conjugate: both eyes move together and coordinated
- Disconjugate: not together or coordinated
VOR
- keep world/eyes steady while head moves
- all directions/during fast head movement
- automatic/unconscious
- important for postural stability during movement
2 functions of eye movement
- gaze stabilizatoin
- direction of gaze
direction of gaze
- move eyes to focus on object of interest
- connection from occipital cortex to eye Mm
- mostly conscious–visually driven
2 Reflexes of gaze stabilization
- vestibulo-ocular reflex (VOR)
- optokinetic reflex
optokinetic reflex
- during slow head movements
- more conscious
- eye adjusts when object falls out of visual field
smooth pursuit
- eyes move smoothly when tracking an object
- test with H test
Damage to visual/vestibular system due to damage to:
- peripheral receptors
- CN
- Brain stem nuclei
- central projection axons
- cortical reception areas
- patterns–> clues about what’s damaged
saccades
- voluntary vs reflexive
- eyes move from one point of focus to another with head still
- jumpy
- used with reading
Nystagmus
- physiologic/pathologic
- due to difference in activity in paired semicircular canals
- physiologic: after spinning (eye slips opposite of movement and jumps to catch up)
- Pathologic: occurs with no appropriate stimulus
general s/sx vestibular disorder
- vertigo
- nausea
- nystagmus
- disequilibrium
- postural instability
- impaired gaze stabilization
- oscillopsia
oscillopsia
- complete loss of visual stabilization
- vision bounces like COPS camera
- due to decreased VOR
unilateral peripheral hypofunction
-1 ear sending fewer signals than appropriate
Ex. Vestibular neuritis–action potentials from CN VIII on one side mismatches signals from other
S/Sx: decrease gaze stabilization (especially when turning to affected side); postural instability; dizziness; nausea
Unilateral peripheral hyperfunction
- 1 ear sends more signals than appropriate
- Ex. BPPV-crystals in canals cause inappropriate excitation; feel like moving when still
- S/Sx: dizziness, nausea, decrease gaze stabilization and postural stability
Bilateral peripheral hypofunction
- both ears send fewer signals than appropriate
- S/Sx: severely decrease gaze stabilization (oscillopsia); significan postural instability; no dizziness/nausea
lesion to occipital cortex
- cortical blindness
- no awareness of visual info
