Ch. 16: Vestibular and Visual Systems Flashcards

1
Q

Lesions to optic Radiations

A
  • hemianopsia or quadrantanopsia

- loss of info from contralateral visual field

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2
Q

Lesion to optic chiasm

A
  • bitemporal hemianopsia
  • loss of info from both temporal visual fields
  • interruption to axons of nasal half of each retina
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3
Q

Lesion to optic tract

A
  • homonymous hemianopsia

- loss of visual info from one visual hemi-field

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4
Q

Lesion to optic nerve

A
  • blindness

- ipsilateral eye

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5
Q

Hair cells

A
  • inside base of canals in fluid
  • at rest, send certain # action potentials
  • bent one way=increase #
  • benth other way= decrease #
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6
Q

canals & vision

A
  • inner ear connected to eye movement

- stabilize vision when head is moving

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7
Q

semicircular canals

A
  • anterior=45*
  • posterior=45*
  • horizontal=tipped 30* (ant more superior)
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8
Q

paired activity

A

-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
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9
Q

otolithic organs

A
  • 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
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10
Q

Input to vestibular nuclei

A
  • collect info from every sensory system that senses movement
    1. vestibular info
    2. visual info
    3. proprioceptive info
    4. tactile info
    5. auditory info
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11
Q

outputs from vestibular nuclei

A
  1. medial vestibulospinal tract (helper neurons)
  2. lateral vestibulospinal tract (helper neurons)
  3. spinal accessory nerve IX
  4. cerebral cortex
  5. medial longitudinal fasciculus
  6. reticular formation (nausea/vomiting)
  7. cerebellum
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12
Q

superior colliculus

A
  • reflexive head movements in response to vision

- orientation and visually guided eye movement

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13
Q

L Visual Cortex sees:

A

Right visual field

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14
Q

R visual cortex sees:

A

L visual field

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15
Q

Dorsal Action Stream

A
  • light from occipital cortex to motor planning area

- visually guide movements

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16
Q

visual pathway

A
  1. retina
  2. optic N (CN II)
  3. optic chiasm
  4. Optic tract
    A. pretectal area (reflexive pupillary)
    B. superior colliculus (reflexive head movement)
    C. Occipital cortex (conscious sight)
17
Q

Pretectal area

A
  • parasympathetic neurons here

- pupillary light reflex connects here

18
Q

tectum

A

where colliculi sit

19
Q

2 pathways from visual cortex

A
  • dorsal action stream

- ventral action stream

20
Q

Ventral perception stream

A
  • occipital cortex to inferior temporal lobe

- to visually identify and name object visually

21
Q

Gaze stabilization

A
  • keeps eyes focused on object when head moving
  • connection from inner ear to CN
  • almost always unconscious
22
Q

Conjugate vs disconjugate

A
  • conjugate: both eyes move together and coordinated

- Disconjugate: not together or coordinated

23
Q

VOR

A
  • keep world/eyes steady while head moves
  • all directions/during fast head movement
  • automatic/unconscious
  • important for postural stability during movement
24
Q

2 functions of eye movement

A
  • gaze stabilizatoin

- direction of gaze

25
Q

direction of gaze

A
  • move eyes to focus on object of interest
  • connection from occipital cortex to eye Mm
  • mostly conscious–visually driven
26
Q

2 Reflexes of gaze stabilization

A
  • vestibulo-ocular reflex (VOR)

- optokinetic reflex

27
Q

optokinetic reflex

A
  • during slow head movements
  • more conscious
  • eye adjusts when object falls out of visual field
28
Q

smooth pursuit

A
  • eyes move smoothly when tracking an object

- test with H test

29
Q

Damage to visual/vestibular system due to damage to:

A
  • peripheral receptors
  • CN
  • Brain stem nuclei
  • central projection axons
  • cortical reception areas
  • patterns–> clues about what’s damaged
30
Q

saccades

A
  • voluntary vs reflexive
  • eyes move from one point of focus to another with head still
  • jumpy
  • used with reading
31
Q

Nystagmus

A
  • 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
32
Q

general s/sx vestibular disorder

A
  • vertigo
  • nausea
  • nystagmus
  • disequilibrium
  • postural instability
  • impaired gaze stabilization
  • oscillopsia
33
Q

oscillopsia

A
  • complete loss of visual stabilization
  • vision bounces like COPS camera
  • due to decreased VOR
34
Q

unilateral peripheral hypofunction

A

-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

35
Q

Unilateral peripheral hyperfunction

A
  • 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
36
Q

Bilateral peripheral hypofunction

A
  • both ears send fewer signals than appropriate

- S/Sx: severely decrease gaze stabilization (oscillopsia); significan postural instability; no dizziness/nausea

37
Q

lesion to occipital cortex

A
  • cortical blindness

- no awareness of visual info