Ch. 16: Vestibular and Visual Systems

Question 1

Lesions to optic Radiations

Answer 1

• hemianopsia or quadrantanopsia

- loss of info from contralateral visual field

Question 2

Lesion to optic chiasm

Answer 2

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

Question 3

Lesion to optic tract

Answer 3

• homonymous hemianopsia

- loss of visual info from one visual hemi-field

Question 4

Lesion to optic nerve

Answer 4

• blindness

- ipsilateral eye

Question 5

Hair cells

Answer 5

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

Question 6

canals & vision

Answer 6

• inner ear connected to eye movement

- stabilize vision when head is moving

Question 7

semicircular canals

Answer 7

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

Question 8

paired activity

Answer 8

-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

Question 9

otolithic organs

Answer 9

• 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

Question 10

Input to vestibular nuclei

Answer 10

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

Question 11

outputs from vestibular nuclei

Answer 11

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

Question 12

superior colliculus

Answer 12

• reflexive head movements in response to vision

- orientation and visually guided eye movement

Question 13

L Visual Cortex sees:

Answer 13

Right visual field

Question 14

R visual cortex sees:

Answer 14

L visual field

Question 15

Dorsal Action Stream

Answer 15

• light from occipital cortex to motor planning area

- visually guide movements

Question 16

visual pathway

Answer 16

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)

Question 17

Pretectal area

Answer 17

• parasympathetic neurons here

- pupillary light reflex connects here

Question 18

tectum

Answer 18

where colliculi sit

Question 19

2 pathways from visual cortex

Answer 19

• dorsal action stream

- ventral action stream

Question 20

Ventral perception stream

Answer 20

• occipital cortex to inferior temporal lobe

- to visually identify and name object visually

Question 21

Gaze stabilization

Answer 21

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

Question 22

Conjugate vs disconjugate

Answer 22

• conjugate: both eyes move together and coordinated

- Disconjugate: not together or coordinated

Question 23

VOR

Answer 23

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

Question 24

2 functions of eye movement

Answer 24

• gaze stabilizatoin

- direction of gaze

Question 25

direction of gaze

Answer 25

- move eyes to focus on object of interest - connection from occipital cortex to eye Mm - mostly conscious--visually driven

Question 26

2 Reflexes of gaze stabilization

Answer 26

- vestibulo-ocular reflex (VOR) | - optokinetic reflex

Question 27

optokinetic reflex

Answer 27

- during slow head movements - more conscious - eye adjusts when object falls out of visual field

Question 28

smooth pursuit

Answer 28

- eyes move smoothly when tracking an object | - test with H test

Question 29

Damage to visual/vestibular system due to damage to:

Answer 29

- peripheral receptors - CN - Brain stem nuclei - central projection axons - cortical reception areas - patterns--> clues about what's damaged

Question 30

saccades

Answer 30

- voluntary vs reflexive - eyes move from one point of focus to another with head still - jumpy - used with reading

Question 31

Nystagmus

Answer 31

- 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

Question 32

general s/sx vestibular disorder

Answer 32

- vertigo - nausea - nystagmus - disequilibrium - postural instability - impaired gaze stabilization - oscillopsia

Question 33

oscillopsia

Answer 33

- complete loss of visual stabilization - vision bounces like COPS camera - due to decreased VOR

Question 34

unilateral peripheral hypofunction

Answer 34

-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

Question 35

Unilateral peripheral hyperfunction

Answer 35

- 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

Question 36

Bilateral peripheral hypofunction

Answer 36

- both ears send fewer signals than appropriate | - S/Sx: severely decrease gaze stabilization (oscillopsia); significan postural instability; no dizziness/nausea

Question 37

lesion to occipital cortex

Answer 37

- cortical blindness | - no awareness of visual info