L15 - Vision & Balance(LA)

Question 1

T/F: Visual system has direct access to vestibular nuclei (involved in balance)

Answer 1

T

Question 2

Vection is an illusion of self-motion while stationary caused by? What types?

Answer 2

Moving visual scenes
Liner: like in a train
Circular: sitting in a rotating cylinder

Question 3

What happens when we rotate at a constant velocity?

Answer 3

The sense of rotation is gradually replaced by a sense that the world is rotating around us.

Question 4

If you place someone in a centrifuge - what do they associate verticality with? Gravity, centrifugal force, resultant force?

Answer 4

Resultant

*It is not gravity but FORCE in general with which we align our notion of what is “vertical”

Question 5

!How do we sense force? (4)

Answer 5

• Pressure on feet
• Other body parts may take weight
• Muscle reactions to maintain uprightness
• MAJOR SOUCE: vestibular apparatus inside inner ear

Question 6

!What are the 3 main sources of orientation info?

Answer 6

1) Visual orientation info
2) Proprioceptive info (joint position, muscle force (via sensors in tendons))
3) Vestibular system

Question 7

_ semicircular canals that sense? _ otolith organs that sense? Both in inner ear (each side of the head) found in?

Answer 7

3 - Rotation, angular acceleration
2 - Linear acceleration
Petrous portion of temporal bone (hardest bone in skull - but still vulnerable to infection)

Question 8

!How can vestibular system be disrupted?

Answer 8

Deaf people lack the system, may be destroyed by gentamycin or related antibiotics, viruses

Question 9

What is affected if vestibular system is disrupted?

Answer 9

Swimming (disrupts proprioceptive and visual sources of “up” info), standing on one foot, walking in the dark

Question 10

What is presbycusis?

Answer 10

Hearing loss

Question 11

What happens to vestibular organs when excessive physical activity occurs?

Answer 11

Damage to vestibular organs. High impact aerobics can injure otoliths

Question 12

Bony labyrinth of vestibular system contains?

Answer 12

Perilymph

Question 13

Membranous labyrinth of vestibular system contains?

Answer 13

Endolymph

Question 14

Vestibular nerve is part of CN_

Answer 14

8 - same as auditory nerve but different termini

Question 15

Where do hair cells of all the labyrinth organs send their output to?

Answer 15

Vestibular nuclei in brainstem

Question 16

Cell bodies of vestibular nerve cluster in?

Answer 16

Vestibular ganglia of Scarpa (a swelling of the vestibular nerve within the internal auditory meatus)

Question 17

Where does vestibular nerve send efferent input to?

Answer 17

Hair cells

Question 18

The 2 otolith organs (fluid filled sacs) are called?

Answer 18

• Utricle is joined to the 3 semicircular canals
• Saccule is a separate little pouch
• Oto (ear) lith (stone) - they are crystals of Ca2CO3

Question 19

Sensory hair cells embedded into otolith organs where the otoliths are embedded on top of it

Answer 19

Sensory hair cells embedded into otolith organs where the otoliths are embedded on top of it

Question 20

Auditory transduction
Bending towards kinocilium - depol
Away - Hyperpol

Answer 20

Auditory transduction
Bending towards kinocilium - depol
Away - Hyperpol

Question 21

Responses of kinocillium saturate when cilia are bent more than _ microns?

Answer 21

0.5 microns - about the width of a cilium

Question 22

What happens to otolith organs when airplane loses altitude in downdraft suddenly?

Answer 22

• Saccular up/down otoliths stimulated

- Utricular otoliths no longer press on hair cells

Question 23

Where are endolymph found?

Answer 23

Semicircular canals are filled with endolymph

Question 24

Each semicircular canal has a bulge called?

Answer 24

Ampulla

Question 25

Hair cells detect inertia of? Otoliths? Canals?

Answer 25

Hair cells - Internal contents
Otoliths - otoliths itself
Canals - Endolymph

Question 26

Cupula

Answer 26

Gelatinous mass on top of crista (thickened zone of epithelium) that contains hair bundles in the same orientation. Bending one direction hyperpol (away from kinocilium), other direction depol (towards kinocilium).

Question 27

During head rotation, the endolymph pushes on the?

Answer 27

Cupula

Question 28

Vestibular nerve transmits info about head rotation to vestibular nuclei in the medulla ipsilaterally or contralaterally?

Answer 28

Ipsilaterally

Question 29

Vestibulo-ocular reflexes

Answer 29

Keep eyes still when head moves

Question 30

Vestibulo-spinal reflexes

Answer 30

Enables skeletomuscular system to compensate for head movement and for head to be kept still while body moves

Question 31

!3 Different Vestibular-ocular reflexes (VOR) - what do they compensate for? Input from? Walking involves which ones?

Answer 31

1) Rotational (most important one) - compensates for head rotation. Canal input
2) Translational - Compensates for linear head movement. Otolith input
3) Ocular counter-rolling - compensates for head tilt in the vertical. Otolith input

Walking involves rotational and translation

Question 32

When the canals sense rotation in one direction, the eyes slowly rotate in the same/opposite direction? Does this occur in the dark?

Answer 32

Opposite, yes

Question 33

In horizontal rotation - what drives the slow phase? Fast phase?

Answer 33

Slow - vestibular signals

Fast - brainstem circuits

Question 34

What phase - slow or fast in horizontal rotation do comatose patients don’t have?

Answer 34

Fast

Question 35

3 neuron arc of horizontal VOR

Answer 35

1) Ear to vestibular nucleus
2) To eye movement nuclei
3) To eye

Question 36

Theories of motion sickness (2)

Answer 36

1) Sensory mismatch - e.g. reading book in car, your ear says moving but eyes say stationary. Drivers can anticipate motions, giving less mismatch
2) Poisons (e.g. alcohol) tend to produce mismatch between vision and balance by upsetting viscosity of ventricular endolymph - hence vomiting may be an adaptive response to ingesting poison

No explanation fits all the data

Question 37

Is Vection influenced by eye movements?

Answer 37

No

Question 38

What is better for predicting sickness - VA or duration of eye movements?

Answer 38

VA