Equilibrium + Posture 1 (Vestibular System)

Question 1

What are the 3 main contributors to orientation??

Answer 1

Vision (visual space)
Vestibular system (inertial space)
Proprioception (internal space)

Question 2

On a basic level, what is the vestibular system good at in terms of vision?

Answer 2

Very good at detecting motion (optic flow).

Prevalent with fairground illusions

Question 3

What is the inner ear considered as?

Answer 3

The organ of balance

Question 4

What are otoliths concerned with??

Answer 4

Concerned with linear acceleration/tilt

Question 5

What are semicircular canals concerned with?

Answer 5

Concerned with angular velocity

Question 6

How does movement affect sensory hair cells (exist on both otoliths and canals)

Answer 6

Causes a deflection of the hairs

Question 7

What do the stereocilia on hair cells do??

Answer 7

Motion towards the stereocilium depolarises the receptor and hence increasing firing rate of the afferent

Question 8

Discuss the push-pull action of left-right signals.

Answer 8

Rotation or acceleration is signalled by the difference in firing rate between the 2 ears.
Loss of one ear results in a strong sense of rotation causing vertigo and dizziness

Question 9

Provide a broad description of the utricle and succule structure?

Answer 9

Contain endolymph
Receptors in the macula
Respond to acceleration and gravity
Systematic variation in direction of polarisation 
Slow adaptation
Main role is postural stabilisation 

Utricle is approx horizontal when head is upright
Succule is approx vertical when head is upright

Question 10

The semicircular canals are perpendicular to each other, therefore can what?

Answer 10

Detect rotation in any direction

Question 11

The cupula is neutrally buoyant, what does this mean??

Answer 11

Typically the cupula is the same density as the surrounding endolmyph fluid, and therefore does not respond to changes in orientation (e.g., when lying down)

Question 12

What is positional alcohol nystagmus??

Answer 12

Upon alcohol ingestion, the cupula becomes lighter than the surrounding fluid. Therefore rises when laying down - which produces a left-beating nystagmus when lying on left ear

Question 13

What occurs after heavy water ingestion?? (D20)

Answer 13

The cupula becomes heavier than the surrounding fluid, therefore sinks when lying down -> produces a right beating nystagmus when lying on left ear

Question 14

How is stabilisation of gaze achieved??

Answer 14

Via vestibular input from both sides of the head

Question 15

How do the canals operate in unison?

Answer 15

In a push-pull manner, where head rotation causes excitation of one side, inhibition of the other

Question 16

What is the key signal for rotation of the head??

Answer 16

Asymmetry of the firing rate from both ears

Question 17

What is caloric vestibular stimulation?

Answer 17

A method of modulating the firing rate of the primary vestibular afferents, by irrigation of the ear canal with warm or cold water

Question 18

What occurs with warm H2o irrigation?

Answer 18

Increased firing mimics head turn towards the irrigated ear

Question 19

What occurs with cold H2o irrigation??

Answer 19

Decreased firing means mimics head turn away from the irrigated ear

Question 20

Galvanic vestibular stimulation?

Answer 20

A non-invasive method for altering vestibular nerve activity

Typically bipolar binaural and generally well tolerated, motion sickness is unusual

Question 21

What is the site of activation of GVS?

Answer 21

GVS bypasses end organs

Question 22

Wha is the Virtual Signal?

Answer 22

The firing rate of all vestibular afferents is modulated.

The resultant signal of roll about an axis in the Sagital plane directed approx 18. upward from Reid’s plane is predicted

Question 23

How does GVS evoke torsional eye movements?

Answer 23

Modulated firing rate causes torsional eye movements by activating the VOR

Question 24

Does the GVS evoke a balance response?

Answer 24

Yes, the direction of the turn is sensitive to the orientation of the head

Question 25

What does Delbaere et al (2010) state about fear of falling?

Answer 25

That fear of falling is causally linked to falling itself in older adults

Question 26

What did Osler et al (2013) find when inducing fear in young healthy participants

Answer 26

Showed increased sympathetic arousal at height
Overall GVS response reduced at height
Found sway to be identical up to ~800ms

Concluded that fear does not influence feed-forward gain of vestibular reflex