Vestibular Systems

Question 1

Which structures in the body are responsible for angular (rotational) motion of the head?

Answer 1

Semi-circular canals

Question 2

Which structures in the body sense the acceleration of the head and the strength of gravity?

Answer 2

Otolith organs

Question 3

What are the two otolith organs?

Answer 3

Saccule

Utricle

Question 4

Define vertigo.

Answer 4

False perception of movement in space

Question 5

Define vestibular ataxia

Answer 5

Instability of gait or posture

Question 6

What are some other consequences of vestibular loss?

Answer 6

Slight impairment of orthostatic control
Severe nausea and vomiting
Loss of coordination on directional reorientation, motion intolerance, oversensitivity to visual motion in the environment

Question 7

What type of cell is involved in the detection of movement in the vestibular system?

Answer 7

Hair cells

Question 8

Describe the cilia of these hair cells.

Answer 8

There is one kinocilium and the rest are stereocilia

Question 9

What does the hair cell fibre synapse with and where does it project?

Answer 9

It synapses with a primary neurone dendrite (cell body in Scarpa’s ganglion)
They project to the vestibular nuclei in the brainstem

Question 10

What stimulates hair cells?

Answer 10

In Otoliths: deflection by forces of inertial resistance to acceleration
In Semi-circular Canals: endolymphatic fluid rotation

Question 11

Describe how the hair cell receptor potential can be changed.

Answer 11

Depolarisation = movement towards the kinocilium 
Hyperpolarisation = movement away from the kinocilium

Question 12

Describe how ganglion cell discharge can be changed.

Answer 12

Towards the kinocilium = increased firing frequency

Away from the kinocilium = decreased firing frequency

Question 13

Describe the orientation and sensitivities of the saccule.

Answer 13

Saccule is oriented vertically with the hair cells projecting normal to the plane
They are sensitive in all combinations of vertical and antero-posterior directions

Question 14

Describe the orientation and sensitivities of the utricle.

Answer 14

Utricle is oriented almost horizontally with the hair cells projecting vertically
Directional sensitivities in all combinations of lateral and antero-posterior directions

Question 15

Describe the structure and function of the semi-circular canals.

Answer 15

Hair cells project from the ampulla in the wall of the canal and are uni-directionally oriented so that acceleration to a particular side stimulates the canals on that side (e.g. rotation of the head to the right stimulates the right canal, rotation in the other direction inhibits the right canal activity)
When head rotation decelerates to a stop, the canal on the other side (left side) is stimulated

Question 16

Describe the firing of the canals when the head is still.

Answer 16

Each canal has a tonic firing rate so that they equal out when the head is still

Question 17

What are the effects of loss of canal function on one side?

Answer 17

There is unopposed signal coming from the intact side meaning that there is partial impairment of sensitivity to rotation in the ‘on’ direction of the defunct canal

Question 18

Why would a unilateral canal lesion cause vertigo?

Answer 18

The unopposed tonus of the intact canal gives a signal as if the head is rotating to the intact side.
Patient may feel like they’re spinning even though they’re not.

Question 19

Why would acute unilateral vestibular disorder cause vestibular nystagmus?

Answer 19

Unopposed tonus of the intact canal causes the eyes to be driven to the lesioned side – this is a vestibulo-ocular reflex (because it thinks that your head is rotating towards the intact side)

Question 20

Where do superior and medial vestibular neurones project?

Answer 20

They project to the motor nuclei supplying extraocular muscles.

Question 21

Describe the path of medial vestibular neurones.

Answer 21

The axons of medial vestibular neurones cross the midline and project to the contralateral abducens (VI) nucleus to abduct the eye on the opposite side (in the opposite direction to head rotation)
Axons from the abducens nucleus ascend in the MLF to the contralateral oculomotor nucleus (III) to adduct the other eye (in theopposite direction to head rotation)

Question 22

Describe the path of superior vestibular neurones.

Answer 22

Project ipsilaterally to the oculomotor and trochlear nuclei to generate
VERTICAL vestibulo-occular reflexes

Question 23

What is oscillopsia?

Answer 23

Everything appears to be oscillating
This is due to marked loss of vestibular function impairing eye stabilisation during rapid head movements.
The vestibulo-ocular reflex is lost.

Question 24

How would you test if a patient has oscillopsia?

Answer 24

Tell the subject to look at a fixed target and then rapidly move their head.
If they have bilateral loss of vestibular function then their eyes will be taken off target by the head swing.

Question 25

What are the effects of bilateral vestibular disorder on gait?

Answer 25

Mild gait ataxia

Question 26

What are the effects of unilateral vestibular disorder on gait?

Answer 26

Tendency for the body and head to lean or fall to the lesioned side

Question 27

Describe the path and function of the lateral vestibulo-spinal tract.

Answer 27

Descends ipsilaterally in the ventral funiculus of the spinal cord Axons terminate in lateral part of ventral horn Influence motor neurones to limb muscles

Question 28

Describe the path and function of the medial vestibulo-spinal tract.

Answer 28

Descend bilaterally in MLF to cervical and upper thoracic spinal cord Axons terminate in medial part of ventral horn Influence motor neurones to back and neck muscles

Question 29

State a common cause of vestibular vertigo that lasts: a. Seconds b. Minutes c. Hours d. Days e. Fluctuating/continuous f. Silent

Answer 29

``` a. Seconds Benign Paroxysmal Positional Vertigo (BPPV) b. Minutes Vertebrobasilar insufficiency c. Hours Meniere’s Syndrome d. Days Vestibular neuritis e. Fluctuating/continuous Uncompensated vestibular lesion f. Silent Acoustic neuroma ```

Question 30

Inputs to vestibular system

Answer 30

Vision Pressure in feet Inner ear for info on rotation and gravity

Question 31

Outputs of vestibular system

Answer 31

Ocular reflex | Posture control

Question 32

What bone is inner ear in

Answer 32

Petrus part of temporal as hardest

Question 33

How many organs to vestibular system per ear

Answer 33

5

Question 34

Otilith organs of vestibular system

Answer 34

Sacculus | Utricals

Question 35

What does sacculus connect to

Answer 35

Superiorly utricle and inferiorly cochlea

Question 36

What are 3 other organs to system

Answer 36

Lateral Posterior Superior canals

Question 37

What do 3 canals connect to

Answer 37

Utricle

Question 38

What fluid is in vestibular organs

Answer 38

Endolymph

Question 39

What fluid is between organ and bone

Answer 39

Perilymph

Question 40

What do each semi circular canals have

Answer 40

They have 2 canals leading to utricle | For each defined canal there is one wide and one narrow canal

Question 41

What is name given to wider canals

Answer 41

Ampulla

Question 42

Comparison of anterior and posterior canal planes

Answer 42

90 degrees | Purposefully orientated

Question 43

Types of hair cells in vestibular organ

Answer 43

Type 1 and 2

Question 44

Differences between type 1 and 2

Answer 44

More of type 1 Type 1 has indirect efferent but type 2 has direct Afferents all direct

Question 45

Where are hair cells in sacula

Answer 45

Side part nearest cochlea

Question 46

Where are hair cells in utricle

Answer 46

At bottom

Question 47

What plane does utricle deal with

Answer 47

Horizontal

Question 48

What plane does sacula deal with

Answer 48

Vertical

Question 49

What are otoliths

Answer 49

Carbonate cristals

Question 50

Name given to functional component of otoliths

Answer 50

Maculae

Question 51

Components of maculae

Answer 51

Hair cells Gelatinous matrix Otoliths

Question 52

Where is gelatinous matrix

Answer 52

On top of hair cells

Question 53

Purpose of gelatinous matrix

Answer 53

AIDS hair cell movement

Question 54

Where are otoliths

Answer 54

On matrix

Question 55

How are hairs stimulated

Answer 55

If moved in one way they trigger stimulatory pathway and in other an inhibitory pathway

Question 56

What is striola

Answer 56

Central part of maculae | Either side of it the orientation of cilia in opposite direction

Question 57

Where are hair cells in semicircular canals

Answer 57

Ampulla

Question 58

Where is cupula

Answer 58

Ampulla

Question 59

What is the cupula

Answer 59

A gelatinous mixture more dense than endolymph

Question 60

Direction of hair cells in ampulla

Answer 60

All in one direction unlike otoliths | Mirroring instead occurs between ears

Question 61

Name of functional part of ampulla

Answer 61

Crista

Question 62

Supply of blood to vestibular system in inner ear

Answer 62

Basilar artery-> anterior inferior cerebrellar artery -> labyrinthine

Question 63

Divisions of vestibular nerve

Answer 63

Inferior and superior

Question 64

Where does vestibular nerve go

Answer 64

Vestibular nuclei

Question 65

Organisation of vestibular nuclei

Answer 65

Lateral and inferior deal with static labyrinth | Medial and superior deal with kinetic labyrinth

Question 66

Where do vestibular nuclei project

Answer 66

Spinal chord Cerebellum Nuclei of extraocular muscles Cardiovascular and respiratory centres

Question 67

Tracts for vestibulospinal reflexes and place innervated

Answer 67

Medial vestibulospinal tract- upper back and neck | Lateral vestibulospinal tract- limbs and trunk

Question 68

Vestibulocerebrellar reflex goes where and via what

Answer 68

Vestibulo cerebellum via inferior cerebrellar peduncle

Question 69

Where does vestibulo-ocular reflex travel to and via what

Answer 69

Oculumotor, abducens and trochlear nucleus via medial longtitudal fasiculus

Question 70

Route from vestibular nuclei to vestibular cortex

Answer 70

Medial leminiscus to ventroposterior nucleus to vestibular cortex via internal capsule

Question 71

Physiology of hair cell potentials

Answer 71

Tips open k+ channels depolarising the cell, leads to ca2+ influx which binds to vesicles

Question 72

Resting discharge of hair cells

Answer 72

Tonic activity of hair cells If excited then more frequent impulses due to depolarisation If inhibited then less frequent impulses due to hyperpolarisation Same applies to ones in cochlea

Question 73

Effect of acceleration on hair cells

Answer 73

Acceleration causes hairs to shift in opposite direction to acceleration as endolymph moves gelatinous matrix

Question 74

How semicircular canals work between ears

Answer 74

They are paired

Question 75

Pairings of left and right semicircular canals

Answer 75

Lateral both together Left anterior and right posterior Right anterior and left posterior LARP and RALP

Question 76

Way of remembering parings

Answer 76

Ralp and Larp

Question 77

Lateral vestibulospinal pathway

Answer 77

Lateral vestibular nucleus down lateral vestibulospinal tract to influence ipsilateral limb movements

Question 78

Medial vestibulospinal tract pathway

Answer 78

From medial vestibular nucleus down medial vestibular tract to upper thoracic and cervical levels as supplies trunk and neck muscles

Question 79

Differences between lateral and medial vestibulospinal pathways

Answer 79

Medial is bilateral (ipsilateral pathway more dense)

Question 80

Purpose of having hairs in 2 directions

Answer 80

Can send same signal twice but in different way | One being that the hairs have been stimulated and other being that they have been inhibited

Question 81

Vestibuloocular reflex features

Answer 81

Aims to keep image fixed so ensure eye movements in opposite direction to head movement Fastest reflex in the body

Question 82

Vestibulo ocular pathway horizontal

Answer 82

Lateral SCC-> scarpas ganglion->vestibular nucleus-> abducens nucleus-> up medial longtitudal fusiculus-> occulomotor nucleus-> lateral and medial rectus

Question 83

Vestibulo ocular pathway vertical

Answer 83

Anterior SCC-> scarpas ganglion->vestibular nucleus-> abducens nucleus-> up medial longtitudal fusiculus-> occulomotor nucleus-> superior oblique

Question 84

Common symptoms of vestibular issues

Answer 84

Vertigo Dizziness Unsteadiness Issues of movement perception