Vestibular System

Question 1

Vestibular System Function

Name the 3 main functions of the vestibular system

Answer 1

1. Detection and conscious perception of head perception and movement
2. Compensatory eye movements during head movement in order to provide stabilisation of visual image and target fixation
3. Compensatory postural adjustments of the trunk and limb muscles following head movement

Question 2

Vestiublar system anatomy:

The vestibular system is connected with the spinal cord via which tracts? [2]

The vestibular system is connected with the cerebellum via the which lobe [1] and which nucleus [1]?

The vestibular system is connected to which CNs? [3]

Answer 2

The vestibular system is connected with the spinal cord via which medial and lateral vestibulospinal tracts

The vestibular system is connected with the cerebellum via the floccculonodular lobe and fastigial nucleus

The vestibular system is connected to CN III, IV & VI

Question 3

Vestiublar system anatomy:

Name the parts of the vestibular apparatus (that lie within the inner ear)

Answer 3

• semi-circular canals
• utricle (which lies at the base of the semi-circular canals)
• saccule

Question 4

Which of the following numbers depicted the vestibular tracts [1]

Answer 4

2c

Question 5

Label A-F

Answer 5

A: (Macula of) utricle
B: (Macula of) saccule
C: cochlea
D: posterior semilunar canal
E: Stapes
F: Malleus and incus

Question 6

Label

Answer 6

5 Cochlea
16 External acoustic meatus
17 Mastoid air cells
11 Posterior semicircular canal
(posterior canal)

Question 7

The vestibular system has five ense organs. List them

What type of

Question 8

Name and describe the function of the two types of solution found within the vesitubular apparatus.

Answer 8

Endolymph
* inside the semicircular canals and moves, and provides most of the signalling for the vestibular hair cells

Perilymph
* fills the scalae tympani and vestibuli.

Question 9

What is the difference in ion concentration between endolymph and perilymph? [2]

Answer 9

Perilymph: has similar concentrations of ions to plasma; high sodium and low potassium

Endolymph: extremely low sodium and high potassium

Question 10

Where in the vestibular system are vesitubular hair cells found? [3]

Answer 10

The ampulla, saccule and utricle is where vestibular hair cells are found.

Question 11

Describe how the semicircular canals function to detect angular acceleration/deceleration of the head

Answer 11

There are three semicircular canals: anterior, posterior, and lateral. located in a different plane and each connect to an ampulla (widening of the canal) which conncects to the utricle

Within each ampulla there are hair cells and cristae with a gelatinous cupula above the hair cells * crista

Each canal is a continuous endolymph filled loop, when the head rotates endolymph displaces the gelitinous cupula and excites the hair cells causing depolarisation or hyperpolarisation

Movement towards the kinocilium causes the opening of channels and a subsequent depolarization of the cell. Movement away from the kinocilium causes the closure of channels leading to hyperpolarization of nerve fibers.

Question 12

Semicircular canals

Describe how the hairs of the vestibular apparatus work in a push-pull rhythm

Answer 12

Each tuft of hair cells is polarised. If deflected one way it will be excited (if towards the direction rotation), if deflected the other will it will be inhibited

Thus, the canals on either side of the head operate in a push-pull rhythm; when one is excited the other is inhibited

Question 13

Label A & B [2]

Answer 13

A: utricle
B: saccle

Question 14

Describe the function of the utricle / saccle [1]

What is the macula of the utricle and saccle and what substance does it contain? [2]

Answer 14

Saccule and utricle is to keep the head vertically oriented with respect to gravity

Macula of utricle / saccle: cilia of hair cells embedded in a gelatinous mass.

Contains calcium carbonate crystals call otoliths

Question 15

What is the difference in function betweenthe utricle and saccule? [2]

Describe how the saccule and utricle keep the head vertically oriented with respect to gravity [3]

Answer 15

Utricle: longitudinal acceleration,
Saccule: acceleration along the vertical axis

Mechanism:
* otoliths provide the inertia, so that when movement to one side occurs, the otolith-gel mass causes the hair cells to deviate

• The hair cells are excited, or inhibited, by bending of the stereocilia towards or away from the kinocilium, just as the hair cells in the semi-circular canals
• Linear acceleration of the head causes a shear force between the otolithic membrane and macula, causing displacement of the hair bundles.

Question 16

Which direction are hair cells in the utrcile pushed during forward acceleration? [1]

Which direction are hair cells in the saccule pushed when a person descends?[1]

Answer 16

Utricle hairs pushed backwards during forward acceleration

Saccule hairs pushed upwards when person descends (gravitational force)

Question 17

Describe the head-righting reflex.

Answer 17

If the head and body start to tilt, such as when a student falls asleep in a lecture, the vestibular nuclei will automatically compensate with the correct postural adjustments via activation of the VSTs

Question 18

Describe the function of the vestibular-occular reflex

Answer 18

This reflex keeps the eyes fixed on a particular object when the rest of the body is in motion

Question 19

Describe how the VOR works

Answer 19

Automatically sensing head rotations and elicits a compensatory adjustment in the opposite direction of the eyes

Causes innervation on the medial-lateral rectus muscles (adduction / abduction), the inferior rectus-superior oblique pair (depression and extorsion, elevation and intorsion) and the superior rectus-inferior oblique pair (elevation and intorsion, depression and extorsion via the ascending medial longitudinal fasciulus

Question 20

The axonal connections between the vestibular and oculomotor nuclei that mediate the VOR travel in a tract called the []

Answer 20

The axonal connections between the vestibular and oculomotor nuclei that mediate the VOR travel in a tract called the medial longitudinal fasciculus (MLF)

Question 21

Primary afferent fibres from the vestibular apparatus terminate mainly in the []

A small number of fibres project directly into the []

Answer 21

Primary afferent fibres from the vestibular apparatus terminate mainly in the vestibular nuclei (in the medulla and pons)

A small number of fibres project directly into the vestibulocerebellum (flocculo-nodual node & uvula)

Question 22

What are the 4 nuclei that make up the vesitbular nuclei? [4]

Answer 22

• Lateral vestibular nucleus (LVN)
• Medial vestibular nucleus (MVN)
• Superior vestibular nucleus (SVN)
• Descending (inferior) vestibular nucleus (DVN)

Question 22

What are the 4 nuclei that make up the vesitbular nuclei? [4]

Answer 22

• Lateral vestibular nucleus (LVN)
• Medial vestibular nucleus (MVN)
• Superior vestibular nucleus (SVN)
• Descending (inferior) vestibular nucleus (DVN)

Question 23

Where do axons from the 4 vestibular subnuclei (LVN; MVN; SVN; DVN) project? [5]

Answer 23

1. Vestibulocerebellum
2. Thalamus and cortex
3. Reticular formation
4. Extraocular eye muscles
5. Spinal cord motor neurones

Question 24

# Central pathways of the vestibular system Where do the superior and medial vesibitular subnuclei recieve input from? [1] Where do the lateral, inferior and medial vesibitular subnuclei receive inputs from? [1]

Answer 24

superior and medial: **semi-circular canals** lateral, inferior and medial: **saccule and utricle** (together aka maculae)

Question 25

Where does input from the: **semi-circular canals** to the superior and medial vestibular subnuclei project to? [4] Where does input from the: **saccule and utricle** to the lateral, inferior and medial vesibitular subnucleii project to? [3]

Answer 25

Semi-circular goes to **ocular nuclei** and **reticular formation**, **gaze centres** and **tectal nuclei** (double check which pathways these are sent via) Saccule and utricle goes to **spinal motor nuclei** via the **lateral and medial VSTs**, which are involved in **postural balance**

Question 26

The superior and lateral vestibular nuclei also interact with which strucutre in the brain [] ?

Answer 26

The superior and lateral vestibular nuclei also interact with the **flocculo-nodular lobe of the cerebellum**

Question 27

Describe the neuronal connections that determine our conscious appreciation of equilibrium and head position.

Answer 27

Second order **vestibular neurones** project to the **contralateral ventral posterior nucleus** of the **thalamus**, and from there the **somatosensory cortex and posterior parietal cortex**.

Question 28

What is the name given to the region of the cortex where there is convergence of the vestibular and proprioceptive signals? What is important to rememver about this?

Answer 28

**Parietal insular vestibular cortex** Remember that this is responsible for the **contralateral side of the body/limb**.

Question 29

Name signs and symptoms oof vestibular dysfunction [5]

Answer 29

* A sensation of dizziness or vertigo * Falling or a feeling of falling (towards the dysfunctional side) * Light-headedness or feeling woozy (known as syncope) * Visual blurring * Disorientation * Spontaneous nystagmus * Ataxia

Question 30

Describe the features of benign paroxysmal positional vertigo (BPPV) [1] Describe the physiopathlogy behind BPPV? [1]

Answer 30

A brief, 60 second, intense sensation of vertigo that occurs because of a specific positional change of the head Dislodged otolith from the utricle, which then gets stuck in the ampulla, making it sensitive to gravity. In certain positions, the otolith can stimulate the cupula, causing abnormal sensations. These persist until the crystals relocate elsewhere or disperse

Question 31

Describe the symptoms of Menieres disease [3] Describe the pathophysiology of Menieres disease

Answer 31

Inner ear fluid balance disorder that causes episodes of **vertigo, fluctuating hearing loss, tinnitus** and the **sensation of fullness in the ear** Caused by an **imbalance** between the **production and reabsorption of endolymph**, which eventually **ruptures the membranes**, causing **changes in ion concentration of the solute**, leading to **depolarisation** of the **endolymph fluid**, ultimately **killing** the **hair cells.**

Question 32

An infection to which structure causes a labyrinthitis? [1] Name two symptoms [2]

Answer 32

* Labyrinthitis is an infection or inflammation of the **semi-circular canals** causing **dizziness and loss of balance**

Question 33

What is vestibular neuritis? [1] What is a perilymph fistula? [1]

Answer 33

* Vestibular neuritis is a **viral infection of the vestibular nerve** * Perilymph fistula is a **leakage of inner ear fluid into the middle ear**. It can occur after head injury or physical exertion, or is idiopathic

Question 34

Describe 6 tests that can be conducted to test for balance disorders [6]

Answer 34

* **Hallpike’s Manoeuvre**: With the patient lying in supine position, the head is lowered quickly below the horizontal plane of the table and turned to one side. The patient then sits up and the test is repeated, turning the head to the other side. If there is vestibular dysfunction, the patient will develop nystagmus and complain of vertigo within 10 seconds of head movement * **Audiometry** * **The caloric test**: weak nystagmus or the absence of nystagmus may indicate an inner ear disorder. The way to remember the correct response is COWS: cold water in the ear should cause the nystagmus to be away from this ear, whereas warm water causes the nystagmus to be flickering towards this ear * **Imaging of the head and brain** * **Posturography**: this requires the individual to stand on a tilt table, capable of movement within a controlled visual environment. Body sway is recorded in response to movement of the platform and/or visual environment * **Videonystagmography** * **Electronystagmography**

Question 35

Describe difference between cold water and warm water effect if conducting a caloric test

Answer 35

Direction of nystagmus & direction of water: **Cold Opposite, Warm Same**

Question 36

Label A

Answer 36

Otoliths

Question 37

The [] is more sensitive to **horizontal acceleration** in comparison to the [], which is more sensitive to **vertical acceleration**

Answer 37

The **utricle** is more sensitive to **horizontal acceleration** in comparison to the **saccule**, which is more sensitive to **vertical acceleration**