Audiology Lesson 2 - The Vestibular system

Question 1

Describe the functions of the vestibular system and its receptors

Answer 1

Maintenance of fixation and proper eye position during rapid head movements (VOR)

Maintenance of proper posture (acting against the force of gravity) (VSR)

Contribution to a proper sense of spatial orientation

RECEPTORS
- Maculae of the utricle and sacculus which since linear acceleration

• the crista ampullaris in the semicircular canals which sense angular acceleration

The hair cells are mechanoreceptors

The otoliths and gelatinous otolithic membrane together have a greater density than the endolymph. They are responsive to gravity and transmit their motion to the cilia of the sensory cells

Question 2

Fully describe the signal conduction of the hair cells in the vestibular system

Answer 2

AT REST
The stereocilia are arranged in rows of increasing height, with a single kinocilium at the tallest edge of the bundle

Tip-link proteins are ion channels that connect the cilia to each other

MOVEMENT
Depending on the direction of the ciliary movement of the sensory hair cells, the resting activity is altered by:

↑ discharge frequency (depolarization) - if the direction is toward the kinocilium

↓ discharge (hyperpolarization) - if the direction is opposite to kinocilium

NOTE: A constant discharge action potential passes along the vestibular nerve fibres even at rest - ‘resting activity’

Question 3

Describe how the vestibular nerve is divided

Answer 3

2 branches:

The superior branch
provides innervation to:
1. The superior and lateral (horizontal) semicircular canals
2. the utricle

The inferior vestibular nerve
provides innervation to:
1. the posterior semicircular canal
2. the saccule

Question 4

Describe the main vestibular efferents and what occurs when they malfunction

Answer 4

1. Vestibular-costical efferents which contribute to spatial orientation

2. Vestibulo-ocular reflex - to maintain fixation as the head moves (eyes move in opposite direction as head movement)
VOR involves 3 neurons:
- bipolar neurons of Scarpa's Ganglion
- Ipsilateral vestibular nucleus
- Oculormotor nuclei

When VOR malfunctions -> Nystagmus results (give explaination from neuro)

3. Otolith-ocular reflex and otolith-collic reflex: to maintainfixation during head tilt
   Neuro-otological sign: Ocular tilt reaction - can be abnormal with a unilateral vestibular deficit or unilateral brainstem lesion
   Characterized by:
   i. ipsilateral head and neck tilt
   ii. skewed deviation
   iii. ocular torsion
   Indicates either:
   i. a problem in the vestibular otolithic system
   ii. brainstem vascular problems (e.g. due to stroke)
4. Vestibular-spinal reflexes:
   For maintanance of proper posture

Question 5

List vestibular symptoms and signs and connect them with which vestibular function is affected

Answer 5

Spontaneous Nystagmus - problem in VOR

Vertigo and oscillopsia - related to loss of contribution of proper sense of spacial orientation

Impairment of upright posture and movement: problem in VSR

Question 6

Compare peripheral and central nystagmus

Answer 6

Peripheral:

• can be suppressed by fixation (frenzel goggles or penlight and disable this)
• usually comes with vertigo/oscillopsia

Central:

• Down and up-beat nystagmus (related to cerebellum)
• Nystagmus with no vertigo or oscillopsia
• Cannot be suppressed with fixation

Question 7

Name and describe the 3 main SYMPTOMS related to vestibular system disorders

Answer 7

Vertigo - Sensation of motion, pt feels their surroundings are whirling

Oscillopsia - Illusion that environment is moving when head is moved (due to bilateral vestibulopathy)

Dizziness - loss of balance, sensation of unsteadiness

Question 8

List the 4 main peripheral vestibular disorders

Answer 8

• Benign Paroxysmal Positional Vertigo
• Acute Unilateral Vestibular Loss
• Meniere Disease
• Vestibular Migraine

Question 9

Describe BPPV and include what you should ask the patient

Answer 9

1. Benign Paroxysmal Positional Vertigo (BPPV)
   Common.
   characterized by:
   - severe short lasting recurrent attacks of vertigo
   - triggered by particular movements of the head or body
   - Nystagmus induced by postural change

Pathological otoliths are free floating in the endolymph of the semicircular canals.
- We observe different types of nystagmus depending on which semicircular canal is affected

e.g. vertical-rotatory nystagmus is typical of a posterior semicircular canal involvement

• Is vertigo provoked by turning over in bed or when getting in or out of bed?
• Is the vertigo relatively short-lived and relieved by staying in one position?
• Have there been previous attacks?
• Has there been a recent provocation (trauma, dentist, prolonged bed rest)?
• Are there auditory symptoms? (hearing loss, tinnitus, fullness in the ear).

Question 10

Describe Acute unilateral vestibular loss and what to ask the patient if you suspect this

Answer 10

Defined as a sudden and severe attack of vertigo, with an inability to maintain upright posture
Less frequent than BPPV, but still very common

• very symptomatic (nausea, vomiting)
• Usually the symptoms subside in few days with spontaneous recovery of the equilibrium (vestibular compensation)

Caused by:
i. a vascular event
ii. a viral event
Characterized by horizontal-rotatory spontaneous nystagmus.

Ask patient:

• is vertigo continuous?
• Is vertigo worsened by movement?
• Any nausea/ vomiting?
• Recent viral infections?
• Any auditory symptoms?

Question 11

Describe Meniere’s Disease

Answer 11

It is a vestibular problem + hearing problem (affects both the vestibular and cochlear systems). Characterized by recurrent vertigo attacks with nausea and vomiting that last for minutes to hours

o typical history of fluctuating hearing loss (affects low frequencies)
o Examination of a patient during an attack of Meniere disease, usually yields a sensorineural HL involving the low frequencies
o aural fullness and tinnitus increase during vertigo attacks

IMPORTANT
Probably related to endolymphatic cochlear hydrops (relative overproduction or inadequate reabsorption of endolymph with distension of the cochlear duct)

Treatment: Gentamycin injection (antibiotic) via the tympanic membrane

You can ask pt:

• Is there pain/pressure/fullness in the ear?
• Is there a drop in hearing?
• Is there tinnitus?
• vertigo?
• previous history of attacks or drop attacks?

Question 12

What can you ask pt with vestibular migraine?

Answer 12

• History of migraine with aura?
• Family history of migraine?
• Light or noise sensitivity or headache?
• Nausea and vomiting?