Vestibular System

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Functions

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VESTIBULAR + VISUAL + PROPRIOCEPTIVE SYSTEMS

I. Maintenance of fixation and proper eye position during rapid head movements

II. Maintenance of a proper posture (acting against the force of gravity)

III. Contribution to a proper sense of spatial orientation

Front 2

Anatomy: central pathways

Back 2

- Utricle, superior and horizontal semicircular canal -> SUPERIOR VESTIBULAR NERVE

- Inferior semicircular canal and saccule -> INFERIOR VESTIBULAR NERVE

- Vestibular nerves -> Vestibular (Scarpa) ganglion, lying near the fundus of the internal auditory canal -> joined by cochlear nerve to form the CN VIII -> running in the facial canal with CN VII -> ventral splitting after the pontomedullary junction and termination in the four Vestibular nuclei, Cerebellum and Reticular formation.

In the hippocampus and amygdala we have the cognitive perception of balance.

Front 3

Anatomy: utricle, saccule, macula

Back 3

Utricle: senses horizontal linear acceleration

Saccule: senses vertical linear acceleration

Macula:

Sensory organ of utricle and saccule.

It contains hair cells with cilia embedded in gelatinous layer containing calcium carbonate otoliths, which move in the opposite direction with respect to head movement.

The hair cells have 50-70 stereocilia each and one large kinocilium. By altering their firing rate and synapsing with the vestibular nerve, they communicate head movements. (Gravity)

Front 4

Anatomy: semicircular canals

Back 4

- Canals: Horizontal, posterior, superior. At right angles to one another.

- Ampulla: dilation at the end of each semicircular filled with endolymph. It contains the crista ampullaris, which has hair cells with cilia that project into a gel cup called cupula

- Cristae: they detect angular acceleration because fluid in the ducts stays relatively still from inertia despite head rotation

Front 5

Physiology of potential transmission in CN VIII

Back 5

The potential difference between the sensory cells & the extracellular fluid, forms the physiologic basis for a normal functioning of the system.

A constant discharge action potential, passes along the vestibular nerve fibers, even when the end organs are at rest (“resting activity”).

There is a structural difference between a kinocilium having a microtubular arrangement, and stereocilia which don’t have microtubules, instead they have actin cores. The stereocilia are arranged in rows of increasing height, with a single kinocilium at the tallest edge of the bundle.

Depending on the direction of the ciliary deflection of the sensory hair cells, the resting activity is altered by an increase in the discharge frequency (depolarization) or by inhibition (hyperpolarization).

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Vestibular efferents

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1. VESTIBULO-CORTICAL EFFERENTS: Contribute to spatial orientation

2. VESTIBULO-OCULAR REFLEX (VOR) Maintenance of fixation and proper eye position during rapid head movements

3. OTOLITH-OCULAR REFLEX & OTOLITH-COLLIC REFLEX Maintenance of fixation during head tilt:

OCULAR TILT REACTION - Ipsilateral head & neck tilt - Skew deviation - Ocular torsion

Deficits of OTR:

- Unilateral peripheral vestibular deficit (otolithic system)

- Unilateral lesion of brainstem pathways (from the vestibular nuclei to the interstitial nucleus of Cajal in the rostral midbrain).

4. VESTIBULOSPINAL REFLEXES (VSR) Maintenance of a proper posture (stability of the neck, trunk and limbs against gravity forces)

- Medial Vestibulo-Spinal tract: Cervical axial muscles - upper limbs

- Lateral Vestibulo-Spinal tract Lower limbs.

Front 7

VOR

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THE VOR INVOLVES 3 NEURONS:

1. BIPOLAR NEURON OF SCARPA ’ S GANGLION

2. IPSILATERAL VESTIBULAR NUCLEUS

3. OCULOMOTOR NUCLEI

Since there is a resting activity, if one of the two sides is not working, the one which is working will be firing also at rest, tricking the brain -> nystagmus, defined by the direction of the slow phase (if there is a right lesion, the brain will think that we are moving the head to the left and the slow movement will be directed towards the lesioned side, i.e. the right)

Front 8

Signs and symptoms of vestibular disorder

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I. Loss of contribution to a proper sense of spatial orientation -> Vertigo and oscillopsia

II. Loss of maintenance of fixation and proper eye position during rapid head movements -> spontaneous nystagmus

III. Loss of maintenance of a proper posture (acting against the force of gravity) -> Impairment of upright posture and movement

VERTIGO:

Sensation of motion in which the individual or the individual’s surroundings, seem to whirl.

OSCILLOPSIA:

The illusion that the environment is moving, while we are moving are head. It is the characteristic visual symptom when the vestibular function is lost (bilateral vestibular hypo-areflexia).

DIZZINESS: Sensation of unsteadiness, loss of balance. It may be of vestibular or extra-vestibular origin.

Front 9

Features of a central nystagmus

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- Down or up beating

- No vertigo or oscillopsia

- No visual inhibition of nystagmus

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Diagnosis

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Frenzel goggles:

• Disable the patient's ability to visually fixate on an object

• Allow the examiner to adequately visualize the eyes, using high-powered lens (+20 diopters) with an illumination system.

Penlight cover test:

• Shine a penlight in the right eye while intermittently occluding the left one

• Low-cost method to unmask Nystagmus by removal of visual fixation

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Vertigo

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• Third leading cause of access in the emergency department.

• Second symptom after pain

• 20-30% of the population

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Benign paroxysmal positional vertigo

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Severe recurrent attacks of vertigo, short lasting, triggered by particular movements of the head / body.

Peripheral disorder related to the pathological otoliths floating in the endolymph of the semicircular canals.

Most common canal: posterior semicircular.

Vertical-rotatory nystagmus evoked after a latent period. Determined by particular movements of the head. It increases for some seconds and then diminishes.

• Is it provoked by turning over in bed or when getting in or out of bed? -> YES

• Is the actual vertigo relatively short-lived and relieved by staying in one position? -> YES

• Have there been previous attacks? -> YES

• Has there been a recent provocation (trauma, dentist, prolonged bed rest)? -> YES

• Are there auditory symptoms? (hearing loss, tinnitus, fullness in the ear) -> NO!

Front 13

Acute unilateral vestibular loss

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Sudden and severe attack of vertigo, inability to maintain upright posture, nausea, vomiting. The symptoms subside in a few days with spontaneous recovery of equilibrium (vestibular compensation). (this is the same presentation of labyrinthitis)

Etiopathogenesis: viral (“neuritis”), vascular.

Horizontal-rotatory nystagmus increased by visual fixation.

Suppressed with Frenzel glasses

• Is there continuous vertigo, even when lying or sitting relatively still? -> YES

• Though it will still be made worse by movement of any type (not just turning over in bed) -> YES

• Is there considerable nausea, vomiting? -> YES

• Has there been a recent viral illness? -> YES/NO

• Are there auditory symptoms? (hearing loss, tinnitus, fullness in the ear) -> NO, unless labyrinthitis

Front 14

Meniére disease

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Recurrent vertigo attacks with nausea and vomiting which last for minutes-hours (30 minutes - 12 hours. Not more).

Typical history with fluctuating hearing loss (usually the low frequencies), aural fullness and tinnitus that increase during vertigo attacks.

Pathogenesis: endolymphatic cochlear hydrops that involves a relative overproduction or inadequate reabsorption of endolymph with distension of the cochlear duct.

Treatment: 90% respond to intratympanic injection of gentamicin, which is ototoxic. In nonresponders, we cut the vestibular nerve.

• Is there pain, pressure, fullness in the ear with, or preceding the vertigo?

• Is there a drop in hearing? -> YES, but only during the attack

• Is there tinnitus (low-frequency, sea shell)?

• Is there a previous history of similar attacks, or of drop attacks? -> YES

• Is there continuous vertigo, even when lying or sitting relatively still?

• Is there considerable nausea, vomiting?

• How long do the attacks last ?

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Vestibular migraine

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A diagnosis of exclusion. Criteria:

(1) Episodic vestibular symptoms of at least moderate severity – vertigo; positional dizziness and head motion intolerance

(2) Migraine according to International Headache Criteria

(3) One or more of the following features during at least two vertigo attacks – migrainous headache – headache – photophobia – phonophobia – migraine aura

(4) Other diagnoses excluded by appropriate tests

• Is there a history of migraine headaches (with aura, visual or otherwise), even in the remote past?

• Is there a family history of migraine or of recurrent attacks of vertigo?

• Is there light or noise sensitivity or headache? - Note, in ‘vestibular migraine’ the headaches and vestibular symptoms commonly occur separately.

• Do sleep, darkness help? • Is there nausea or vomiting?