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Year 2 LCRS > Neurology 11 - Vestibular System > Flashcards

Neurology 11 - Vestibular System Flashcards

1
Q

Compare type 1 and type 2 hair cells

A
  • More type 1 cells
  • Type 1 cells have direct afferents and indirect efferents, with a round shape
  • Type 2 cells have direct afferents and efferents. More efferents than afferents
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2
Q

What are striola?

A
  • Opposing hair bundle polarities/direction - the central part of the maculae
  • Movement in any direction stimulates a distinct subset of cells
  • Two movements from the same stimuli
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3
Q

List the components of the semicircular canals

A
  • Ampulla (hair cells in the crista) - one side only
  • Gelatinous projection - less dense than in the utricle and saccule (cupula)
  • Kinocilia (all in the same direction, as cells are oriented in the opposite direction on each side)
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4
Q

Describe the blood supply of the vestibular system

A
  • Anterior inferior cerebellar artery from the basilar artery gives rise to the labyrinthine artery
  • Labyrinthine artery splits to the anterior vestibular artery and common cochlear artery
  • Common cochlear artery splits to vestibulococchlear artery and main cochlear artery
  • Vestibulocochlear artery splits to form cochlear ramus (joins the cochlear ramus) and posterior vestibular artery which forms arteries of the canals
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5
Q

Describe the nervous supply of the vestibular system

A
  • Primary afferents end in the vestibular nuclei and in the cerebellum
  • Vestibular nuclei - this is where all vestibular reflexes origionate from (superior, lateral, medial and inferior)
  • Organised as static labyrinth (otoliths lateral and inferior) and kinetic labyrinth (semicircular canals superior and medial)
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6
Q

List the vestibular nuclei projections

A
  • Spinal cord
  • Nuclei of the extraocular muscles
  • Cerebellum
  • Centres for cardiovascular and respiratory control
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7
Q

List the functions of the vestibular system

A
  • Movement coordination (providing spatial reference for other sensory motor co-ordinations)
  • Posture regulation
  • Tuning cardiovascular function for reorientations
  • Perception of motion in space
  • Vestibular ocular reflex modulation (compensatory reflexes)
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8
Q

List the projections of the vestibular nucleus involving the thalamus and cortex

A
  • Vestibular nuclei: project to thalamus
  • Thalamic nuclei: project to the head region of the primary somatosensory cortex
  • Also to superior parietal cortex: ‘vestibular cortex’ concerned with spatial orientation.
  • Cortical projections may account for feeling of dizziness (vertigo) during certain kinds of vestibular stimulation
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9
Q

List the functions of the vestibular system

A
  • Detect and inform about head movements
  • Keep images fixed in the retina during head movements
  • Postural control
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10
Q

What are the otolith organs?

A
  • Utricule and saccule
  • Linear acceleration and tilt (otolith movement)
  • Depolarisation or hyperpolarisation
  • Utricule is horizontal
  • Saccule is vertical
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11
Q

How do the semicircular canals work?

A
  • Respond to angular acceleration by movement of endolymph moving the hair cells. Constant velocity is not felt (inertia).
  • Work in pairs (one side is stimulated while the other side is inhibited)
  • Both horizontal (lateral)
  • Left anterior to right posterior
  • Right anterior to left posterior
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12
Q

Describe the vestibulospinal reflex pathways

A
  • Lateral vestibulospinal tract (ipsilateral, motor neurones to limb muscles)
  • Medial vestibulospinal tract (bilateral, motor neurons to the neck and back muscles)
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13
Q

What is the function of the vestibulo-ocular reflex?

A
  • Keep images fixed while the head is moving
  • Connection between the vestibular nuclei and oculomotor nuclei
  • 5-7 msec latency
  • Eye movement in opposite direction to head movement
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14
Q

How are vestibular diagnoses made?

A
  • Medical history
  • Cranial nerves
  • Balance and gait assessment
  • Cerebellum
  • Gaze assessment
  • Vestibular tests (caloric test, vHIT, VEMP, rotational test)
  • Imaging (CT/MRI)
  • Subjective assessment (questionnaires, useful in long term disease)
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15
Q

List the symptoms of vestibular disease

A
  • Vertigo (illusion of movement - rotational or true)
  • Nystagmus (eye movement, slow movement and fast compensation)
  • Dizziness, giddiness
  • Unsteadiness
  • Self-motion perception
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16
Q

Describe the epidemiology of dizziness

A
  • 1/4 of people experienced it
  • 80% severe enough to see a doctor
    1/2 in 75+
  • 1/4 referrals to ENT and neurology clinics
17
Q

Where are peripheral vestibular disorders located?

A
  • Labyrinth and VIII nerve (vestibulococclear)
  • Vestibular neuritis
  • Benign paroxysmal positional vertigo
  • Menieres disease
  • Bilateral vestibular failure
  • Unilateral vestibular failure
18
Q

Where are central vestibular disorders located?

A
  • CNS

- Stroke, MS, tumours

19
Q

Describe the evolution of vestibular disorders

A
  • Acute (vestibular neuritis and stroke)
  • Intermittent (benign paroxysmal positional vertigo)
  • Recurrent (Menieres disease, migraine)
  • Progressive (aucoustic neurona, degeneration)
20
Q

What else, other than vestibular disease, can cause dizziness?

A
  • Heart disorders
  • Presyncopal episodes
  • Orthostatic hypotension
  • Anaemia
  • Hypoglycaemia
  • Psychological
  • Gait disorders
21
Q

What is the vestibular system?

A
  • Everything there is to balance
  • Inputs are visual, rotation and gravity (inner ear), and pressure (proprioception)
  • Output is the ocular reflex and postural control
22
Q

What is the outer ear?

A
  • What you see

- Eardrum, bones and ausicles

23
Q

What is the labyrinth?

A
  • The inner ear
  • It is in the petrous part of the temporal bone (hardest bone of the body)
  • Cochlear part and vestibular part
  • 5 structures generate the vestibular organ
24
Q

Describe the structure of the vestibular organ

A
  • 2 otoliths called the utricle and sacculus
  • Sacculus is connected to the cochlea and utricule is connected to the sacculus.
  • Posterior, anterior and lateral semicircular canals.
  • Each semicircular canal has an ampulla
  • Fluid is inside the ear (function is to move the hair cells in response to sound, and also change in movement)
25
Q

Describe the arrangement of the labyrinth in the skull

A
  • Cochlear is anterior
  • Semicircular canals are lateral
  • Anterior (also called superior) canals are 45 degrees
  • Posterior (also called inferior) canals are 45 degrees apart
26
Q

Describe the structure of the utricle and saccule.

A
  • Utricle (inferior - detects movement of the horizontal plane) and saccule (cochlear side - transduce movement of vertical plane)
  • The rest of the utricle and saccule contrain onle liquid
  • Macule (has the hair cells)
  • Gelatinous matrix is on top of the hairs - helps to move the hairs
  • Otoliths are on top of the gel matrix
27
Q

What are otoliths?

A

Carbonate cristals on top of the hair cells

28
Q

Describe the vestibular nuclei pathways

A
  • Hair cells send signals to vestibular nuclei to generate spinal reflexes (vestibulospinal tract - limb and trunk and upper back and neck)
  • Also goes to cortex (ventroposterior nucleus to vestibular cortex)
  • Vestibulo-ocular reflex (oculomotor, abducens and trochlear)
  • Cerebellum (vestibulocerebellar reflexes)
29
Q

Which parts of the cerebellum are involved in the maintenance of balance and control of eye movement?

A
  • Vermis

- Flocconodular lobe

30
Q

Describe the activation of the hair cells

A
  • Stimulus causes movement of the hair cells
  • Influx of potassium
  • Depolarisation
  • Calcium influx and neurotransmitter release
  • Resting discharge
  • Inhibition and excitation affect the rate of discharge
31
Q

Describe the pathway of the vestibuloocular reflex (horizontal)

A
  • Information comes from the vestibular nucleus to both sides, telling you which way the head is moving
  • The side the head moves towards has an increase in frequency
  • 3rd and 6th cranial nerves are stimulated (abducens and oculomotor nerve)
  • One muscle is stimulated and the other is inhibited
32
Q

Which muscles are involved in the vertical vestibuloocular reflex?

A
  • Superior rectus muscle and inferior rectus

- Superior oblique and inferior oblique muscle

33
Q

What happens in peripheral unilateral lesions?

A
  • No resting discharge from one side of the labyrinth
  • Therefore, the brain thinks that the head is moving towards the direction of the discharge
  • The eyes are therefore moved towards the opposite side
  • The eyes say the head is not moving, this results in movement of the eye from one side to the other (slow movement with fast compensation)
34
Q

Define dizziness

A

The sensation of spinning around and loosing your balance

35
Q

Define vertigo

A

The illusion of movement

36
Q

Define oscillopsia

A
  • Can be caused by nystigmus
  • Jumping vision and trouble focusing
  • Inability to hold images steady - objects look like they are moving even when they are stationary
37
Q

What is bilateral vestibulopathy?

A
  • Vestibular system of both inner ears is damaged
  • Symptoms include imbalance (which is worse in the dark) and visual disturbance
  • Oscillopsia occurs when the head is moving (objects appear to be moving when they are not moving)
38
Q

Describe signalling in the otolith organs

A
  • Macula of the utricle and saccule contain vestibular hair cells (each have a kinocilium, which is a long sterocilia, and sterocilia)
  • Stereocilia project to the otolithic membrane (a calcium bicarbonate cristal filled gel layer - otoconia)
  • Vestibular hair cells synapse with the vestibular nerve
  • When gravity pulls down the otoconia/linear acceleration moves them, this moves the stereocilia and kinocilium projecting into the layer as well
  • This opens ion channels and causes depolarization thereby creating an AP (depending)
  • Gives an idea of linear acceleration and gravitational head position
39
Q

Describe signalling in the semicircular canals

A
  • Each filled with endolymph
  • When you move your head to the left the SCC will move the same direction but the fluid will move to the right
  • This moves the cupula, a structure in the ampulla of each SCC containing vestibular hair cells thereby stimulating the vbestibular nerve
  • Gives an idea of angular acceleration

Year 2 LCRS (128 decks)

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