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Vestibular Physiology
Built from Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
What’s inside
15 sections · 153 slides
Overview
- Scope of this presentation
The vestibular sense
- Function of vestibular sensation
- Why the system is noticed only when it fails
Anatomy of the vestibular system
- The five vestibular end organs
- Anatomy of the labyrinth and its nerve supply
- Arrangement of the semicircular canals
- Orientation of the semicircular canals in the skull
- Orientation of the otoconial organs
- Bony and membranous labyrinth
- Perilymph and endolymph compartments
- Blood supply of the vestibular end organs
- Vestibular nerves and Scarpa's ganglion
- Territory of the superior and inferior vestibular nerves
- Posterior ampullary nerve and the singular canal
The vestibular hair cell
- The hair cell as primary functional unit
- Structure of the vestibular hair cell
- Tip links and mechanotransduction
- Bidirectional coding around a resting discharge
- Afferent firing rate versus stereocilia displacement
- Context determines the adequate stimulus
Sensory epithelium of canals and maculae
- Crista ampullaris and the cupula
- Structure of the semicircular canals
- Layers of the otoconial membrane
- Structure of the otoconial organs
- Polarity of the macular hair cells
- Force polarization vectors for cristae and maculae
Neurophysiology of the afferents
- Type 1 and type 2 vestibular hair cells
- Regular and irregular afferent discharge
- Selective vulnerability of irregular afferents
- Interpretation of interaural firing asymmetry
- Vestibular efferent fibres
Semicircular canal physiology
- Division of labour between the end organs
- Ewald's observations on canal stimulation
- Ampullopetal and ampullofugal excitation
- The unifying rule of canal excitation
- Relative motion of the cupula during head rotation
- Physiology of the semicircular canals during head rotation
- Coplanar canal pairs and push-pull organisation
- Ewald's second law: excitation exceeds inhibition
- Principles applied to head impulse testing
Otolith physiology
- How otoconia confer linear sensitivity
- Non-uniform macular activation
- Tilt-translation ambiguity
- Physiology of the otoconial organs
- Clinical relevance of the tilt-translation problem
Vestibular reflexes
- Foveal fixation as the goal of eye movements
- Why a vestibular reflex is required
- The angular vestibulo-ocular reflex
- Latency of the angular VOR
- Alignment of the extraocular muscles with the canal planes
- Three-neuron arc for horizontal head rotation
- Angular VOR during a horizontal head rotation
- Contribution of the inhibited contralateral canal
- Gain of the vestibulo-ocular reflex
- Oscillopsia
- The linear vestibulo-ocular reflex
- Linear vestibulo-ocular reflex and target distance
- Vestibulospinal and vestibulocollic reflexes
- Postural tone and the cervical VEMP
- Vestibular contribution to autonomic control
Central vestibular pathways
- Components of the central vestibular system
- Topography of vestibular nuclear projections
- Central projections from the vestibular periphery
- The vestibulocerebellum
- Surgical and clinical anatomy of the vestibulocerebellum
- Vestibular projections to the cerebral cortex
- Velocity storage
- Disorders of velocity storage
- The velocity-to-position neural integrator
- The leaky integrator after vestibular loss
Evaluating the dizzy patient
- Framework for the dizziness consultation
- Triage, TITRATE and test approach to dizziness
- Description of the complaint
- Localising value of the symptom quality
- Timing of the initial episode
- Duration of episodes by condition
- Precipitating factors and triggers
- Sound and pressure induced vertigo
- Chemical and situational triggers
- Associated visual symptoms
- Associated otological and neurological symptoms
- Comorbidity, medication and family history
Bedside examination: static imbalance
- Structure of the bedside vestibular examination
- Jerk nystagmus and its two phases
- Slow and quick phases of jerk nystagmus
- Spontaneous nystagmus after unilateral loss
- Why the pattern is horizontal-torsional
- Slow-phase eye movements from individual canal excitation
- Fixation suppression and how to unmask nystagmus
- Peripheral and central nystagmus at the bedside
- Alexander's law
- Alexander's law and Bruns' nystagmus
- Bruns' nystagmus
- Other forms of central nystagmus
- The ocular tilt reaction
- Testing for skew deviation
- Alternate cover test for skew deviation
Bedside examination: dynamic imbalance
- The clinical head impulse test
- Clinical head impulse test
- Head impulse testing of the vertical canals
- Post head-shaking nystagmus
- Mechanism and value of head-shaking nystagmus
- Dix-Hallpike manoeuvre
- Characteristic features of BPPV nystagmus
- Identifying the affected canal from gaze direction
- Lateral canal BPPV
- Lateralising lateral canal BPPV
- Superior canal BPPV and positional downbeat nystagmus
- Examination of posture and gait
- The Romberg test and its modifications
- Dynamic visual acuity testing
- Additional bedside manoeuvres
- Mechanism of hyperventilation-induced nystagmus
Vestibular physiology in everyday life
- Motion sickness
- Sensory conflict as the common stimulus
- Mal de debarquement syndrome
- Positional alcohol nystagmus
- Alcohol, magnetic fields, heights and microgravity
- Magnetic vestibular stimulation in MRI
- Acrophobia and visual height intolerance
- Height intolerance and the vestibular patient
- After-effects of spinning and amusement rides
- Vestibular function in microgravity
Summary
- Core principles of vestibular physiology
- Principles for the bedside
- References
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- Haynes-Glasscock-Shambaugh Surgery of the Ear, Seventh Edition
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