The vestibular system Flashcards
What medical term is used to describe instability?
Vestibular ataxia
What is the vestibulospinal reflex?
Reflex balance reaction to sudden instability of gait/ posture
What is the vestibulo-ocular reflex?
Reflex that preserves visual acuity during head-movement
Recall the vestibular system nerve supply of the extraocular muscles
Superior and medial vestibular neurons
Recall the pathway of the vestibulo-ocular reflex
Abducens nerve: abduction of one eye
CNVI excites contralateral oculomotor nucleus
Other eye adducted
Other than the vestibulo-spinal and vestibulo-ocular reflexes, name 3 functions of the vestibular system
- BP and HR control during rapid up/down tilts
- Synchronises respiration with body orientation
- Provoke motion sickness
What are the 2 principle components of the vestibular system?
Otolith organs
Semi-circular canals
What is sensed by the otolith organs?
- Acceleration of head
2. Strength + direction of gravity
What are the main components of the otolith organs?
Otolith hair cells
Saccule
Utricle
What is the saccule?
Bed of hair cells in inner ear
What is detected by the saccule?
Linear accelerations and head tilts in VERTICAL plane
What overlays the otolith hair cells?
Otoconia
Describe the cilia found on otolith hair cells
Each hair cell has one kinocilia and many stereocilia
Describe the directional sensitivity of otolith hair cells
All combinations of lateral and antero-posterior directions
What stimulates the otolith hair cells?
Internal resistance of the otoconia to head acceleration
Describe the orientation of the utricle and the cells within it
Oriented horizontally with hair cells projecting vertically
What is sensed by the semi-circular canals?
Angular rotation of head
From where do hair cells project in the semi-circular canals?
Ampullae
Describe how the semicircular canals differentiate acceleration and deceleration
Acceleration to the right stimulates canals on the right whilst deceleration to the right stimulates canals to the left, and vice versa
How do semi-circular canals ensure a balance of firing when the head is upright?
Fire at tonic firing rate
What are the semi-circular canals stimulated by?
Rotation in their own plane
What gives signal to the brain of linear acceleration in all 3D directions overall?
Vector sum of utricular and saccular patterns
Define vertigo
False perception of movement in space
Recall the normal neural pathway of vestibular projections
–> hypothalamus –> spatial cortex
Where is the spatial cortex?
Tempero-parietal region
Define oscillopsia
Inability to stabilise eyes during head movement in bilateral vestibular legion
Describe the main symptom of oscillopsia
Objects in visual field appear to oscillate
What is the main consequence of unilateral loss of vestibular function?
Severe nausea and vomiting
What medical term is given for an inability to stabilise the eyes?
Vestibular nystagmus
What causes vestibular nystagmus
One intact canal has an unopposed tonus
Describe the onset of visual nystagmus
Intact canal has an unopposed tonus –> eyes therefore driven to SIDE OF LESION as normal vestibulo-occular reflex
o Drifting movement is detected by the brainstem
intermittent “resetting” of eye position with fast saccades
rapid involuntary eye movement
Describe the onset of vertigo
• Tonus of the intact canal = signal that head is rotating to intact side
- causes feeling of intense spinning
Recall 2 symptoms of a bilateral vestibular lesion
Oscillopsia
Mild gait ataxia
