Vestibular System Flashcards
What are the labyrinth organs?
Semi-circular canals – stimulated by ANGULAR acceleration.
- This gives a signal of approx. angular velocity
Otolith organs – stimulated by LINEAR acceleration and GRAVITY force
- This gives a signal of head acceleration and tilt
Describe the afferents and efferents of the types of hair cells
type 1
direct afferents
indirece efferent
*more in number
type 2
direct afferents and efferents
What are the otolith organs?
There are 2 otolith organs:
- Utricle – senses movement in the horizontal plane
- Saccule – senses movement in the vertical plane
The otoconia is a layer of calcium carbonate on top of a gelatinous layer and as it is heavy, movements of the head displace the otoconia and thus pull the hair cells
Linear acceleration will also move the heavy otoconia layer
There is ONE kinocilium per hair cell and movements towards the kinocilium stimulate the cell whilst movements away from the kinocilium do not.
These organs are OMNI-DIRECTIONAL.
What are semi-circular canals?
There are 3 semi-circular canals and these each join into an ampulla (hair cells in crista) that contains a capula full of hair bundles
Displacement of endolymph in the canals will move the capula and thus fire off APs from the hair cells
Linear acceleration produces equal force each side of the capula so there is no net movement
When the head turns left for example, the movement is towards the kinocilium in the horizontal canal in the left ear but in the right ear it is away from the kinocilium -> hence there is a depolarisation in the left ear and a hyperpolarisation (inhibition) in the right ear
There is a constant tonic firing when at rest.
Which artery supplies the inenr ear?
Anterior inferior cerebellar artery
*also goes to cerebellum and other parts of the brain - stroke can affect ear
What are the vestibular nuclei? How are they organised?
static labyrinth (otoliths) - lateral and inferior
kinetic labyrinth (SCC) - superior and medial
Where do the vestibular nuclei project to?
spinal cord
nuclei of extraocular nuscles
cerebellum
centres for cardiovascular + respiratory control
What happens in the thalamus and cortex?
vestibular nuclei project to thalamus
thalamic nuclei projects to head region of primary somatosensory cortex
also tosuperior parietal cortex - ‘vestibular cortex’ concerned with spatial orientation
*cortical projections may account for feeling of dizziness during certain kinds of vestibular stimulation
What are the functions of the vestibular system?
to detect and inform about head movements
to keep images fixed in the retina during head movements
postural control
What happens in the otolilth organs with different types of movements?
linear accelerations and tilt : otolilth movement
otolilth movement : depolarisation or hyperpolarisation
ultricle = horizontal saccule = verticle
How does movement affect the semi-circular canals?
angular acceleration endolymph inertia culpa moves and displaces hair cells superior and inferior SCC: (+) away from utricle horizontal SCC: (+) towards utricle
What is the vestibulospinal reflex?
lateral vestibulospinal tract
- ipsilateral
- motor neurons to limb muscles (goes to lumbar area)
medial vestibulospinal tract
- bilateral
- motor neurons to neck and back muscles (doesn’t go to lumbar area)
What is the vestibulo-ocular reflex?
function - to keep images fixed
connection between vestibular nuclei and occulomotor nuclei
around 8mseg latency
eye movement in opposite direction to head movement
What is nystagmus?
Acute unilateral vestibular disorder – the unopposed tone of the intact canal causes the eyes to be driven to the lesioned side (vestibular-ocular reflex)
The movement is detected by the brainstem which then corrects eye position with fast movements
- This effect is minimised by visual suppression mechanisms.
How do you diagnose nystagmus?
- anamnesis (history)
- balance and gait assessment
- cerebellum
- gaze assessment : eye movements
- vestibular tests (caloric test, vHIT, VEMP, rotarional test)
- imaging ( CT, MRI)
- subjective assessment (questionnaires)
