Neuro - Vestibular System Flashcards
What are the main inputs of the vestibular system
Visual
Proprioceptive (pressure)
Vestibular (rotation and gravity)
What is the role of the CNS in the vestibular system
Processes inputs and integrates them to generate responses
What are the outputs of the vestibular system
Ocular reflex and postural control to keep an image fixed when we move, and to stop us falling over when moving
Where is the vestibular organ found
In the posterior area of the middle ear
What does the inner ear contain?
Hair cells for hearing and balance
What makes up the vestibule
The utricle and saccule make up the vestibule which us the entrance to the inner ear
What joins the utricle and saccule
A conduit
What is the saccule joined to
Cochlea
What are the semicircular canals connected to
These each have an ampulla on one side and are connected to the utricle
What is the need for having the semicircular canals in different planes
This gives us planes so that specific structures are stimulated with specific head movements. This means that we can have more focused reflexes to help maintain our ocular reflex and postural control
What is the kinocilium
The biggest cilium, typically found adjacent to other stereocilia
How does depolarisation of vestibular hair cells arise?
When the head moves, the liquid inside the inner ear (endolymph) moves and causes hair cell deflection either towards or away from the kinocilium. Stereocilium movement towards the kinocilium means that we get depolarisation
What does greater head movement mean in terms of depolarisation?
Greater head movement leads to greater hair cell deflection and thus greater depolarisation
What are otolith organs
Utricle and saccule both otolith organs
Where are the hair cells of the utricle located
In the maculae found horizontally
Where are the hair cells of the saccule located
In the maculae found vertically
What do the maculae contain
Contain the hair cells, a gelatinous matrix and then the otoliths on top
What are otoliths
Carbonate crystals that help with the movement of hairs
Where are hair cells in canals located
Located in the crista ampullaris (of the ampulla)
What is the cupula
Surrounds the hair cells and help hair cell movement by closing the ampulla so that endolymph can move it to help with the deflection of hair cells
Where do primary afferents for the vestibular nerve end up
In the vestibular nuclei and the cerebellum
Where do the vestibular nuclei project?
Spinal cord
Nuclei of the extra ocular muscles
Cerebellum
Centres for cardiovascular and respiratory control
What are the 4 vestibular nuclei
Superior
Inferior
Medial
Lateral
What reflexes are produced by vestibular afferents travelling via the vestibular nuclei
Vestibulospinal reflexes
Vestibulocerebellar reflexes
Vestibulo-ocular reflex
What is the vestibular cortex
Not one specific area - as many inputs and integrators are involved there are several cortical areas which partake
What is the main area of the vestibular cortex
Parieto-Insular Vestibular Cortex (PIVC) found in the parietal lobe
What are the 3 main functions of the vestibular system?
Detect and inform about head movements
Keep images fixed in the retina during head movement
Postural control
What are the 3 potentials of hair cells
Resting potential
Excitations
Inhibition
Describe the resting potential of hair cells
When we are upright there is still some firing in order to maintain postural control therefore we say there is basal discharge
What does hair cells moving towards the kinocilium generate?
Depolarisation and an increase in nerve discharge
What does hair cells moving away from the kinocilium generate?
Hyperpolarisation and a reduction in nerve discharge
When one side of the vestibular system is depolarised, what happens to the other side?
When one side is depolarised, the other side is inhibited as we are sending the same info to the vestibular nuclei
What causes otolith movement?
Linear acceleration and tilt
What generates basal discharge when the head is upright
When we are upright we still have some deflection of hair cells therefore we get a basal discharge in order to keep us upright
What type of movement is the utricle sensitive to
Horizontal movement
What type of movement is the saccule sensitive to
Vertical movement
What does depolarisation/ hyperpolarisation allow for
Allows for compensatory movement
What impact does angular acceleration have
If we move the head, endolymph moves and displaces the cupula therefore helps displace hairs to cause depolarisation or hyperpolarisation to send info to the brainstem. Therefore the SSC are responsible for angular acceleration
What is the output signal from angular acceleration
Velocity from the vestibulocochlear nerve
How do SSC work in pairs?
According to the planes - when one side is stimulated the other is inhibited therefore the left anterior works with the right posterior as they are in the same plane
What is the VOR
Vestibulo - ocular reflex. Allows us to keep the image fixed during head movement in the retina
What is the VSR
Vestibulospinal reflex
Works when we are about to lose balance e.g. if we are walking we will get muscle relaxation or contraction to keep our posture
What neural connection does the VOR rely upon
Connection between vestibular nuclei and the oculomotor nuclei
What are the mechanics of the VOR
Eye movement occurs in the opposite direction to head movement, but it occurs at the same velocity and amplitude
What is the neural connection is the VSR dependent on
There is a motor connection to the limb muscles (lateral tract) and to the neck and back muscles (medial tract)
What are the mechanics of the VSR
Postural control by avoiding falls and compensatory body movement according to the head position
What does assessment of the vestibular system contain?
ACE VIPS
Anamnesis Posture and gait Cerebellar function Eye movement Vestibular tests Imaging (CT, MRI) Symptoms
What is anamnesis
History - some disorders are so specific that you can get a clear diagnosis straight away
What vestibular tests can we perform
Caloric test
Video head impulse test
Vestibular evoked myogenic potential
Rotational test
What is the caloric test
Stimulate the inner ear with different temperatures to generate nystagmus or dizziness - we are seeing if eye movement is symmetrical
What is the vHIT
Video head impulse test - tests both the vestibular organs and is generally tolerated well
What is the VEMP
Tests the neck muscles - if we get no neck response then we may have vestibular problems
What is the rotational test
Good but requires more equipment - char with rotary motor is used to see if we can generate a vestibular response
What are the main symptoms of balance disorders
Dizziness or vertigo - very common (occur in 25% of ENT and neurological referrals)
What is vertigo
Perception of rotation
What is dizziness
More vague than vertigo - related to vertigo but also may include blurry vision, nausea or general vertigo
Hoe can we categorise balance disorders
Location of the affected structure of the evolution of signs and symptoms
Where do peripheral vestibular disorders occur
Labyrinth and/or VIII nerve
Where do central vestibular disorders occur
CNS (brainstem or cerebellum)
What are examples of peripheral vestibular disorders
Vestibular neuritis
BPPV
Meniere’s
Unilateral and bilateral vestibular hypo-function
What is BBPV
Benign paroxysmal positional vertigo - the abnormal presence of otoliths in the canal
What is Meniere’s disease
Increase in liquid in the inner ear therefore the tympanic membrane breaks and we get cell intoxication
What are examples of central vestibular disorders
Stroke
MS
Tumours e.g. vestibular schwannoma
How do we classify ventricular disorders based on evolution
Acute
Intermittent
Recurrent
Progressive
What acute vestibular disorders can we get
Vestibular neuritis (labyrinthitis) Stroke
What intermittent vestibular disorders can we get
BPPV - comes and goes whenever someone moves their head
What recurrent vestibular disorders can we get
- Meniere’s (crisis = liquid ruptures membrane, but then the membrane can rebuilt in-between crises)
- Migraine (vestibular migraine)
What progressive vestibular disorders can we get
Schwannoma vestibular (VIIII nerve) Degerative condition e.g MS
What can be other reasons for dizziness aside form vestibular problems (7)
Heart disorders Presyncopal episodes Orthostatic hypotension Anaemia Hypoglycaemia Psychological Gait disorders
