VESTIBULAR SYSTEM Flashcards
What are the 3 main inputs of the vestibular system?
Visual, proprioceptive and vestibular (rotation and gravity) information
What are the outputs of the vestibular system?
Mainly reflexes to maintain a stable posture and stable gaze
Where is the vestibular organ located?
Posterior area of the inner ear called the labyrinth
Describe the structure of the vestibular organ
Utricle and saccule located in vestibule and joined together by conduit. Saccule also joined to cochlea by conduit.
Each ear also has 3 semicircular canals which have an ampulla on one side and are connected to the utricle
What are the 3 semi-circular canals called?
Anterior semi-circular canal
Lateral semi-circular canal
Posterior semi-circular canal
How is the labyrinth positioned in the skull?
Superior projection on base of skull
How is specific head movement distinguished by the vestibular organ?
The orientation of the semi-circular canals draws planes. A movement in each plane will stimulate the structures giving a map of how the head is moving.
The utricle, saccule and the 3 semi-circular canals gives 5 structures which work independently
What is the largest cilium on vestibular hair cells called?
Kinocilium
How is movement of the head sensed?
Movement of head causes movement of endolymph which shifts the hair cell’s cilia. The bigger the movement the bigger the depolarisation/hyperpolarisation
If stereocilia move towards the kinocilium the cell depolarises and vice versa.
Which organs of the vestibular organ are otolith organs?
Utricle and saccule
What are otoliths and what do they do?
Calcium carbonate crystals located on top of hair cells and gelatinous matrix. They help to deflect the hairs by adding weight
What does the maculae contain and where is it located?
Contains the hair cells, a gelatinous matrix and otoliths on top.
Horizontal in the utricle and vertical in the saccule
Where are the hair cells in the semi-circular canals located?
Ampulla - rest of the canal only has endolymph
Describe the structure of the ampullas
Hair cells located in the crista.
Cells surrounded by the cupula.
One end of ampulla leads to semi-circular canal and other end to the utricle
What sit the cupula?
Gel like substance surrounding the hair cells of the ampulla (canals) which helps with hair cell movement
Describe the planes formed by the canals
Anterior and posterior canals/planes form a 90 degree angle with the lateral canal/plane horizontal to them
Where do primary vestibular afferents from hair cells end/lead to?
Vestibular nuclei in the brainstem
Cerebellum for coordination and feedback
Where does the vestibular nuclei project to?
Spinal cord
Nuclei of the extraocular muscles (eye movement)
Cerebellum
Centres of cardiovascular + respiratory control
Where is the vestibular cortex located?
Not one specific area since many inputs and integrators involved spread over many cortical areas
What/where is the main processing centre of the vestibular system located?
Parietal lobe, in the Parieto-Insular Vestibular Cortex (PIVC)
What are then 3 functions of the vestibular system?
Detect and inform about head movements
Keep images fixed in retina during head movements
Postural control
How does the head know if it is not moving?
Hair cells have resting potential which gives a basal discharge to the nerve
What causes otolith movement?
Linear acceleration and tilt
What type of movement is the utricle sensitive to?
Horizontal movement e.g. travelator
maculae is horizontal
What type of movement is the saccule sensitive to?
Vertical movement e.g. lift
maculae is vertical
What are the semi-circular canals sensitive to?
Angular acceleration e.g. rotating head
Cupulla moves and displaces hair cells
What is the output signal on CN VIII (vestibulocochlear)?
Velocity
How are the semicircular canals/planes paired?
Horizontal canals on either side
Posterior on one side and anterior on the other
Anterior on one side and posterior on the other
How do the semi-circular canal/planes pairs work?
When one side is excited, the other is inhibited
How does the vestibulo-ocular reflex (VOR) work and its function?
Keeps images fixed in retina through connection between vestibular nuclei and oculomotor nuclei
Eye movement in opposite direction to head movement but same velocity and amplitude
How does the vestibulo spinal reflex (VSR) work and its function?
Motor neurons to limb muscles (lateral tract)
Motor neurons to neck and back muscles (medial tract)
Postural control, avoidance of falls and compensatory body movement according to head position
List the things you can assess for the vestibular system
Anamnesis (history)
Posture and gait
Cerebellar function
Eye movements
List the tests that can be carried out to investigate a patient’s vestibular system
Caloric test
Video head impulse test (vHIT)
Vestibular evoked myogenic potential (VEMP)
Rotational test
What is the caloric test?
Stimulate inner ear with different temperatures to generate eye movement. Allows for the test of vestibular organs independently
What is the vestibular evoked myogenic potential (VEMP)?
See if neck muscles have response if vestibular organ is stimulated
What imaging can you carry out to investigate a patient’s vestibular system?
CT, MRI
What are the symptoms of balance disorder?
Dizziness, vertigo
What is the difference between dizziness and vertigo?
Dizziness is the feeling of light-headedness, unbalanced or wooziness. Vertigo is a specific form of dizziness where you experience spinning sensation
What are the two types of balance/vestibular disorders based off location and what is affected?
Peripheral vestibular disorders (labyrinth, CN VIII)
Central vestibular disorders (CNS e.g. brainstem/cerebellum)
Which location of balance/vestibular disorders is more common and easier to manage?
Peripheral vestibular disorders
List examples of peripheral vestibular disorders
Vestibular nephritis
Benign paroxysmal positional vertigo (BPPV)
Meniere’s disease
Unilateral/bilateral vestibular hypofunction
What is benign paroxysmal positional vertigo (BPPV)?
Otoliths in the ampulla of semi-circular canals causing exaggerated movement of cupula
What is meniere’s disease?
Problem with the absorption of endolymph causing fluid build-up in inner ear which breaks the membrane
List examples of central vestibular disorders
Stroke
Multiple sclerosis
Tumours
What are the acute causes of balance/vestibular disorder?
Vestibular neuritis
Stroke
What are the intermittent causes of balance/vestibular disorder?
BPPV - only occurs when head is moved
What are the recurrent causes of balance/vestibular disorder?
Meniere’s disease - membrane regenerates and cycle continues
Migraine
What are the progressive causes of balance/vestibular disorder?
Schwannoma vestibular (CN VIII) Degenerative conditions e.g. MS
What could dizziness also be a sign of?
Heart disorders Presyncopal episodes Orthostatic hypotension Anaemia Hypoglycaemia Psychological Gait disorders
List the different vestibular nuclei
Superior
Lateral
Medial
Inferior
What nuclei does the vestibulospinal reflexes arise from and what is it’s function?
Lateral, medial and inferior vestibular nuclei
Posture
What nuclei do vestibulocerebellar reflexes arise from and what is it’s function?
Superior, lateral, medial and inferior vestibular nuclei
Coordination monitoring
What nuclei does the vestibulo-ocular reflex originate from and what is it’s function?
Superior, lateral, medial and inferior vestibular nuclei
Eye and head movement
