Vestibular System Flashcards
List the 3 main inputs the vestibular system includes.
Visual, proprioceptive and vestibular information
What are the outputs of the vestibular system?
Reflexes to maintain a stable posture and stable gaze.
OCULAR REFLEX and POSTURAL CONTROL
Which nervous system integrates the inputs of the vestibular system and generate the outputs?
CNS
Where does the vestibular organ reside?
Within the posterior area of the inner ear
The ear is separated into 3 parts. Name them.
Outer, middle and inner ear
What type of cells are present in the inner ear for hearing and balance?
Hair cells
What structure within the inner ear is anterior?
The cochlea concerned with auditory input.
What structure within the inner ear is posterior?
Labyrinth concerned with the vestibular system. The bony labyrinth resides within the petrous part of the temporal bone.
Where are the utricle and saccule located and what are they joined by?
The utricle and saccule are located within the vestibule and are joined by a conduit. (saccule is also joined to the cochlea)
How many semicircular canals are there in each ear?
Anterior, posterior and lateral
What are the ampullae of the semi-circular canals on each side connected to?
Utricle
What is the labyrinth in the skull?
Superior projection located within the petrous part of the temporal lobe.
The location of the vestibular organ draws planes for what?
Anterior and posterior canals.
These planes determine which structure will be stimulated with a specific head movement.
Name the 2 main structures that hair cells in the vestibular system have.
Vestibular hair cells have a kinocilium (largest cilium) and stereocilia.
What is the purpose of cilia in vestibular hair cells?
Cilia allows the cells to depolarise the cell with movement of the endolymph generated by head movement.
What are the otolith organs?
Utricle and saccule
Where are the cells of the otolith organs located?
On the maculae, placed horizontally in the utricle and vertically in the saccule.
What do the maculae contain?
The maculae contain the hair cells, a gelatinous matrix which includes otolith crystals superiorly located (carbonate crystals that support the deflection of stereocilia).
Where are the hair cells of the semicircular canals located?
Ampulla
What does the rest of the semicircular canal (not the ampulla) have?
The rest of the canal only has a liquid high in potassium called endolymph.
What does the ampulla of the semicircular canals have where the hair cells are located?
Crista
What are the hair cells present in the ampulla surrounded by?
Cupula which helps the hair cell movement.
Should otoliths be present in the semi-circular canals?
No
The orientation of the canals in the head defines 3 planes. List them.
Anterior and posterior canals form a 90 degree angle. Lateral canals are horizontal to the other canals.
Where do primary afferents of the vestibular nerve end?
Vestibular nuclei and cerebellum
Where do vestibular nuclei have projections to?
SC, nuclei of the extraocular muscles, cerebellum and centres of cardiovascular and respiratory control.
The main processing centres of the vestibular cortex reside where?
Within the parietal lobe, in the parieto- insular vestibular cortex (PIVC).
Does one specific area contribute to the vestibular cortex?
Not one specific area since many inputs and integrators are involved, many cortical areas participate.
What does the central processing part of vestibular physiology involve?
The central processing involves the vestibular nuclear complex (primary processor) and the adaptive processer, the cerebellum.
List 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.
Hair cell potentials
Hair cells have a resting potential, the basal discharge of the nerve; upon head movement, there is subsequent depolarisation of the hair cells due to endolymph movement within the crista.
What does hairs moving toward the kinocilium generate and how does it affect nerve discharge?
Hairs moving towards the kinocilium generates depolarisation and increase in nerve discharge.
What does hairs moving away from the kinocilium generate and how does it effect nerve discharge?
Hairs moving away from the kinocilium generates hyperpolarisation and a reduction in nerve discharge.
Describe the relationship between the left and right ear.
There is an antagonistic relationship between the left & right ear (excitation and inhibition simultaneously occur at that specific velocity).
What do otolith organs detect?
Detects linear acceleration and tilt (otolith movement).
What do otolith organs detect?
Detects linear acceleration and tilt (otolith movement).
What detects head tilt: backwards and forwards and what detects no head tilt: acceleration and deceleration?
Head tilt: Backwards and forwards - Saccule = vertical movement.
No head tilt: Acceleration and deceleration - Utricle = horizontal movement
How is angular acceleration detected?
Angular acceleration is detected due to endolymph movement within the cupula (displaces hair cells). This is transmitted to the brainstem whereby the output signal is through the vestibulocochlear nerve (detected as velocity).
What is the output signal on the 8th CN?
Velocity
Semicircular canals work in pairs according to what?
According to their planes.
E.g. both laterals; anterior from one side with posterior of the opposite side.
What is the vestibular-ocular reflex?
Reflex ensuring images remain fixed within the retina. This involves a connection between vestibular nuclei and oculomotor nuclei.
Eye movement in opposite direction to head movement (with same velocity and amplitude).
What is the vestibulo-spinal reflex (VSR)?
This concerns motor neurones to limb muscles (lateral corticospinal tract). The contraction of muscles is dependent on head movement.
Motor neurones to neck and back muscles (medial tract). Postural control, there is compensatory body movement according to the head position.
Outline the assessment of the vestibular system.
Anamnesis (History): Disorders are specific with patient history in order to determine the specific cause of the pathology.
Posture & gait: Can be determined by Posturography.
Cerebellar function: Using imaging (CT scan & MRI)
Eye movements: This can be examined during consultation.
List the vestibular tests that can be done as part of the assessment of the vestibular system.
Caloric test (Stimulates the inner ear with different temperatures to identify how symmetric the responses are – it is a test of the lateral semi-circular canals)
Video head impulse test (vHIT): Measures the Vestibulo-ocular reflex.
Vestibular evoked myogenic potential (VEMP)
Rotational test
What are the 2 main symptoms of balance disorders?
Dizziness
Vertigo
How can balance disorders be categorised?
Based on the location of the affected structure and evolution of signs and symptoms.
What is the location of central vestibular disorder as opposed to peripheral vestibular disorders?
Central vestibular disorders - CNS (brainstem/cerebellum)
Peripheral vestibular disorders - Labyrinth and/or VIII nerve
List examples of peripheral and central vestibular disorders.
Peripheral vestibular disorders - Stroke, MS, tumours
Central vestibular disorders - Vestibular neuritis, Benign Paroxysmal Positional Vertigo (BPPV), Meniere’s disease, unilateral and bilateral vestibular hypofunction.
List the 4 different types of evolution of balance disorders and give examples of each.
Acute - vestibular neuritis, stroke
Recurrent - Meniere’s disease, migraine
Progressive - Schwanomma vestibular (VIIIth nerve), degenerative conditions (MS)
Intermittent - BPPV
List the differential diagnoses for dizziness.
Heart disorders Presyncopal episodes Orthostatic hypotension Anaemia Hypoglycaemia Psychological Gait disorders
