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Flashcards in Vestibular system Deck (35)
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How is angular (rotation) detected?

Semicircular canals


How is acceleration, strength and static position of the head detected?

Otolith organs


List some functions of the vestibular system

Subserve proprioception of movement
Provides reflex balance reactions i.e. vestibulospinal reflexes
Provides stability of eye during head movements i.e. vestibulo-ocular reflexes
Assists in controlling HR and BP during fast head tilts
Provokes motion sickness in abnormal movements
Creates a perception of spatial orientation


List some disorders of the vestibular system

Vestibular ataxia
Vestibular nystagmus
Slight loss of orthostatic control in acute phase
Severe nausea and vomiting in unilateral vestibular loss
Unable to coordinate
Oversensitive to visual motion


Where is the vestibular apparatus located and what type of fluid lies in the membranous tubes?

In the petrous part of the temporal bone


What are the otolith organs called?

Utricle and saccule


Where are the hair cells located and what are the three layers that comprise this area?

The maculae
STATOCONIA, hair tufts, hair cell layer


How do the otolith organs detect the stimulus of linear acceleration?

The endolymph in the utricle or saccule will move when acceleration occurs
Statoconia will move as well and will bend the hair cells underneath in the direction of gravitational pull
Otolith hair cells are directed by deflection forces to inertial resistance to acceleration


What does statoconia comprise of and why is this important?

Calcium carbonate crystals and matrix which is 2-3 times the specific gravity of the endolymph so it's weight can bend the ciliary projections of the hair cells


How does the vestibular nerve come into play with the otolith organs?

The nerve fibres at the base of the maculae join to form the sensory vestibular nerve along with cell bodies in the vestibular ganglion


How is upward/downard head movement detected?

Hair cells in the maculae of the saccule project horizontally (overall vertical orientation) to detect vertical motion


How is side-to-side head movement detected?

Hair cells in the maculae of the utricle project vertically (overall horizontal orientation) and can detect lateral and anteroom-posterior movements


What are the names of the semicircular canals?



What is the name of the sensory component in the semicircular canals?

Crista ampullaris


What are the components of the sensory organ in the semicircular canals?

Hair cells project hair tufts which are attached to a gelatinous mass called the CUPULLA.
Nerve cells lie underneath the hair cells.


How is angular rotation detected in the semicircular canals?

Endolymph moves when the head does (inertial influence)
Causes the cupula to move in the same direction
This pulls the hair cells underneath and causes and electrical signal to be sent down the vestibular nerve
[Stimulated due to endolymphatic rotation]


What is the difference in stimulation of the semicircular canals compared to the otolith organs?

When direction is in a certain direction, the direction preferentially stimulates the canals on that side.
This is because the hair cells are unidirectionally orientated.


What happens in the semicircular canals when acceleration stops?

The canal on the opposite side is stimulated and the other is inhibited.


What happens at rest in the semicircular canals?

There is a tonic firing rate produced so that the tonuses of each canal balance out.


What happens if there is loss of canal function on one side?

There will be permanent/partial loss of stimulation in the 'on' direction for that canal.


What are the components of the cilia?

On the apical membrane of the hair cell are stereocilia and one kinocilium (detects movement), connected by tip links.


Describe the process of depolarisation of the hair cells in the maculae and cupula

When the stereo cilia move in the direction of the kinocilium, K+ channels open
Influx of K+ from potassium rich endolymph
Causes depolarisation
The hair cells travel via a synapse with the primary neurone dendrite to the vestibular ganglion to send a signal
Movement in the opposite direction of the kinocilium causes hyperpolarisation


Describe the vestibular pathway

Afferent fibres travel to the vestibular ganglion -> CNVIII -> vestibular nuclei (superior, lateral , medial, inferior) -> project to;
Spinal cord
Nuclei of extraocular muscles
Thalamus (VL and VM)
Autonomic centres


Describe the path of the vestibulospinal tract

Otolith organs contribute to the vestibulospinal tract off the cerebellum.


Describe the path of the vestibulospinal tract

Otolith organs contribute to the vestibulospinal tract off the cerebellum.
Lateral vestibulospinal; descends ipsilateral in the ventral funinculus and terminates in the lateral ventral horn. Influences limbs e.g. extensor antigravity muscles

Medial vestibulospinal; descends bilaterally in the medial longitudinal fasiculus to the cervical and upper thoracic spine -> stabilise neck and back


Where does the information from the semicircular canals go to?

Travels up via the medial longitudinal fasiculus and contributes to stabilising eye movements


What contributes to postural reflexes?

Sensory info from the vestibular apparatus, somatic receptors and eyes help change muscle tone, mediated by the vestibulospinal and rubrospinal tracts -> fibres sent to the flocculonodualr lobe.

Cerebellar efferents from the fastigial nucleus to the vestibular apparatus contributes to posture movements.


Describe the vestibular-ocular reflex

1. Axons of the medial vestibular nucleus cross the midline and supply CNVI to adduct the eye
2. Other axons from the CNVI nuclei travel to the contralateral CNVIII via MLF to adduct the other eye via the medial rectus
3. Axons of the superior vestibular nucleus in vertical canals travel ipsilaterally to innervate CNIII and CNIV to generate vertical vestibulear-ocular reflexes


What is the cause of vertigo?

Vestibular nuclei project to the thalamus to the tempo-parietal cortex for proprioception.
In unilateral lesion canal lesion, the onus of the intact canal indicates that the head is rotating to that side.
The patient may feel a spinning motion as a result.


Why does vestibular nystagmus present and how?

Acute unilateral canal lesion; tonus in the intact canal is unopposed and the eye slowly moves towards the lesion (as if the head was turning to the opposite side).
The brainstem detects this and moves the eye back to the intact side.
'Slow drift away from lesion, fast saccade towards the lesion'.