Vestibular function Flashcards
What is the vestibular system + what does it consist of (3)
Found in the inner ear and is a series of fluid filled membranous tubes (labyrinths) which are embedded in the petrous part of the temporal bone
3 semi-circular canals, utricle and saccule
What is a utricle
swelling at the base of all 3 semicircular canals
What does the base of the collective 3 semicircular canals connect to
Utricle which then connects to the saccule
Semicircular canals are at what angle to each other
Right angle
What is the swelling at the base of each semi-circular canal called (NOT UTRICLE WHICH IS THE SWELLING AT THE BASE OF ALL 3 CANALS)
Ampulla
Inside the ampulla (swelling at the base of each individual semicircular canal) are sensory receptors called …
Cristae
Cristae (sensory receptors inside the ampulla) consist of a flexible gelatinous structure called the … which stretches across the entire width of the ampulla
Cupula
What does the cupula (flexible gelatinous structure inside the ampulla) respond to
Movement of endolymph in the semicircular canals
Embedded in the gelatinous cupula are … … … … … which synapse directly with the sensory neurons of the … …
cilia of sensory hair cells
vestibular nerve (vestibular branch of CN VIII)
Movement of endolymph in the semicircular canals pushes on the … therefore moving the … … … embedded within it
cupula
sensory hair cells
If head rotated left or right, endolymph in semicircular canals doesn’t move initially due to what
However, the … moves instantly
its inertia (tendency to remain unchanged)
ampulla
Inertia (tendency to remain unchanged) of endolymph causes what
Produces drag which bends the cupula and consequently the cilia embedded in it, in the opposite direction the head is moving
If you rotate at constant velocity, what does the endolymph do
However sudden stop in movement causes what effect with endolymph
Endolymph catches up following the initial inertia then rotates at the same speed as head movement
Endolymph still continues to move due to momentum creating a sense of movement and dizziness as eyes has told brain you’ve stopped moving but semicircular canals still tell brain you’re moving
2 types of cilia of sensory hair cells in the ampulla
Single large KINOCILIUM
Set of progressively smaller STEREOCILIA
Distortion of the cilia in the direction of the KINOCILIUM causes what to happen with regards to the vestibular nerve
DEPOLARISATION and increased discharge of APs in the vestibular nerve
Distortion of the cilia away from the KINOCILIUM causes what to happen with regards to the vestibular nerve
HYPERPOLARISATION and decreased discharge of APs in the vestibular nerve
Describe how hair cells in the cupola organs of the semicircular canals detect rotational acceleration (3)
Shearing forces act on cupula because of inertia of endolymph
Rotating at constant velocity so endolymph now rotating at same velocity as base, so no shearing forces
When rotation stops, momentum of endolymph causes shearing of cupula again but in the opposite direction to that at the start
What are the otolith organs (2)
Utricle
Saccule
What 2 other things contain sensory hair cells as well as the ampulla (swelling at base of each semicircular canal)
Utricle and saccule
The sensory component of semicircular canals is the ampulla, what is the equivalent for the utricle and saccule
Macula
Sensory hair cells in the macula eof the utricle/saccule detect … acceleration where the ampulla detects … acceleration
Linear, i.e. up/down/forward/back
Rotational
Sensory hair cells of the utricle detect what kind of acceleration
horizontal, i.e. head tilting forwards/backwards/walking
Sensory hair cells of the saccule detect what kind of acceleration
vertical, i.e. up/down a lift
The maculae of the utricle and saccule also have a set of cilia (one large kinocilium and a series of stereocilia like in the ampulla) which protrude into a gelatinous mass called the…
+ what is the equivalent of this in the ampulla
otolith membrane
cupula
Embedded in the otolith membrane (cilia in the maculae of the utricle and saccule protrude into this) are what
Otoliths (calcium carbonate crystals)
Otoliths (calcium carbonate crystals) embedded in the otolith membrane respond to what
gravitational pull
How do the hair cells in the otolith organs (utricle and saccule) detect linear acceleration
Movement causes the otoliths to move which distorts the otolith membrane and therefore moves the cilia that protrude into the membrane
Backward tilt of the head moves otoliths in the direction of what cilia
the kinocilium –> depolarisation and increased discharge of APs
Opposite for forward tilt
List the 3 major sensory inputs which contribute to the perception of our body space
- Projections from the vestibular nuclei on one side project ipsilaterally, bilaterally and contra-laterally to descending motor pathways
- Vestibular nuclei receive input from proprioceptors signalling limb and body position,
- Vestibular nuclei project via the thalamus to the cerebral cortex
What 2 tracts do the vestibular system reflexes involve
Vestibulocortical
Vestibulospinal
Name 3 vestibular system reflexes
1) TONIC LABYRINTHE REFLEXES
2) DYNAMIC RIGHTING REFLEXES
3) VESTIBULO-OCULAR REFLEXES
Describe what the tonic labyrinth reflex is (1) + how it works (1)
Keep the axis of the head in a constant relationship with the rest of the body.
Uses information from maculae and neck proprioceptors
Describe what the dynamic righting reflex is + what animal is it most profound in
Rapid postural adjustments that are made to stop you falling when you trip
Cats
Describe what the vestibulo-ocular reflex is
where activation of the vestibular system causes eye movement
A rotation of the head is detected, which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the muscles on the other side, thus preserving the image on the centre of the visual field
How is the vestibular system associated with eye movement in the vestibulo-ocular reflex (2)
Afferents (sensory fibres) from the semi-circular canals project and connect (within the vestibular nuclei) to afferent fibres travelling to the extraocular nuclei
visual system also sends powerful descending projections which control posture and vestibular apparatus, hence increased difficulty with balancing when you close your eyes
Name 2 vestibulo-ocular reflexes
Static reflex
Dynamic vestibular nystagmus
Describe the static reflex (a type of vestibulo-ocular reflex)
When you tilt head, eyes intort/extort to compensate so that over a certain range, the image stays the right way up
Describe dynamic vestibular nystagmus (a type of vestibulo-ocular reflex)
- what is it
- what restricts the reflex to keep occurring
A series of saccadic (rapid simultaneous) eye movements that rotate the eye against the direction of rotation of the head and body so that the original direction of gaze is preserved despite head rotating
The extent of eye movement is restricted; when eyeball comes to the end of its range of movement, it rapidly flicks back to the zero position i.e. straight ahead
In dynamic vestibular nystagmus (a type of vestibulo-ocular reflex), what is the direction of nystagmus
The direction of the rapid flick back, so right rotation of head –> right nystagmus (eyes rotate left as head rotates right then eye quickly flicks back right)
What tests can be used to test vestibular function (2)
Post-rotatory nystagmus
Caloric stimulation
Describe how a post-rotatory nystagmus test can be used to test vestibular function (2)
Subjects rotated in a chair, e.g. if rotated to the left then during acceleration should get a left nystagmus
At the end of rotational, for about 20 secs, during deceleration should get a right nystagmus due to endolymph catching up and rotating at same velocity so now pushing cupola in opposite direction
Describe how a caloric stimulation test can be used to test vestibular function (2)
Fluid is inserted into ear
- Warm fluid (44°C) causes nystagmus TOWARDS affected side, so warm fluid in R ear –> R nystagmus
- Cold fluid (30°C) causes nystagmus AWAY from affected side, so cold fluid in R ear –> L nystagmus
The caloric stimulation test is used to test which semi-circular canal
horizontal
Describe the COWS abbreviation for the caloric stimulation test (testing vestibular function)
Cold Opposite, Warm Same
- cold fluid causes nystagmus away from affected side
- warm fluid causes nystagmus towards affected side
Powerful maintained stimulation of the vestibular system can give rise to
kinetosis = motion sickness
Name 2 diseases that affect vestibular function
Labyrinthitis
Meniere’s disease
What is labyrinthitis
Acute interference with normal vestibular function as a result of infection, usually viral infection
Define vertigo
perception (hallucination) of movement in the absence of movement
Presentation of labyrinthitis (5)
Nausea/vomiting Vertigo - disabling Dizziness Hearing loss Nystagmus
What is meniere’s disease + presentation (4)
Episodic auditory and vestibular disease characterised by -sudden onset of vertigo, - hearing loss, -tinnitus, and -sensation of fullness in the affected ear
Meniere’s disease cause
Idiopathic but thought to be associated with over-production or impaired absorption of endolymph
List 3 damaging factors of vestibular function
Drugs - streptomycin
Chronic vestibular impairment
Brainstem lesion
What drug is the inner ear sensitive to
Streptomycin
If there’s chronic vestibular impairment, it can be compensated by what
visual system
