4 - the vestibular system lecture Flashcards
what does the vestibular system detect and act as?
detects forces generated by movement, acting as an accelerometer
the vestibular system translates the forces detected into a sense of what?
balance
what does the vestibular system provide information about?
the position of the head in space
what effect does the vestibular system have on other CNS structures?
allows other CNS structures (eg. brainstem, cerebellum, basal ganglia etc) to rapidly compensate for changes
what is the vestibular system embedded in?
bone (bony/membranous labyrinth)
where is the vestibule located?
between the semi-circular canals and the cochlea
semi-circular canals vs vestibule
semi-circular canals — balance with MOVEMENT
utricle and saccule — STATIC balance forces
the vestibule contains the ____ and ____ which have equilibrium receptors called ____?
- utricle and saccule
- maculae
describe the saccule
- continuous with the cochlear duct anteriorly
- vertical acceleration (lift)
describe the utricle
- continuous with the semi-circular ducts posteriorly
- horizontal acceleration (car)
what do the semi-circular canals form and detect?
- form the dynamic system
-detect angular acceleration
what do otolith organs form and detect?
- form the static system
- detect linear acceleration
what are the otolith organs?
utricle and saccule
what are otoconia?
- calcium carbonate crystals
- form the striola which in turn rests on the otolithic membrane
- give weight
what do otolith organs detect?
changes in linear acceleration
what layer are the hair cells embedded in?
gelatinous layer
describe the unstable system of the otolith organs
- otoconia give weight — wobbly
- sensitive to changes in acceleration
- move to bend hair cells
- depolarisation or hyperpolarisation
what are macula?
equilibrium receptors
what is endolymph high in?
K+
where is endolymph?
in the semi-circular canals/ducts
where does signal transduction occur in the semi-circular canals?
in the ampullae (at the base of the canals)
what are the semi-circular canals sensitive to and what is this essential for?
pitch, roll and yaw — essential for coordination of eye movement
what semi-circular canals are there?
horizontal, superior and posterior
the movement of what fluid has an effect in the vestibular system?
endolymph
the movement of endolymph has what effect?
- displaces a gelatinous mass known as the CUPULA
- this causes a physical strain on HAIR CELLS
- the displacement of cells due to the sloshing of endolymph causes either depolarisation or hyperpolarisation
> lots of hair cells project into the jelly-like cupula
deflection towards vs. away from the kinocilium
towards = increases firing
away = decreasing firing
what do semi-circular canals allow for?
very rapid detection of changes in angular acceleration of the head
what kind of transmission is used in the semi-circular canals?
glutamatergic
what does the vestibulo-ocular reflex prevent?
retinal slip
describe the vestibule-ocular reflex
- head rotates left, eyes rotate right
- left eye: contracts medial rectus, relaxes lateral rectus
- right eye : contract lateral rectus, relaxes medial rectus
what is Scarpa’s ganglion?
- aka. vestibular ganglion
- in internal auditory meatus
- ganglion of the vestibular nerve
describe the vestibular pathway from the vestibular ganglion
signals travel throguh the vestibular portion of CN VIII into the vestibular nuclei in the brainstem. the vestibular nuclei send projections into the cerebellum, spinal cord, thalamus and nuclei of the oculomotor (III), trochlear (IV) and abducens (VI) nerves
what are slow vs fast phase movements triggered by?
slow — mediated by vestibulo-ocular pathway
fast — triggered by cerebral cortex
how can nystagmus be clinically tested?
- by introducing warm or cold water into the external auditory meatus
- causes convention currents in the endolymph — stimulates hair cells as if the head was rotating leading to nystagmus
- slow phase is still present in a comatose patient, but not the fast phase (as this is controlled by cortex)
what does a dysfunctional slow phase imply?
a lesion in the vestibulo-ocular pathway
describe the vestibulo-spinal tract
- basic balance and postural control
- axons from vestibular nuclei descend ipsilaterally
- synapse on LMNs
- activity in the vestibular nuclei is modulated in the cerebellum
what is Ménière’s disease?
- vestibular dysfunction
- increase in endolymph pressure
- disrupts signal transduction and can result in tinnitus, nausea, spontaneous nystagmus (by stimulating these reflexes)
what is benign paroxysmal positional vertigo (BPPV)?
- vestibular dysfunction
- dislodged bits of otolith stimulate the cupula in the posterior SSC causing vertigo
what manoeuvre attempts to nudge the dislodged bits back to the vestibule in BPPV to remove nausea and dizziness?
the Epley manoeuvre
when does motion sickness occur? treatment?
when there is a mismatch between data from different sensory modalities and with what the rest of the brain expects to happen (eg. on plane, vestibular system says you’re moving, vision and proprioception says you’re staying still)
treat with antihistamines, look at horizon (to match vestibular and visual systems)
