vestibular system Flashcards
what is the role of the vestibular system
- what type of sensation is it
- what reflexes are evoked
- it isint a conscious sensation
- Reflexes evoked
– Equilibrium and balance
– Stabilization of visual field
what are the 2 sub organs of the vestibular system
- semicurcular canals
- otolith ( macular) organs
what is included withing the semicircular canals
- Sense angular acceleration ( turning head/body)
– Inertial mechanism
– Rapidly adapting (phasic) receptors (pacininan corpuscles)
what is included in the otolith ( macular) organs
- Sense linear acceleration and static position of head
– Gravitational mechanism
– Slowly adapting (tonic) receptors
structure of the semicircular canals
- The canals are oriented in X, Y, and Z planes. Aka horizontal, anterior vertical, and
posterior vertical canal. - Each canal has an expansion of the canal called the ampulla
- ( canals are tilted in the head)
what is the semicircular canal structure
- Filled with endolymph
- Ampulla
– Crista ampullaris
– Hair cells - synapse with afferent fibers of the vestibular branch
– Cupula (watertight seal)
what is found on the hair cells
- have cilia
- kinocillium (tller)
- steriocilia ( smaller
charecteristincs of hair cells
- 1 kinocilium
- 100 stereocilia
- Synaptic vesicles
what happens when the the cilia are depolarized and hyperpolarized
-Depolarization:
- If the cilia are bent towards the kinocilium, you get depolarization and release of
transmitter
Hyperpolarization:
- if cilia are bent in the opposite direction, you get a hyperpolarization and reduces the release of transmitter from the hair cell
hair cells have ____ firing rate
high
what is the mechanism ehrn kinocilium is pulled away from the sterocilia
If the kinocilium
pulls away from the sterocilia (as seen above), the mechanically gated channels open up, allowing
K+ to flow in
- depolarization
- Ca2+ flows in
- synaptic vesicles release transmitter into
synaptic cleft
- activation of afferent nerve (CN VIII)
Vestibular afferents
- what branch is it
- where are the cell bodies
- what is the firing rate
- Vestibular branch of CN VIII
- Cell bodies in vestibular (Scarpa’s)
ganglion - Have high resting firing rate (60 spikes/sec)
How do semicircular canals convey information about turning of the head?
- if the canal is moved to the right
- endolymph has inertia and moves in the opposite direction ( statys put) and the cupula is pushed in that direction and so is the kinocilium
orientation of steriocilia - horizonatal canal
If the person moves their head to the right, the endolymph on both canals will move towards the
left.
- In the right ear, the kinocilium is bent left, and will open the sterocilia channels right ear
gets excitation
- In the left ear, the kinocilium is bent left, and will close the stereocilia channels left ear gets
inhibited
in the vestibular system youll get paired ______ signals
what does this mean
- opposing
-so you’ll get excitation in one ear
and inhibition in the other ear.
note: each semicircular canal transduces _____ velocity in plane of duct
angular
Note:
no signal if movement is normal ___ ____ __ ___
to plane of duct
NOte:
if rotation is at angle to plane of duct ___ ___ ___ ___ ___
signal is vector fraction
what is the structure of the otolith organs ( within the vestbule of the ear)
- Macula is a patch of hair cells
- Covered by gelatinous mass
- Otoconia embedded in mass
- Otoconia are CaCO3
crystals
orientation of otolith organs
- where are the organs located
- what is the orientation
- Otolith organs are located in saccule and
utricle - Utricular macula is horizontal
- Saccular macula is vertical
what forces act on otoconia
- what do these movements cause
- Shearing forces act on otoconia
- Otoconial movements cause stereocilia to
be deflected
what occurs to the cilia in the forward tilt of the head
When the man tilts his head down, the horizontal macula is tilted, and gravity acts on the cilia.
This causes the cilia to be deflected downwards.
how are shearing forces produced
- Linear acceleration or deceleration
- Tilting of head
reflexes evoked by the vestibular stimulation
- maintainve of equilibrium
- stabalization of the visual fied
maintenance of equilibrium afferent fibers connect to ?
– Lateral vestibulospinal tract (extensor muscles)
stablizationof visual orientation afferent fibers connect to ?
- medial longitudnal fascicules
what does the medial longitudnal fascicules connect
occulomotor nuclei and vestibular nuclei
where do vestibular afferents terminate in
– Vestibular nuclei
– Cerebellum ( direct input to the cerebellum)
what are the vestibular nuclei
- which cranial nerve goes to these
Lateral, Inferior, Medial, and Superior vestibular nuclei
- CN VIII goes to all 4
Vestibualr nuclei - efferents
- To abducens, trochlear, oculomotor nuclei (via
ascending MLF) - To neck motor neurons (via descending MLF)
- To limb and trunk motor neurons (via LVST)
- To cerebellum
- To reticular formation
- To VPM and cerebral cortex
what happens if you have loss of vestibular function
- Difficulty maintaining balance
- Visual disturbances while walking
- Nystagmus (ossicaltion of the eyes)
- Vertigo
- Nausea
what are the vestibular system disorders
- Benign positional vertigo
- Meniere’s disease
- Acoustic neuroma
- Ototoxic drugs
- Trauma
what occurs during motion sickness
Occurs when motion signals transmitted by eyes,
vestibular system and proprioceptors are at variance with
one another or with what is expected from previous
experience.
what are the symptoms of motion sickness
Evokes autonomic reactions (nausea, vomiting, pallor,
sweating, hypersalivation, stomach awareness) and
drowsiness and fatigue.
what happens if you have contibued exposure to motion sickness
- Continued exposure leads to disappearance of the reactions
what is the theory of motion sickness
- “Sensory conflict and neural mismatch” theory”
