Lecture 18 Flashcards
What is the point of the vestibular system?
Answers two basic questions: - "Which way is up?" - "Where am I going?" Contributes to - Keeping our eyes still as we move - Maintaining our upright posture - Our ability to perceive our own movement within space
What does the orolith organs control?
Linear motion
- forward or backward
What does the utricle sense?
Horizontal (feeling of acceleration in car)
What does the saccule sense?
Vertical (feeling of moving upward in elevator)
What does the semi-circular canals sense?
Head rotation
Horizontal (spinning)
Anterior vertical and posterior vertical act antagonistically to each other depending on the direction of rotation
What is the ampulla?
Sensory structures
Signals lead to vestibular nuclei in brain cell
What is the vestibular labyrinth filed with?
Endolymph
What are the hair cells of the vestibular system?
Sensory receptors of the vestibular system
- Found in all of ampulla, utricle and saccula
- Lip links causes opening of channel in hair bundles to let K in endolymph
- Same principle as hair cells of the auditory system but they respond to lower frequencies (0-20Hz)
How is the vestibular hair bundle structurally different from auditory hair cells?
Vestibular saccular hair cell
- vestibular hair cells keep their kinocilium throughout life
- Kinocilium is a true cilium unlike stereocilium
- Bundling of cilia make it better to transmit low frequency stimuli
What are the two types of vestibular hair cells?
saccule and utricle (detect head tilt and acceleration)
Where are hair cells found?
In a sensory patch called the macula
What do the hair cells project onto?
Gelatinous otolithic membrane
Which is denser, the otonocia or the gelatinous otolithic membrane?
otoconia
Does the otoconia respond to gravity differently from the gelatinous otolithic membrane?
yes
How does the otoconia move?
Moves downward and drags membrane and hair bundles down
- selective inhibition and activation of hair cells
How can the vestibular input to the CNS be ambiguous?
Information from the utricle and the saccule must be integrated with that from visual or somatosensory systems
How does gravity affect the vestibular system?
Otoconia and endolymph are heavier than hair bundles
- moves slower than the rest of the structure where hair cell body is
Endolymph and membrane moves to the left where hair cells move to the right
- confusion
- brain integrates information from different sensory paths
- tilt vs acceleration
What is the structure of the cupula?
Gelatinous structure penetrated by hair bundles
How does the ampulla control the direction of hair cells?
One side of ampulla makes hair cells orient in one direction while the other side makes them orient in the other direction
What does the semicircular canals detect?
Angular acceleration (rotation)
How does the semicircular detect rotation?
The inertia of endolymph during rotation displaces the cupula
Endolymph area slower to move than rest of head
How does alcohol cause the sensation of rotation?
- Hair cells on outside of semicircular canal is moving but the hair on the inside does not so it looks like they are moving in the opposite direction
- Cupula pushes hair bundles in one direction or another
- Alcohol absorbs into the cupula easily than the endolymph - causes spinning sensation when drunk
- Alcohol will disperse out of cupula and into endolymph - feels fine
- Next day - more alcohol in endolymph than cupula - spinning sensation in opposite direction
Important to drink plenty of water to dilute alcohol
How do the semicircular canals work?
In pairs on either side of the head
- Horizontal canals on both sides lie in roughly the same plane so can act as a functional pair
- The anterior canal on one side lies in parallel with the posterior canal on the other side so acts as a functional pair
What are the steps of the Vestibulo-ocular reflex?
- Shake your head while reading
- Shake the book you are reading from
- Which is easier?
What does the vestibular nystagmus allow?
Resetting of eye position during sustained head rotation
What happens when the subject is seated and rotated towards the right at a constant rate in the dark?
Slow phase: Eyes rotate in the opposite direction to head movement
Fast phase: Rapid resetting movement back to the center of the gaze
- Right quick phase movement = right beating nystagmus
How does eye flicking keep up with rotation?
Up - leftwards
Down - Rightwards
Rotating right - eyes move to the left
Slow phase and fast phase = nystagmus
“nod”
- stops after a while as endolymphs manage to catch up to the rotation
- Left quick phase movement = left beating nystagmus
What is Meniere’s Disease?
Poorly understood, spontaneous condition
- No definitive cause
- Potentially due to excessive endolymph
What are symptoms of Meniere’s Disease?
Intermittent, relapsing vertigo (spinning feeling)
- Vertigo happens with no apparent reason
- Vertigo can typically last 2-3 hours but in severe cases can last 2-3 days
- removal of vestibular system
Can be accompanied by tinnitus and distorted hearing
What are treatments for Meniere’s Disease?
diuretics, sedatives, steroids
Extreme treatment: remove the labyrinth or destroy vestibular hair cells
- Hair cell removal
- - aminoglycosides e.g. gentomyosin
- - -antibiotic
- - - prevents K from going into endolymph
- - - apply antibiotic to vestibular labyrinth
- - -risky as it can affect cochlea so concentration is important
