vestibular system Flashcards
What are the canals in the bony labyrinth?
semicriculat canals, vestibules, and cochlea. The canal connecting to the outside is vestibular aqueduct.
What are the membranous labyrinth?
semicircular duct, utricle + saccule, and cochlear duct. The vestibular aqueduct is filled with endolymphatic duct and sac.
What filled the membranous labyrinth?
Endolymph
Where is the endolymph made?
strae vescularsi in teh cochlea
How is endolymph different from other fluid (perilymph, CSF)?
Lots more K; +80mV compared to perilymph
What is the gradient between the hair cell and the endolymph?
endolymph +, hair cell is negatively charged.
How are the two K flows?
- Rapid K in flow from endolymph
- Passtive K outflow at base of harid cells into perilymph - rapid repolarization
What happens when vibration/mechanical force opens the K channel on tip of the stereocilia?
K channal opens and K flushes in, causing the hair cell to depolarize
-however these K is leaky, constitutively open
What are the Ca channels at the base of the hair cells?
- There is voltage-dependent Ca channel, which allows Ca to come in during deplorization - help with vesicle’s release of neurotransmisstor
- Ca also helps an Ca-dependent K channel, which allows K to go out.
Which direction the stereocilia needs to bend in order to fire AP?
Towards the kilocilium -> tension on the tip filament -> K in -> depolarization
What does tip links connect to?
Anchor in K channel, the other on a transmembrane motor protein on the side of neiboring steoreocilium (motor protein walks along actin filament)
Where are the hair cells?
- macula (applied to the wall)
- utricle
- saccula
What is macula?
- exists in utricule and sacculus
- Hair cells attached to the wall embedded ina gel
- the gal has otolith -calcium carbonate cystals, which increases the density of the gel - alooing the macular to respond to gravity.
- hari cells are polarized in different directison depending on their locations (striola)
Where is crtistae located?
- located in ampulla of semicircular duct
- all hair cells signal in one direction
What is the function of the maccula?
Detect linear acceleration and position in relation to gravity.
Benign positional vertigo
-caused by loose otoconia
Why difficult to know the direction during diving? Or pilot lost tract of gravity when flying through a cloud
- when the visual information conflicts with vestibular, we often use visual information.
- slow movement are easily adapted
When head tilt how the AP changes?
One direction - AP increases frequency;
another direction -decreases discharge rate
What about Christae?
- located in the ampula of semicircular ducts
- the cilia protrudes into the tall cubula.
- kilocilium is on the same side of the hair cells.
What does Christae detect?
- There are three, perpendicular to each other
- detecting the angular acceleration.
- think about fluid in the holu loop, inertia.
What about the orientation of the three canals?
- one canal in each ear is parallel to the other ear
- names: L and R - horizontal, anterior, and posterior
If head tilt to one direction, what happens next?
- Endolymph moves to the other direction -> cupula displacement in the ampula
- increasing firing on one side and decreasing firing on the other side (each of the inner ear can complete the task)
What is the semicircular canal’s innervation?
Terminal branches of the vestibular branch of CN VIII. Each maculae and christae has one branch innervating.
What is the ganglion located at the end of internal acoustic meatus?
vestbular ganglion (Scarpa’s ganglion), where the cell bodies are, are sensory neurons: bipolar in this case
Where is the first order neuron projecting to?
vestibular nuclei and to the flocculus and nodulus (vestibulocerebellum)
Where is the fibers from cristaae going to?
lateral, medial and superior vestibular nuclei
Where is the vestibular trigone?
Lateral to the sulcus limitans; very lateral in the brainstem (sensory!)
Where do the vestibular nuclei receive input besides direct vestibular input?
- cerebellum: mostl the flocculus and gastigial nucleus
- Spinal cord: incorporating proprioception from the body (esp from the upper neck)
What does the input of the cerebellum do with the vestibular system?
- Adjust the gain of the vestibular system
- Reciprocal connections with the flocculonodular lobe of the cerebellum
- These connections are critical to the ability to change gain of the VOR and adaptation of vestibular responses.
Motion sickness
-adjusted by the cerebellum - adaptation
What is the most important output for vestibular information?
- adjusting the eye movement via the vestibulo-ocular reflex
- projection through MLF, connects to nuclei (e.g. abducent, oculomotor)
- stabilize the eye on the target when head is moving
What underlines the vestibulocervical and vestibulospinal (righting) reflexes?
projection from medial and lateral vestobular nuclei to spinal cord (e.g. holding a baby in hand -> title towards the other side -> baby’s extensor muscles on the turning side will be activated to trying to maintaining the balance (in adult, this primitive reflex is suppressed)
What carries the vestibular information?
Thalamocortical pathway
What is the physiological nastagmus?
- Head rotates to one side - imbalance of input on two sides
- fast eye movement: vestibular-ocular reflex, drives the eye opposite to the direction of head movement
- slow eye movement: cerebral cortex detects and moves a new direction, so it can regain a visual input “I have to see something”.
How does the spotting help with readjustment?
suppress the cerebral reaction; hope the vestibular-oculo gets used to quickly
What is caused by spontanous nastagmus?
Imbalance of vestibular system (maybe damage)
What is caloric testing?
- Injecting ice water into the ear, cold water dense and sinks -> test the vestibular organs in each ear separately.
- warm water in fluid rising -> convection current in another direction, feeling like moving, eye will drift (nastagmus)
- for someone in a coma, test if brain stem is damaged.
- In clinical setting, use body-temp water to clean!!!
