Vestibular Physiology Flashcards
Balance involves the integration of what?
Vision; proprioception; vestibular system
What does the vestibular system sense?
note minor derangements can cause VERTIGO, disorientation, nausea
- Sense the dynamic and static position of the head by detecting linear and angular acceleration.
- Awareness of head position and reflex control of eye movements
What is vertigo?
Perception of motion, person or environment when there is no movement.
Differs to dizziness
Often associated with autonomic symptoms, sweating etc
Vestibular system inputs and outputs
Inputs: vestibular part of the 8th cranial nerve from the inner ear
Outputs: from the vestibular nuclei to cerebellum, eye, cortex, spinal cord
Structure/organisation of the vestibule
Three semicircular canals: Superior(ant): posterior: Lateral (horizontal)
In the central part the utricle (connected to canals) and saccule
What do the different parts of the vestibule sense?
Ampulla of semicircular canals: Contain the CRISTAE AMPULLARIS that sense angular acceleration
Utricle and saccule: contains the otolithic organs, the macula sacculus and utriculus that detect static head position and linear acceleration
Nerve supply of vestibule
Superior and inferior vestibular nerves in Scarpas ganglion exits as part of the vestibular part of CN8
Vestibular nerve divisions and what they innervate
Superior: utricle, ant saccule , horizontal and anterior semicircular canals
Inferior: post saccule and post semicircular canal
How are the canals paired? Important physiologically that they operate bilaterally in pairs
The lateral canals of both ear are paired
The anterior canal is paired with the posterior canal of the contralateral ear
Sensory cells in the vestibule
Similar to the cochlea in that there are hair cells with stereocilia, main difference is the presence of a large kinocilium. This determines the polarisation of the hair cell
Type 1 (calyx) and 2 hair cells
What is inside the cristae ampullaris
In the outer tube containing endolymph there is a swelling at one end. This contains the crista ampullaris, a piece of epithelial that extends into the tube, with the hair cells on it, with a layer of gel extending to the roof called the cupula.
Like a dam
What can be said about the hair cell orientation in the cirta ampullaris
They would all be polarised in the same direction, kinocilia all on the same side/plane along the length of the tube.
Otolithic organs cell arrangement in urticle and saccule
Hair cells are arranged on macula( utriculus and sacculus), stereocilia project into the otolithic/otoconial membrane which contains calcium carbonate crystals
How are the hair cells arranged in the vestibular organs?
All the hair cells are polarised and arranged to be in the same direction. In the canals, one direction. In the urticle, towards the midline (horizontal plane), the saccule away (vertical plane)
How are the hair cells stimulated?
A stimulus towards the kinocilium will depolarise the cell, a movement away will hyperpolarise the cell
How does the ampulla sense angular acceleration?
The hair cells are stuck in place whereas the fluid (endolymph) in the semicircular canals moves. When you rotate the fluid remains stationary for a moment, causing an apparent flow. This causes a deflection of the cupula and thus the stereocilia in the opposite direction.`
How are the otolithic organs (utricle and saccule) detect linear acceleration?
The maculae detect it due to the calcium carbonate in the otoconial membrane. Due to gravity, the mass of membrane, bending the hair cells.
Semicircular canal pairs and the sensory output. I.e a head movement in one direction ill do what to the pair?
aVOR
Moving the head one way will cause excitation on one side and inhibition on the other. The brain relies on the coupling to determine the direction of movement.
How does vertigo happen from a hair cell firing point of view?
Due to the fact the brain relies on inputs form both sides, if one side has a lesion, there is no input from that side, giving apparent movement at rest
VOR
clinical lecture? doesn’t explain well
