Physiology-Vestibular System Flashcards
What types of movements are sensed by the vestibular system?
Angular acceleration and linear acceleration (includes gravity)
Movement in which direction will cause depolarization of the kinocilia and stereo cilia seen below?
Bending of hairs towards kinocilium produces depolarization and increased NT release. Bending away from the kinocilium causes hyperpolarization and decreased NT release. Perpendicular bending does not cause any change because the stereo cilia are not linked in that direction.
What regions of the ear are responsible for sensing linear acceleration?
Utricle (linear) and saccule (vertical). Note the striola have hair cells facing in different directions, this allows for sensing movements in all different directions.
What structures make the gelatinous layer dense enough for the hair cells to be able to sense changes in acceleration?
Otoliths.
Why is the vestibular system relevant to pilots taking off from aircraft carriers?
The rapid acceleration causes the gelatinous layer to bend toward the kinocilium. This creates a feeling that you are traveling upwards, when you’re really not that can last for 30 seconds. Pilots need to be aware of this so they don’t put the nose of the plane down and crash it.
What structures of the ear are used in detection of angular rotation?
Semicircular ducts (all 6 pairs!): Left & Right: anterior, lateral & posterior.
How does the ampulla of the semicircular ducts differ from the utricle & saccule?
In the ampulla, the cupula is the gelatinous layer w/o otoliths. In the ampulla all hair cell axis are aligned w/o striola.
How does your brain use the left lateral semicircular duct to communicate the angular acceleration seen below?
As the head rotates, the fluid in the cupula lags, bending the stereo cilia. This causes hyperpolarization of hair cells in the crista ampullaris, decreased NT release and decreased signal firing from the cochlear nerve.
How does your brain receive information from the left and right lateral semicircular ducts when the head rotates as shown below?
Rotation of the head to the left causes displacement of the cupula towards the kinocilium in the left lateral duct and away from the kinocilium in the right lateral duct. This causes depolarization in the left lateral duct and hyperpolarization in the right lateral duct.
Why do semicircular ducts not respond to linear acceleration?
Movement of cupula on each side balances out.
Why do you get tipsy when you are drunk?
Alcohol makes the cupula less dense than the corresponding fluid on the other side. This gives a sense of rotation when you accelerate linearly.
During normal physiologic conditions (not in an airplane) what signal is perceived by the CNS from vestibular nerve firings? What about when you are on an airplane? Why is this a problem?
The firing rates are proportional to angular velocity. Under non-physiologic conditions they are proportional to angular acceleration, however, the CNS still interprets the information as velocity.
Vestibulo-ocular reflex.
Smooth: eyes rotate slowly opposite in the direction of head motion. Saccade (nystagmus): eyes rapidly fix on a new point to gaze on and rotate in the direction the head is rotating.
You spin around really fast to the right and stop. Which way will you have nystagmus while you are spinning and when you stop?
When you start spinning to the right, the right vestibular nerve depolarizes and the left hyperpolarizes. This causes a right nystagmus. When you stop spinning, the fluid continues to move and bends the cupula the other direction, causing a sense of leftward rotation., The left is depolarized and the right hyperpolarized. This causes a left nystagmus (shown below).
What happens to nystagmus if you keep spinning at the same velocity for 45 seconds?
Nystagmus goes away because acceleration is gone and the cupula is no longer pushed one way or another and neither nerve is stimulated.
What is the ascending pathway of nerve stimulation by the vestibular nerves?
Utricle, saccule or semicircular duct -> vestibular (Scarpa’s) ganglion -> axons form vestibular nerve -> cerebellopontine angle -> vestibular nuclei (4 shown below)
Purpose of this tract
It originates from the lateral vestibular nucleus and projects to all ipsilateral levels of the spinal cord. It excites alpha motor neurons of the upper and lower limb extensors in response to vestibular nerve stimuli (righting reflex).
Purpose of this tract.
It originates from the medial vestibular nucleus and goes bilaterally down the cervical spinal cord in the MLF. This helps control and stabilize movements of the neck and head.
A 60 year old female comes to see you complaining of dizziness when she sits up from lying down and sometimes feels like the world is spinning around her when she is stationary. Physical exam reveals left nystagmus when she rotates her head left. How do you treat her?
She has benign paroxysmal positional vertigo. A loose otolith landed in the cupula and changed the density of it. This causes her to feel like she is spinning when she’s actually doing nothing. You need to do a number of jerky head maneuvers to dislodge to otolith from the cupula to relive her symptoms.
