Glossary of SFS - Vestibular System

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How are the semicircular canals oriented? What are the 3 canals? What do they sense?
orthogonally (right angles). Horizontal, superior/anterior, posterior.
Head rotations and respond to angular accelerations.
Specialized for horizontal linear accelerations
Specialized for vertical linear accelerations
1. Head around vertical axis.
2. Axis of head nodding yes.
3. Around axis used to laterally bend head.
1. Yaw.
2. Pitch
3. Roll
Generates compensatory eye movements in resonse to head movements
Vestibulo-ocular reflex. Have to go over 2 Hz to lose ability to stay focused.
Provides a compensatory mechanism with a very short latency.
Vestibular system. Visual system has a much slower latency.
Maintain head position despite body movements
Vestibulo-colic reflexes
Helps maintain our posture if we start to fall over. Most important system for balance. Sends signals mainly to extensor muscles.
Major players in vestibular system (just like auditory)
Hair cells
When stereocilia move in direction of the kinocilium, what will happen? What about the opposite direction?
It will cause stretch and potassium will flow into the hair cell.
Opposite direction - potassium stops flowing.
Swelling at base of each semicircular canal?
In the ampulla, how are the stereocilia oriented?
In a single direction to sense canal rotation. Cilia are connected to a cupula to catch the endolymph as it moves.
Dividing component of sacculus and utricle.
Signaling in sacculus and utricle.
Push-pull. Orientation casuses signals to stimulate one group and oppose the other.
1. Maximal sensitivity in the sacculus.
2. Maximal sensitivity in the utricle.
1. Vertical linear acceleration.
2. Linear accelerations in the horizontal plane.
Calcium carbonate crystals and where they reside.
Otoconia. Reside in the macula.
Two things that can activate the hair cells via otoconia in the sacculus and utricle.
Static tilt and rapid acceleration.
Both cause hairs to bend. Vestibular system can actually get confused between the two and give the same signal.
How does the body tell the difference between tilt and acceleration?
Short, transient effect interpreted more as acceleration while a sustained effect is interpreted as tilt.
The hair cells in the sacculus, utricle, and semicircular canals respond to acceleration or deceleration via a __________ relationship.
Stimulating in one direction will increase the firing from the tonic firing already occuring, while stimulation in the opposite direction will cause a decrease in firing rate.
In the SC, hair cells send their stereocilia up into what?
cupula (spreads across ampulla)
Rotation of the head causes fluids within the SC to move and exert force on the cupula. This causes what to be deflected?
The stereocilia. Causing an increase/decrease in firing of the vestibular nerve.
Tilt head to what to isolate the horizontal canal?
30 degrees downward. Also brings utricles into horizontal plane and sacculus into the vertical plane.
Right anterior canal is paired in parallel plane with which canal?
Left posterior
Left anterior canal is paired in parallel plane with which canal?
Right posterior
Canal pairs point ____ degrees in their respective direction.
Within the pairs, moving in a direction will _________ firing in one, and ________ firing from the other.
Increase, decrease. Stupid question, I know.
SCs respond to _______, while the signals from the vestibular nerve are related to __________.
angular acceleration, head velocity
Net effect of turning your head on the semicircular canal system.
The cupula is moved, causing the vestibular nerve to send a signal to brain related to head velocity.
Why is it important that vestibular nerve records signals related to head velocity?
To use head velocity to control eye velocity.
Very rapid response, so that despite head moving left/right or up/down, your eyes can stay fixed on an object of interest.
Vestibulo-ocular reflex.
Caused when vestibular system is in conflict with the visual system.
In the VOR, signals come in from vestibular nerve and go where?
To medial vestibular nucleus
If head rotates left, signals from the left MVN make _________ connections on the contralateral abducens nucleus and via the MLF make _________ connections on the left oculomotor nucleus.
excitatory, excitatory
When head rotates left, the left MVN makes _________ connections on the ipsilateral abducens nucleus and via MLF contralateral oculomotor (right) nucleus
Goal of VOR.
Eyes move in opposite direction of the head at an appropriate velocity.
Causes ocular nystagmus and dizziness due to the VOR.
IF you continue to spin slowly at a constant speed, the fluid in the SCs won't be accelerating and the cupula will return to its natural position. When you stop spinning, the fluid decelerates moving the cupula.
VOR handles high frequency stimulation well, but has problems with what?
slow, continuous stimluations
Primarily influenced by the otolith, utricle, and sacculus. Involved with body tilting and preventing falling over.
Lateral vestibulospinal tracts
In response to body tiliting there will be activation of what motor neurons?
If you transect above the level of the vestibular nuclei, you will observe what type of rigidity?
Decerebrate rigidity in which all extensors of the limmbs are activated to prevent you from falling.
Primarily modulate head position. Vestibulo-colic reflex.
Medial vestibulospinal tracts. Example is dozing off and waking in class (signal to neck muscles).
Does the vestibular system degenerate over time?
YES. Elderly are more reliant on visual cues for balance, and have more problems with falls.
Cells in the lateral and superior vestibular nuclei relay where? Where do they project after that?
Thalamus (VPL). Vestibular cortex (ex. Area 3a - primary sensory cortex, parietal cortex)
What area of the cortex involved in the vestibular system helps you remember where other objects are located in relation to your body in space.
Parietal cortex
Eye movements allowing you to:
1. Look back and forth between tow stationary points.
2. Track a moving object
3. Look at objects at different distances.
1. rapid seccadic eye movements
2. smooth pursuit
3. vergence

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