Vestibular Flashcards
Proper balance requires…
Functional vestibular, proprioceptive and visual systems to be present, but only 2 of the 3 are essential for balance.
Vestibular system technically only is able to sense…
What your head is doing. For example, you can shake your foot in all directions and not get dizzy. Try that with your head and you will get very dizzy.
Where is the vestibular system located?
In the petrous portion of the temporal bone.
3 main parts of vestibular system and their functions
(1) SEMICIRCULAR CANALS- anterior, posterior and horizontal- good for precise head position!!!- full of fluid
(2) UTRICLE- connects 3 semicircular canals (otolithic membrane)- Primary gravity and Horizontal Acceleration sensor-calcium carbonate crystals
(3) SACCULE- continuous with cochlea- (otolithic membrane)- Vertical acceleration- calcium carbonate crystals
Ganglion which are associated with vestibular nerve
Scarpa’s ganglion
Where do the hair cells sit in vestibular system?
The ampulla of the semicircular canals, with their hairs sticking up in the path of the fluid. The hair cells are covered with gelatinous covering called the cupola. This area is referred to collectively as the CRISTA AMPULLARIS.
Inertial displacement
Quick movement will cause fluid to be displaced and lag behind, pushing on the Cupola (causing depolarization of hair cells)
These are ACCELERATION FORCES not velocity!
One side will depolarize and the other will hyperpolarize. The larger the acceleration, the largest the difference in hair cell movement, the greater the perceived movement.
Pairing of the semicircular canals.
The anterior canal on the right is paired with the posterior canal on the left and vice versa.
The horizontal canals are paired as well.
Hair cells are ______ active.
Tonically
The bipolar neuron always has a subtle output going to the CNS, but as long as they are the same on both sides, your brain interprets it as no movement– they cancel each other out.
How is the cupola over the saccule and utricle different from the cupola over the hair cells of the semicircular canals?
They have otolithic granules which push down and move the hair cells. The interpretation of this sense is a LEARNED entity, as you learn about where your body is in space.
This allows them to respond to gravity.
Path for vestibular input to CNS
(1) Hair cell
(2) Bipolar cell (action potential)
(3) Vestibular ganglion
(4) CN VIII
(5) Vestibular nuclei
4 divisions of the Vestibular nuclei
LATERAL- utricle and saccule- postural control of extensor muscles
MEDIAL and SUPERIOR- SSC and some utricle/saccule- ocular reflexes and coordination of neck and eye muscles
INFERIOR (DESCENDING)- all areas- goes to cerebellum and coordinates movement/balance
Function of ascending fibers (MLF)
Control eye movements
Function of descending fibers (MLF)
Control head and neck movements
Primary “concern” of Floccularnodular lobe
Vestibular information– where is the body in space
Purpose Indirect vs. Direct vestibular input
DIRECT: Immediate needs/ responses
INDIRECT: Pattern type movements
Where does vestibular output go after leaving the cerebellum?
It is projected back to the vestibular nuclei, to control limbs and movements.
Lateral Vestibulospinal Tract
- From lateral vestibular nucleus
- Uncrossed
- Entire cord length
- Proximal limb muscles
- Maintains balance by acting on the limbs
Medial Vestibulospinal Tract
-From the medial vestibular nucleus
-Bilateral projection (somewhat)
-Cervical spinal cord only
-Neck muscles
Maintains head erect
Dorsal columns vs spinal thalamic tract in terms of how many things they interact with on the way to the VPL
Dorsal columns head straight to VPL (on a mission), whereas spinal thalamic tract relays information to a bunch of locations (gossipy)
Main 5 eye-movements
- Vestibulo-ocular reflex (addition of warm or cold water causes eye movement)
- Optokinetic response (when head is moved, so are eyes)
- Smooth pursuit
- Saccadic eye movement
- Vergence eye movement
Nystagmus
Back and forth rhythmic movement of eyes. Usually slow (smooth) in one eye, and fast (saccadic) in the other.
Can clinically test via injection cold or warm water (COWS- Cold opposite, Warm same.) Cold water-eye moves quickly in opposite direction [example cold water in right ear, eyes move quickly to left, slowly to right]. Warm water does the opposite.
Where does dizziness come from?
Simply a mismatch or disconnect between the 3 systems which are needed for balance.
Explain vestibule-ocular reflex
During rotation of the head and faster than visual tracking, the VOR stabilizes the image on the retina.
As the head rotates, the VOR rotates the eyes with the same speed but in the opposite direction, thus keeping the image from “smearing” on the retina.
