GA: Vestibular System Flashcards
The vestibular system is essential for producing what?
Motor responses necessary for daily function
The vestibular system is divided into 5 components. What does the peripheral receptor apparatus do?
They are in the inner ear and transduce head motion/position
The peripheral receptor apparatus, central vestibular nuclei, vestibuloocular network, vestibulospinal network, and vestibulothalamocortical network all makeup what?
The vestibular system
What do the central vestibular nuclei do?
They are in the brainstem and control motor activites + spatial orientation
What does the vestibuloocular network do?
Eye movements
Allows you to keep a fixed gaze on an object while the head is moving (ex. reading a sign while driving)
What does the vestibulospinal network do?
Coordinates head movements, axial musculature, + postural reflexes
What does the vestibulothalamocortical network do?
Conscious perception of movement/spatial orientation
What is your vestibular system?
The vestibular system is a collection of structures in your inner ear that provides you with your sense of balance and an awareness of your spatial orientation,meaning a sense of whether you are right-side up or upside-down.
The vestibular labryinth is made up of?
Bony labyrinth (perilymph ~ CSF)
Membranous labyrinth (endolymph)
Semicircular canals measure what type of movement?
Rotational head mvmt (angular acceleration)
Otolith organs (utricle, saccule) measure what type of movement?
Translational head movements (linear acceleration)
Receptor cells in vestibular organs are innervated by what afferent fibers?
Afferent fibers of the vestibular ganglion (Scarpa ganglion)
What is the blood supply to the vestibular system?
Labryinthine A.
Stylomastoid A. (semicircular canals)
If you have an interruption of the labyrinthine A. this will cause what?
Vertigo
Nystagmus
(mess up vestibular + cochlear function)
What are some components in the membranous labyrinth?
Ampulla (the end of ducts)
Utricle + Saccule
Ductus reuniens (connects saccule to cochlea)
Endolymphatic duct (drains sinus)
What causes Meniere’s Disease?
The endolymph volume is messed up –> causing endolymphatic hydrops (abnormal distention of membranous labyrinth)
What are the symptoms of Meniere’s Disease?
Hearing loss, Vertigo, Tinnitus, Vomitting/Nausea
How do you treat Meniere’s Disease?
Diuretic + salt resticted diet to reduce the endolymphatic hydrops
(might put a shunt in)
What are the vestibular sensory receptors?
Hair cells w/ stereocilia + kinocilium
Type 1 hair cell =
nerve calyx
(central)
Type 2 hair cell =
Cilinder + innervated by synaptic boutans
(peripheral)
Where are crista + sensory receptors located?
In the ampulla
(where each duct ends in a prominent enlargement)
How does the ampulla (semicircular canals) work?
Rotational head mvmts produce angular accelerations –> endolymph displaced –> pushes cupula to one side or another –> displaces stereocilia in same directions
What is found in the macula (utricle + saccule)?
Otolith membrane (hair cells entend into)
Calcium carbonate crystals (otoconia)
How does the macula work?
Changes in head postion relative to gravity/linear accelerations displace otoconia, which bends underlying hair cell stereocilia
Where are the vestibular nuclei located?
*process postionsal + mvmt info for control of visual + postural reflexes
superior = pons
medial = 4th ventricle
inferior = medulla
What is the only snesory organ in the body that sends direct primary afferent projections to the cerebellar cortex + nuclei?
Cerebellum
What type of fibers go through the juxtaresiform body (inferior cerebellar peduncle)?
Primary vestibulocerebellar fibers
(send collaterals to the dentate nucleus and terminate as mossy fibers)
Secondary vestibulocerebellar projections are what?
When vestibular nuclei send fibers to fastigal + dentate nuclei
Vestibulvestibular fibers come from?
Vestibular nuclei
Spinovestibular fibers come from?
SC
How are you able to read a sign on a building while walking down the street?
Vestibuloocular reflex (stabilizing eye mvmts)
How would you describe the vestibuloocular reflex?
Compensatory
(eye muscles must be controoled in unison – horizontal)
How does the rotational (horizontal) vestibuloocular reflex occur?
Head looks one way & eyes look opposite
- MLF –> cont. abducens nucleus
- Abducens–> Ipsi. lateral rectus M.
- Abducens –> cont. oculomotor nucleus (medial rectus)
Example of leftward head turn:
(Horizontal/Rotational Vestibuloocular Reflex)
- Left horizontal semicircular canal activates neurons in left vestibular nuclei
- Commissural neurons decrease inhibition signals from right vestibular nuclei
- Neurons in left vestibular nuclei excite contralateral abducens motor neurons
- Produces contraction in right lateral rectus + left medial rectus
- Compensatory rightward eye mvmt keeps the object of interest on the fovea
What is nystagmus?
Combination of slow phases punctuated by fast return phases
What do you use to test patients complaining of dizziness or vertigo in the vestibular labyrinth?
The caloric test
(put warm + cold water into external auditory canal)
What is the COWS finding of the caloric test for the membranous labyrinth?
Cold water = nystagmus beating to Opp. side
Warm water = nystagmus beating to Same side
*this = a normal finding of the vestibuloocular reflex
The lateral and medial vestibulospinal tracts are part of what?
Vestibulospinal network
In the lateral vestibulospinal tract (postural control), where do these neurons go?
anterorostral areas:
posterocaudal areas:
anterorostral –> cervical cord
Posterocaudal –> lumbosacral cord
What is the function of the medial vestibulospinal tract?
Stabilizes neck
The vestibular thalamus gets information for spatial orientation –> so they need proprioception. Meaning they have nuclei where?
VPL + VPI
What do areas 2v + 3a do in the vestibular cortex?
Primary somatosensory cortex
What is area 7 of the vestibular cortex?
Parietal cortex –> spatial awareness
A lesion of the PIVS (Insular areas of lateral sulcus + parietoinsular vestibular cortex) does what?
Vertigo, unsteadiness
What does the prefrontal cortex + superior frontal gyrus control?
Frontal eye field + smooth pursuit eye mvmts
How would you describe dizziness?
Nonspecific
Spatial disorientation, nausea
How would you describe vertigo?
Can be specific/nonspecific
An illusion of body motion (spinning)
Roller coaster
What is benign paroxysmal postional vertigo?
Brief epidoes of vertigo that correspond w/ changes in body position.
What causes benign paroxysmal postitional vertigo?
Cupulolithiasis
Otoconial crystals from utricle separate from otolith membrane + become lodges in cupula of semicircular canal
A benign tumor that originates from Schwann cells of the vestibular root =
Vestibular Schwanoma
Vestibular Neuritis is thought to result from?
edema of the vestibular nerve (maybe from viral infection – herpes)
-severe vertigo, nausea, vomiting, but NO hearing loss
