09 16 2014 Vestibular System Flashcards
Vestibular system tasks?
- controls reflexive eye movements
- cerebellum and oculomotor nuclei - Vestibulo-ocular reflexes keep the eyes still when the head moves
- vestibulospinal reflexes : enable the skeletomotor system to compensate for head movements
Symptoms of vestibular system disease?
Vertigo vs. dizziness (with feeling of the world spinning)
Nauseau, vomiting, pallor, perspiration
Difficulty walking
Sensation of spinning or rhythmic movements
Nystagmus (jerky eye movements
Oscillopsia
vestibular damage that makes it difficult or impossible to fixate on visual targets while head is moving.
-feel like the words is spinning around you
Blood supply to labyrinth?
What would happen if there is a stroke in this area?
AICA
-sudden hearing loss and vertigo
Semicircular canals
- angular acceleration : rotation
- functions in paris with opposite canal on opposite ear
- hair cells are in ampulla. Hair cells in ampule are covered by a gelatinous mass called a CUPULA.
- Cupula has weight and when head moves it lags behind and bends hair cells
Direction of hair cells in Semicircular canals
Anteriror : Facing up and away from utricle
Horizontal: slightly down and towards utricle.
Posterior: Horizontal
Utricle
-what is in it?
Macula: thick sensory epithelium with hair cells oriented in the horizontal plane.
Also has otoconia (calcium carbonate crystals) embedded in otolithi membrane
-displacement = action potential
Saccule
Macula: thickened epithelium with hairs oriented in the vertical plane
-responds to linear acceleration in vertical plane.
Movement that Saccule and Utricle comprehend?
Linear acceleration of head (in any direction) AND static head position
Striola
utricle and saccular areas are divided by a striola– just an area that divides hair population having opposite polarities
BPPV?
Benign Paroxysmal positional vertigo
- otoconia detaches from otolithic membrane of the utricle and it gets stuck in the semicircular canal.
- obstruct flow of cupula
Usually unilateral but can sometimes be bilateral
Lateral vestibular nucleus controls what?
posture, vestibulo-spinal reflexes
medial and superior vestibular nuclei control what?
vestibulo-ocular reflexes; vestibulo-cervical reflexes
Inferior vestibular nucleus does what?
integration of inputs from the vestibular labyrinth and the cerebellum
Medial and superior vestibular nuclei innervation?
- receives fibers predominantly from the semicircular canals
- efferents include MLF, oculomotor nuclei, and cuddly to spinal cord
-Medial vestibular nuclues –> medial vestibular tract = vestibulo-cervical reflexes.
Medial nucleus efferents are excitatory
Superior nucleus efferents are inhibitory
Lateral vestibular nucleus innervation?
aka Deiter’s nucleus
-Afferents from semicircular canals and otolithic organs.
Efferents mostly to the lateral spinovestibular tract.
Largely conceded with postural control
Inferior (descending) vestibular nucleus innervation?
What is this nucleus mostly concerned with?
Afferents from otolithic organs and cerebella cortex (purkinje cells)
Efferents mostly to cerebellum and reticular formation, contralateral vestibular nuclei and spinal cord.
Concerned with integrating central motor signals with vestibular input
Lateral vestibulospinal tract
Ipsilateral
Principal pathway by which otolithic organs can regulate bodies extensor organs
major source: LVN
minor contributor: SpVN
Medial Vestibulospinal tract
Bilateral
projects through MLF
Major source: MVN
Mainly cervical
Vestibulo-cervical reflexes
Vestibulothalamic projections
ascending pathway (poorly understood)
- Ventroposterolateral (VPL), pars oralis
- Bilateral projections
- tend to arise from the medial vestibular nucleus.
Other targets are VP, VL, and intralaminar nuclei.
Nystagmus
typical to side contralateral to the dysfunction of vestibular apparatus
involuntary rhythmic movements of the eyes consisting of a rapid movement in one direction and a slow movement in the opposite direction
Caloric test
irrigating the external auditory meatus with warm or cold water.
Nystagmus towards warm water and away from cold water.
Optikinetic Nystagmus
fast component in the opposite direction to that of the moving lines
-ex. looking at telephone poles while in passenger seat in car
Vestibular-occular-reflex (VOR)
particular system that produces eye movements that counter movements of head
-permit gaze to remain fixed on a particular point.
Vertigo vs. dizziness
vertigo– spinning sensation of movement
Dizziness: light headedness, nausea, unsteadiness on one’s feet
vestibular neuritis
inflammation of vestibular ganglia or fever due to a viral infection or idiopathic inflammation
acoustic neuroma
cerebellopontine angle tumors
onset: 50 yrs of age
Occurs at the point where CN 8 enters the internal auditory meatus.
-early symptom: tinnitus (unilateral) and unsteadiness
positional testing
helps identify BPPV of any of the semicircular canals and other causes for positional dizziness
central vs. peripheral vertigo
and nystagmus
Peripheral lesions: delay of 2- 5 secs before the onset of nystagmus and vertigo.
- horizontal or rotational
- fades within 30 secs
- fades with adaptation to tests
Central lesions: nystagmus and vertigo begin immediately and there is no adaptation.
- horizontal or rotary nystagmus
- Vertical nystagmus, nystagmus that changes directions while remaining in the same position, nystagmus in the absence of vertigo is ONLY CENTRAL.
Gaze nystagmus
have patient gaze no more than 30 degrees from front. If there is a problem, the nystagmus is contralateral to the dysfunctional side
Positional nystagmus
nystagmus is induced by particular head positions. These patients are particularly troubled by vertigo
can the vestibular system adapt?
Yes
-astronaut – goes to space (no gravity) comes back to earth (gravity)
