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Semicircular Canals
- 3 each and oriented at 90degrees to each other, pair of canals for each plane
- provide info about rotational movement of the head; roatation, side to side, up and down
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Canal's fluid
filled with endolymph
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Cupula
- hair cells which bend in response to endolymph movement
- when bent, hair cells lead to action potentials which are carried over vestibular divisions of cranial nerve VIII into the brain stem
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Otolith Organs: Saccule and Utricle
- each have specialized receptor area called macule
- weight of otoconia bends the hair cells to signal linear motion and info regarding head position to nucleus
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Macule
has specialized hair cells upon which is a gelatinous matrix with otoconia (ear rocks) embedded in it
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3 Main Functions of the Central Vestibular System
- Gaze Stabilization
- postural stability
- spacial orentations
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Gaze Stablilization
as we move our heads, reflexes occur automatically which keep visual images in the fovea. Called VOR
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Medial Vestibularspinal tract
influences head control
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Lateral Vestibularospinal Tract
goes to proxminal extensor muscles
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Spatial Orientation
info goes to cortex for conscious awareness of orientation of body and head in space
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Other outputs from the vestibular system to infulence level of arousal
- info from vestibular nucleus also goes to the reticular activating system
- ex. rocking chair relaxing
- shaking head to wake up
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info from the vestibular nucleus also influences ANS and can lead to
- nausea and vomiting
- these symptoms often are present in a vestibular pathology
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Dizziness
- not exact term
- means feeling a tendency to fall
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Vertigo
- illusion of movement, usually of spinning
- occurs most often with Acute Unliateral Peripheral Vestibular pathology
- results bc brain cant make snese of the disrupted input
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Lightheadedness
feeling about ready to faint
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Dysequilibrium
feeling unsteady or off balance
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Benign Paroxysmal Positional Vertigo BPPV
caused by the otoconia being displaced into the SSC
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Unilateral Vestibular Hypofunction UVH
caused by pathology in peripheral vestibular system on one side
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Bilateral Vestibular Hypofunction BVH
caused by pathology in peripheral vestibular system on both sides
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Bening Paroxysmal Positional Vertigo
- most common peripheral vestibular pathology
- hallmark is vertigo onset with certain positions
- sudden vertigo occurs because the otoconia dislogde from the utricle and saccule, migrate into the SCC and in certain postions cause bending of the hair cells
- short lasting
- tx is manuvers to reposition the otoconia back into the otoliths
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UVH causes
viral infections, vascular events, trauma
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UVH Presentation
there is usually rapid onset of vertigo, spontaneous nystagmus, postural instability, dysequilibrium
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