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Vestibular System

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University of Windsor
Biological Sciences

Outline of Lecture 41 (03-06 D; Minor) Vestibular System I. Function and properties of vestibular system - The function of the vestibular system is to sense and control motion - Vestibular afferents from the bony labyrinth project to vestibular nuclei (brainstem) - Vestibular nerve has superior division (to horiz., sup. semicircular canals and utricule) and inferior division (post. semicircular canal, saccule) - The semicircular canals respond to angular acceleration whereas the otoliths (saccule and utricle) respond to linear acceleration and translational movement of the head - The membranous canal is filled with endolymph (high K) and the other vestibular space is filled with perilymph (high Na), which sets up electrochemical gradient needed for signaling - Mechanical deformation of stereocilia to or away from kinocilium excites and inhibits hair cell activity, respectively - In semicircular canals, physical movement of endolymph against cupula causes deformation; all of the hair cells are oriented identically - In otolith, hair cells project into mass containing CaCO 3rystals (otoconia), which transduces linear acceleration into shear force across hair cells; the hair cells are oriented in opposite directions II. Vestibular reflexes - Vestibulocollic (VCR) reflex stabilizes the head; vestibuloocular (VOR) reflex stabilizes the eye - Reflex pathway is a three neuron arc: vestibular nerve afferent  central vestibular neurons  extraocular neurons (III, VI)  eye muscles; cerebellum provides conscious control at level of central vestibular neurons - Reflex pathway has appropriate excitatory and inhibitory syn
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