Model of Phase-pposition Activation of Vestibular Hair Cells

DING Dalian; QI Weidong; Richard Salvi

doi:10.3969/j.issn.1672-2922.2017.06.021

Abstract：The vestibular sense organs contain two different types of sensory hair cells,type I and type II,that dif-fer in the length of the stereocilia,shape of the cell body and their afferent and efferent synapses and nerve endings.The kinocilium and stereocilia of vestibular sensory hair cells are embedded into the otolithic membrane on the macula of saccule and utricle and the hair cells in the semicircular canal are inserted into the cupula overlying the cristae.When the otolithic membrane or cupula are displaced due to gravity or motion-induced inertial fluid flow,bending in the direc-tion of the tallest cilia causes hair cell depolarization while bending toward the shortest cilia causes hair cell hyperpolar-ization,changes that lead to excitation or inhibition of the afferent vestibular neurons respectively.The hair cells in the macula of the saccule and utricle are divided into two areas by the striola,which curves through the middle of macula.Hair cells in the utricle are oriented with their kinocilium facing the striola,whereas hair cells in the saccule are oriented with their kinocilium facing away from the striola.Therefore,the polarity of the hair cells on opposite sides of the strio-la of the macula of the utricle and saccule are activated in phase opposition.When the body accelerates along a plane perpendicular to the striola of the macula,the hair cells on one side of striola will be excited(depolarized)whereas those on the other side will be inhibited(hyperpolarized).The polarity of the hair cells in the three ampulla have stereocilia oriented in the same direction.The tallest stereocilia on hair cells in the lateral semicircular canal are oriented toward the utricle,whereas those in the superior and posterior canal are oriented away from utricle.The crista of ampulla is sad-dle-shaped and the cupula covering the crista extends to the opposite wall of the ampulla.When the overlying cupula is displaced by the flow of endolymph,the stereocilia of the hair cells on one side of the saddle-shaped crista will be de-flected toward in the direction of the crest.However,we speculate that the stereocilia on hair cells on the opposite of the crest of the crista will be deflected in the opposite direction due to fluid turbulence and backflow towards the crest of the crista.In this model,the hair cells on opposite sides of the cupula in the semicircular canals also respond in phase op-position,similar to that seen in the macula.