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Vertigo and Vestibular Disorders

Vestibular sensation is mediated by two relatively simple reflexes. The vestibulo-ocular reflex (VOR) ensures optimal visual processing during head motion by stabilizing the line of sight, also called gaze. The vestibulospinal reflexes (VSR) facilitate changes in antigravity muscles in order to help keep the head and body upright. There are two sensors within the vestibular labyrinth that respond to acceleration and thereby transduce the motion and the position of the head into peripheral and ultimately central biological signals.

These two sensors are the semicircular canals (SCC) and the otolith organs. The SCCs sense angular acceleration in order to process information concerning head rotation. The position of the cupula within the ampulla of the SCC can be translated into primary vestibular afferent information to encode head velocity. During angular head movement, endolymph within the SCC moves relative to the cupula, a membrane, which spans the canal. Processes of adjacent hair cells are displaced when the cupula is deflected, producing either depolarization or hyperpolarization, depending upon the direction of cupula movement.

In the case of eye movements, the goal of the VOR is to maintain visual fixation sufficient for foveation. The input for the compensatory slow phases of the angular VOR in response to head rotation is derived from information within the SCCs.

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Vertigo and Vestibular Disorders