otolithvestibular

Otolithvestibular refers to the otolith-vestibular sensory system within the inner ear, responsible for detecting linear acceleration and head position relative to gravity. The system consists of two otolith organs, the utricle and saccule, each containing a macula—the sensory epithelium—overlaid by a gelatinous otolithic membrane that contains otoconia, small calcium carbonate crystals. The otoconia increase the mass of the membrane, making it sensitive to static gravity and linear motion.

The utricular macula is oriented to sense horizontal accelerations and head tilt in the horizontal plane, while the saccular macula responds primarily to vertical accelerations. Hair cells extend into the otolithic membrane; displacement of the hair bundles by the weighted membrane deflects the stereocilia and kinocilium, producing receptor potentials and neurotransmitter release.

Signal from the hair cells travels via the vestibular nerve, a division of the vestibulocochlear nerve (CN VIII), to the vestibular nuclei in the brainstem and to the cerebellum and other centers. These signals help drive the vestibulo-ocular reflex to stabilize gaze, and the vestibulospinal pathways to maintain posture. They also contribute to perception of orientation and motion when integrated with visual and proprioceptive input.

Clinical relevance includes otolith dysfunction, which can cause imbalance, dizziness, or abnormal perception of verticality. Diagnostic tests such as vestibular-evoked myogenic potentials (VEMP) probe saccular and utricular function. Otolith involvement is also linked to conditions like benign paroxysmal positional vertigo (BPPV), where displaced otoconia may migrate into semicircular canals, producing vertigo with head movements. Management may include canalith repositioning maneuvers and balance rehabilitation.