utriculi

Utriculus is one of the sensory components of the vertebrate inner ear, forming part of the vestibular system that detects motion and spatial orientation. The term utriculi is the Latin plural form used in scientific writing to refer to multiple utricular structures or, more broadly, to the utricle in a plural sense. In everyday English, the organ is usually called the utricle (plural utricles), while utriculi appears mainly in Latinized or taxonomic contexts.

Anatomically, the utricle is a membranous sac located in the vestibule of the inner ear, adjacent to the saccule and connected with the semicircular canals. Its sensory epithelium is the macula utriculi, which contains hair cells topped by a gelatinous otolithic membrane. The membrane bears otoconia, small calcium carbonate crystals, which shift with linear acceleration. Deflection of the hair bundles on the hair cells converts mechanical stimuli into neural signals that travel via the vestibular nerve to brainstem and cerebellar centers.

Physiologically, the utricle primarily senses linear acceleration and the head’s position relative to gravity, with the macula oriented to detect horizontal movements. Together with the saccule, which is more sensitive to vertical acceleration, the utricle contributes to the perception of tilt, motion, and balance.

Development and evolution: the utricular apparatus is present across jawed vertebrates, though its exact structure and orientation can vary among species. Clinically, dysfunction of the utricle or its pathways can contribute to vertigo and imbalance, and vestibular tests sometimes assess utricular function as part of a broader evaluation of balance.