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The utricle, or utriculus ((ラテン語:utriculus), diminutive of ''uter'', meaning "leather bag"), along with the saccule, is one of the two otolith organs located in the vertebrate inner ear. The utricle and the saccule are parts of the balancing apparatus (membranous labyrinth) located within the vestibule of the bony labyrinth (small oval chamber).〔Moores, Kieth L. "Essential Clinical Anatomy" Lippincott Williams & Wilkins; Second Edition (2002).〕 These use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear accelerations and head-tilts in the horizontal plane. ==Structure== The utricle is larger than the saccule and is of an oblong form, compressed transversely, and occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it. The macula utricle is a thickening in the wall of the utricle where the epithelium contains vestibular hair cells that allows a person to perceive changes in longitudinal acceleration as well as effects of gravity. The gelatinous layer and the statoconia together are referred to as the otolithic membrane, where the tips of the stereocilia and kinocilium are embedded. When the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction also causing the sensory hairs to bend. Within the utricle is a small 2 by 3 mm patch of hair cells called the macula utricle. The macula utricle, which lies horizontally on the floor of the utricle, contains the hair cells. These hair cells are mechanoreceptors which consist of 40 to 70 steriocilia and only one true cilium called a kinocilium. The kinocilium is the only sensory aspect of the hair cell and is what causes hair cell polarization. The tips of these steriocilia and kinocilium are embedded in a gelatinous otolithic membrane. This membrane is weighted with calcium carbonate-protein granules called otoliths. The otolithic membrane adds weight to the tops of the hair cells and increases their inertia. The addition in weight and inertia is vital to the utricle's ability to detect linear acceleration, as described below, and to determine the orientation of the head. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Utricle (ear)」の詳細全文を読む スポンサード リンク
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