page_title: Utricle (ear)
section_title: Structure
hierarchical_section_title: Utricle (ear) / Structure
caption_attribution_description: English: Internal Ear Anatomy. See a related animation of this medical topic.
context_page_description: The utricle and saccule are the two otolith organs in the vertebrate inner ear. They are part of the balancing system in the vestibule of the bony labyrinth. They 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. The word utricle comes from Latin uter, meaning 'leather bag'.
context_section_description: 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 of 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 latitudinal 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 of utricle. The macula of 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 stereocilia 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 stereocilia 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.
caption: Inner ear, showing utricle near centre
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