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The utricle of the membranous labyrinth (or simply utricle, Latin: utriculus) is a part of the balancing apparatus situated within the vestibule of the inner ear. The receptors within the utricle detect linear accelerations.
Structure of utricle
The utricle is an irregular, dilated sac lying in the upper and posterior part of the vestibule. It serves as the base for the three semicircular ducts. On the superior and posterior walls, the utricle has openings corresponding to the openings of the vestibule; from here, the semicircular ducts emerge.
The utricle contains a sensory epithelium - the macula, which is composed of hair cells and associated supporting cells.
The macula of the utricle is a small layer of sensory epithelium containing receptor hair cells lying horizontally on the floor of the utricle. The epithelium is rich with cilia and otholites.
The hair cells are mechanoreceptors embedded in a gelatinous otolithic membrane that adds weight to the tops of the hair cells, increasing their inertia.
The otolithic membrane is crucial for the utricle to detect linear acceleration, such as rapid lateral displacements and sideways head tilts. The nerve responsible for transmitting this information is the utricular nerve, a branch of the utriculo-ampullary nerve.