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The utricle is a small membranous sac (part of the membranous labyrinth) and paired with the saccule lies within the vestibule of the inner ear. It has an important role in orientation and static balance, particularly in horizontal tilt.
The vestibule is located within the bony labyrinth (temporal bone) of the inner ear 2 (inferior to the semicircular canals 1). The utricle and the saccule are co-located within the vestibule 3. The utricle lies on the medial wall of the vestibule and is in contact with the recessus ellipticus 2. It is larger in size compared to the saccule. The utricle communicates with the saccule via the utriculosaccular duct 1.
Lying horizontally on the floor of the utricle lies a projection known as the macula, the sensory organ of the utricle 4. This sensory epithelium is lined by vestibular cells which are mechanoreceptors, containing stereocilia and kinocilia (hair cells and supporting cells respectively) 2. These cells project into the membranous labyrinth called the statoconial membrane, a gelatinous layer beyond containing otoliths (calcium carbonate particles) 2,4. Cilia from the hair cells are attached to these otoliths 2.
Any change in the orientation of the head results in stimulation of the utricle, via movement in the otolith-cilia-macula complex, releasing signals that the brain interprets 2,4. The utricle is more sensitive to horizontal acceleration in comparison to the saccule, which is more sensitive to vertical acceleration 1,4.
The anterior vestibular artery is the second branch of the labyrinthine artery. This artery supplies the utricle 1.
The mechanoreceptors of the utricle are connected to the nervous system by fibers of the vestibular division of the vestibulocochlear nerve (VIII) 1.
The utricle itself is too small to be distinguished on high-resolution CT or MRI 6, but sits in the medial portion of the vestibule.
Damage to the otolith-containing organs, such as the utricle, can result in a reduced ability to sense motion and orientation, leading to vestibular symptoms e.g. imbalance 5.
- 1. Shields G. Vestibular Function and Anatomy. 2004. Grand Rounds Presentation, Department of Otolaryngology at University of Texas Medical Branch. https://www.utmb.edu/otoref/grnds/Vestibular-2004-0414/Vestibular-2004-0414.pdf
- 2. Stephen M. Highstein, Gay R. Holstein. The Anatomical and Physiological Framework for Vestibular Prostheses. (2012) The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology. 295 (11): 2000. doi:10.1002/ar.22582 - Pubmed
- 3. Institute for Quality and Efficiency in Health Care. How does our sense of balance work?. (2017). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4039022/
- 4. Dale Purves, George J Augustine, David Fitzpatrick, Lawrence C Katz, Anthony-Samuel LaMantia, James O McNamara, S Mark Williams. The Otolith Organs: The Utricle and Sacculus. (2018). https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072578/
- 5. Pelosi S, Schuster D, Jacobson GP, Carlson ML, Haynes DS, Bennett ML, Rivas A, Wanna GB. Clinical characteristics associated with isolated unilateral utricular dysfunction. (2013) American journal of otolaryngology. 34 (5): 490-5. doi:10.1016/j.amjoto.2013.04.008 - Pubmed
- 6. Juliano AF, Ginat DT. Imaging Review of the Temporal Bone: Part I. Anatomy and Inflammatory and Neoplastic Processes. Radiology. 2013:269(1);17-33 Online article (free access) - PDF