Utricle (ear)
| Utricle (ear) | |
|---|---|
 |
|
| illustration of otolith organs showing detail of utricle, otoconia, endolymph, cupula, macula, hair cell filaments, and saccular nerve | |
| Components of the inner ear including the utricle | |
| Latin | utriculus |
| Gray's | subject #232 1051 |
| MeSH | Saccule+and+Utricle |
The utricle, or utriculus, 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 (membraneous labyrinth) located within the vestibule of the bony labyrinth (small oval chamber).[1] These use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation.
[edit] Anatomy
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 utricle contains mechanoreceptors called hair cells that distinguish between degrees of tilting of the head, thanks to their apical stereocilia set-up. These are covered by otolith which, due to gravity, pull on the stereocilia and tilt them. Depending on whether the tilt is in the direction of the kinocilium or not, the resulting hair cell polarisation is excitatory (depolarising) or inhibitory (hyperpolarisation), respectively. Any orientation of the head causes a combination of stimulation to the utricles and saccules of the two ears. The brain interprets head orientation by comparing these inputs to each other and to other input from the eyes and stretch receptors in the neck, thereby detecting whether only the head is tilted or the entire body is tipping. The inertia of the otolithic membranes is especially important in detecting linear acceleration. Suppose you are sitting in a car at a stoplight and then begin to move. The otolithic membrane of the macula utriculi briefly lags behind the rest of the tissues, bends the stereocilia backwards, and stimulates the cells. [2]This signal to the vestibular nerve (which takes it to the brainstem) does not adapt with time. The effect of this is that, for example, an individual lying down to sleep will continue to detect that they are lying down hours later when they awaken.
Labyrinthine activity responsible for the nystagmus induced by off-vertical axis rotation arises in the otolith organs and couples to the oculomotor system through the velocity storage mechanism.[3]
That portion which is lodged in the recess forms a pouch or cul-de-sac, the floor and anterior wall of which are thickened and form the macula acustica utriculi, which receives the utricular filaments of the acoustic nerve.
The cavity of the utricle communicates behind with the semicircular ducts by five orifices.
The ductus utriculosaccularis comes off of the anterior wall of the utricle and opens into the ductus endolymphaticus.
[edit] References
- ^ Moores, Kieth L. "Essential Clinical Anatomy" Lippincott Williams & Wilkins; Second Edition edition (2002).
- ^ Saladin, Kenneth S. Anatomy & Physiology: the Unity of Form and Function. Dubuque: McGraw-Hill, 2010. Print.
- ^ Cohen, B., J. Suzuki, and T. Raphan. "Role of the Otolith Organs in Generation of Horizontal Nystagmus: Effects of Selective Labyrinthine Lesions." Brain Research 276.1 (1983): 159-64. Print.
[edit] External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
|
|||||||||||||||||||||||||||||||||||||||||||
