Name = Saccule
Latin = sacculus
GraySubject = 232
GrayPage = 1052
Caption = illustration of otolith organs showing detail of
utricle, ococonia, endolymph, cupula, macula, hair cellfilaments, and saccular nerve
MapPos = Saccule
MeshName = Saccule+and+Utricle
MeshNumber = A09.246.631.909.625 |
The saccule is a bed of sensory cells situated in the inner ear. The saccule translates head movements into neural impulses which the brain can interpret. The saccule is sensitive to linear translations of the head, specifically movements up and down (think about moving on an elevator). When the head moves vertically, the sensory cells of the saccule are disturbed and the neurons connected to them begin transmitting impulses to the brain. These impulses travel along the vestibular portion of the eighth cranial nerve to the vestibular nuclei in the brainstem.
The vestibular system is important in maintaining
balance, or equilibrium. The vestibular system includes the saccule, utricle, and the three semicircular canals. The vestibuleis the name of the fluid-filled, membranous duct than contains these organs of balance. The vestibule is encased in the temporal boneof the skull.
The saccule, or sacculus, is the smaller of the two vestibular sacs. It is globular in form and lies in the
recessus sphæricusnear the opening of the scala vestibuliof the cochlea. Its cavity does not directly communicate with that of the utricle. The anterior part of the saccule exhibits an oval thickening, the macula acustica sacculi, or macula, to which are distributed the saccular filaments of the vestibular branch of the vestibulocochlear nerve, also known as the acoustic nerveor cranial nerve VIII.
Within the macula are
hair cells, each having a hair bundleon the apical aspect. The hair bundle is composed of a single kinociliumand many (at least 70) stereocilia. Stereocilia are connected to mechanically-gated ion channels in the hair cell plasma membrane via tip links. Supporting cells are interdigitate between hair cells and secrete the otolithic membrane, a thick, gelatinous layer of glycoprotein. Covering the surface of the otolithic membrane are otoliths, which are crystals of calcium carbonate. For this reason, the saccule is sometimes called an "otolithic organ."
From the posterior wall of the saccule is given off a canal, the ductus endolymphaticus. This duct is joined by the ductus utriculosaccularis, and then passes along the aquæductus vestibuli and ends in a blind pouch (saccus endolymphaticus) on the posterior surface of the
petrous portionof the temporal bone, where it is in contact with the dura mater.
From the lower part of the saccule a short tube, the canalis reuniens of Hensen, passes downward and opens into the
ductus cochlearisnear its vestibular extremity.
The saccule gathers sensory information to orient the body in space. It primarily gathers information about linear movement in the vertical plane. The structures that enable to saccule to gather this vestibular information are the
hair cells. When the head tilts, the otolithic membrane slides over the hair cells in the direction of the tilt. This sliding bends the hair bundles of the hair cells, which causes stretching of the tip links and opening of the mechanically gated ion channels. Cations such as K+ rush into the hair cell cytosol, depolarizing it. Depolarization induces opening of voltage-gated Ca2+ channels at the basal aspect of the hair cell, which triggers exocytosisof neurotransmitterto the vestibular neurons. These impulses are communicated via the vestibular nerve to vestibular nuclei in the brainstemand medulla. Impulses are also carried to the cerebellumvia the inferior cerebral peduncles.
* Tortora, G. J. & Derrickson, B. (2006). "Principles of Anatomy and Physiology," 11th Edition. John Wiley and Sons, Inc.
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Look at other dictionaries:
saccule — [ sakyl ] n. m. • 1847; lat. sacculus « petit sac » ♦ Anat. Vésicule placée à la partie inférieure du vestibule de l oreille interne. ● saccule nom masculin (latin sacculus, petit sac) Organe membraneux situé dans le vestibule de l oreille… … Encyclopédie Universelle
Saccule — Sac cule, n. [L. sacculus, dim. of saccus sack.] A little sac; specifically, the sacculus of the ear. [1913 Webster] … The Collaborative International Dictionary of English
saccule — [sak′yo͞ol] n. [L sacculus, dim. of saccus, SACK1] a small sac; esp., the smaller of the two divisions of the membranous labyrinth of the inner ear … English World dictionary
saccule — (Order Decapoda): In antennal gland, proximalmost of two divisions (saccule, labyrinth) of end sac. Consists of simple vesicle or is partitioned internally [Stachowitsch, 1992] … Crustacea glossary
saccule — (sa ku l ) s. m. Terme d anatomie. Une des deux vésicules du vestibule membraneux de l oreille moyenne, logée dans la fossette ronde vestibulaire. Le saccule communique avec l autre vésicule et est tapissé d otoconie. ÉTYMOLOGIE Lat. sacculus … Dictionnaire de la Langue Française d'Émile Littré
saccule — noun Etymology: New Latin sacculus, from Latin, diminutive of saccus bag more at sack Date: circa 1839 a little sac; specifically the smaller chamber of the membranous labyrinth of the ear … New Collegiate Dictionary
saccule — sacculus … Dictionary of ichthyology
saccule — n. [L. dim. saccus, bag] 1. A small sac or pouch. 2. Sometimes applied to a small invagination of the cuticle … Dictionary of invertebrate zoology
saccule — /sak yoohl/, n. 1. Anat. the smaller of two sacs in the membranous labyrinth of the internal ear. Cf. utricle (def. 3). 2. a little sac. [1830 40; < L sacculus SACCULUS] * * * … Universalium
saccule — noun The smallest chamber of the membranous labyrinth of the ear … Wiktionary