Saccule

Saccule

Infobox Anatomy
Name = Saccule
Latin = sacculus
GraySubject = 232
GrayPage = 1052


Caption = illustration of otolith organs showing detail of utricle, ococonia, endolymph, cupula, macula, hair cell filaments, and saccular nerve


Caption2 =


MapPos = Saccule
System =
MeshName = Saccule+and+Utricle
MeshNumber = A09.246.631.909.625 |

Introduction

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 vestibule is the name of the fluid-filled, membranous duct than contains these organs of balance. The vestibule is encased in the temporal bone of the skull.

Anatomy

The saccule, or sacculus, is the smaller of the two vestibular sacs. It is globular in form and lies in the recessus sphæricus near the opening of the scala vestibuli of 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 nerve or cranial nerve VIII.

Within the macula are hair cells, each having a hair bundle on the apical aspect. The hair bundle is composed of a single kinocilium and 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 portion of 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 cochlearis near its vestibular extremity.

Physiology

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 exocytosis of neurotransmitter to the vestibular neurons. These impulses are communicated via the vestibular nerve to vestibular nuclei in the brainstem and medulla. Impulses are also carried to the cerebellum via the inferior cerebral peduncles.

ee also

* Otolith


=Additional

References

* Tortora, G. J. & Derrickson, B. (2006). "Principles of Anatomy and Physiology," 11th Edition. John Wiley and Sons, Inc.

External links

* [http://alpha.ipfw.edu/histo-embryo/wwwimagefolder/utricsac.jpgDiagram]


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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

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