Saccule
Encyclopedia
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 (for example, 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 saccule is located within the loose areolar tissue of the pre-epiglottic space. This is filled with an abundance of mucous glands, up to sixty to seventy in numbers.
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.
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 cell
s, 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.
s.
The saccule is located within the loose areolar tissue of the pre-epiglottic space. This is filled with an abundance of mucous glands, up to sixty to seventy in numbers.
The vestibular system is important in maintaining balance
Balance (ability)
In biomechanics, balance is an ability to maintain the center of gravity of a body within the base of support with minimal postural sway. When exercising the ability to balance, one is said to be balancing....
, or equilibrium
Equilibrioception
Equilibrioception or sense of balance is one of the physiological senses. It helps prevent humans and animals from falling over when walking or standing still. Balance is the result of a number of body systems working together: the eyes , ears and the body's sense of where it is in space ideally...
. The vestibular system includes the saccule, utricle, and the three semicircular canals. The vestibule
Vestibule of the ear
-Definition:The vestibule is the central part of the osseous labyrinth, and is situated medial to the tympanic cavity, behind the cochlea, and in front of the semicircular canals.The etymology comes from the Latin vestibulum, literally an entrance hall....
is the name of the fluid-filled, membranous duct than contains these organs of balance. The vestibule is encased in the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...
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 vestibuliScala vestibuli
Scala vestibuli is a perilymph-filled cavity inside the cochlea of the inner ear that conducts sound vibrations to the scala media.It is separated from the scala media by Reissner's membrane and extends from the vestibule of the ear to the helicotrema where it joins scala tympani.-External links:* ...
of the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
. 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
Vestibulocochlear nerve
The vestibulocochlear nerve is the eighth of twelve cranial nerves, and is responsible for transmitting sound and equilibrium information from the inner ear to the brain...
, also known as the acoustic nerve or cranial nerve VIII.
Within the macula are hair cell
Hair cell
Hair cells are the sensory receptors of both the auditory system and the vestibular system in all vertebrates. In mammals, the auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear...
s, each having a hair bundle on the apical aspect. The hair bundle is composed of a single kinocilium
Kinocilium
A kinocilium is a special type of cilium on the apex of hair cells located in the sensory epithelium of the vertebrate inner ear.-Anatomy in humans:...
and many (at least 70) stereocilia
Stereocilia
In the inner ear, stereocilia are the mechanosensing organelles of hair cells, which respond to fluid motion in numerous types of animals for various functions, including hearing and balance. They are about 10–50 micrometers in length and share some similar features of microvilli...
. 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
Otolithic membrane
The otolithic membrane is a gelatinous membrane located in the vestibular apparatus of the inner ear, and plays an essential role in the brain's interpretation of equilibrium....
, 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
Petrous portion
Petrous portion can refer to:* Petrous portion of the temporal bone* Petrous portion of the internal carotid artery...
of the temporal bone
Temporal bone
The temporal bones are situated at the sides and base of the skull, and lateral to the temporal lobes of the cerebrum.The temporal bone supports that part of the face known as the temple.-Parts:The temporal bone consists of four parts:* Squama temporalis...
, where it is in contact with the dura mater
Dura mater
The dura mater , or dura, is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for...
.
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 orientate 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 cellHair cell
Hair cells are the sensory receptors of both the auditory system and the vestibular system in all vertebrates. In mammals, the auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear...
s.