Utricle
Encyclopedia
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). These use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation.
, 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. 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.
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.
Saccule
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...
is one of the two otolith
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
organs located in the vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
. The utricle and the saccule are parts of the balancing apparatus (membraneous labyrinth) located within the vestibule of the bony labyrinth (small oval chamber). These use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation.
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 vestibuleVestibule 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....
, 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
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...
set-up. These are covered by otolith
Otolith
An otolith, , also called statoconium or otoconium is a structure in the saccule or utricle of the inner ear, specifically in the vestibular labyrinth of vertebrates. The saccule and utricle, in turn, together make the otolith organs. They are sensitive to gravity and linear acceleration...
which, due to gravity, pull on the stereocilia and tilt them. Depending on whether the tilt is in the direction of the 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:...
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. 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.
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.
