Product Code Database
The inner ear ( internal ear, auris interna) is the innermost part of the vertebrate ear. In , the inner ear is mainly responsible for sound detection and balance.Torres, M., Giráldez, F. (1998) The development of the vertebrate inner ear. Mechanisms of Development 71 (1–2) pp. 5–21 In , 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:J.M. Wolfe et al. (2009). Sensation & Perception. 2nd ed. Sunderland: Sinauer Associated Inc
The inner ear is found in all vertebrates, with substantial variations in form and function. The inner ear is innervated by the eighth cranial nerve in all vertebrates.
The vestibular system is the region of the inner ear where the semicircular canals converge, close to the cochlea. The vestibular system works with the visual system to keep objects in view when the head is moved. Joint and muscle receptors are also important in maintaining balance. The brain receives, interprets, and processes the information from all these systems to create the sensation of balance.
The vestibular system of the inner ear is responsible for the sensations of balance and motion. It uses the same kinds of fluids and detection cells (hair cells) as the cochlea uses, and sends information to the brain about the attitude, rotation, and linear motion of the head. The type of motion or attitude detected by a hair cell depends on its associated mechanical structures, such as the curved tube of a semicircular canal or the calcium carbonate crystals (otolith) of the saccule and utricle.
The auditory vesicle will give rise to the utricular and saccular components of the membranous labyrinth. They contain the sensory hair cells and of the macula of utricle and of the saccule, respectively, which respond to linear acceleration and the force of gravity. The utricular division of the auditory vesicle also responds to angular acceleration, as well as the endolymphatic sac and duct that connect the saccule and utricle.
Beginning in the fifth week of development, the auditory vesicle also gives rise to the cochlear duct, which contains the spiral organ of Corti and the endolymph that accumulates in the membranous labyrinth. The vestibular wall will separate the cochlear duct from the perilymphatic scala vestibuli, a cavity inside the cochlea. The basilar membrane separates the cochlear duct from the scala tympani, a cavity within the cochlear labyrinth. The lateral wall of the cochlear duct is formed by the spiral ligament and the stria vascularis, which produces the endolymph. The hair cells develop from the lateral and medial ridges of the cochlear duct, which together with the tectorial membrane make up the organ of Corti.
Specialized inner ear cell include: hair cells, pillar cells, Boettcher's cells, Claudius' cells, spiral ganglion neurons, and Deiters' cells (phalangeal cells).
The hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti. The organ of Corti is lined with a single row of inner hair cells and three rows of outer hair cells. The hair cells have a hair bundle at the apical surface of the cell. The hair bundle consists of an array of actin-based stereocilia. Each stereocilium inserts as a rootlet into a dense filamentous actin mesh known as the cuticular plate. Disruption of these bundles results in hearing impairments and balance defects.
Inner and outer pillar cells in the organ of Corti support hair cells. Outer pillar cells are unique because they are free standing cells which only contact adjacent cells at the bases and apices. Both types of pillar cell have thousands of cross linked and actin filaments in parallel orientation. They provide mechanical coupling between the basement membrane and the on the hair cells.
Boettcher cell are found in the organ of Corti where they are present only in the lower turn of the cochlea. They lie on the basilar membrane beneath Claudius' cells and are organized in rows, the number of which varies between species. The cells interdigitate with each other, and project microvillus into the intercellular space. They are supporting cells for the auditory hair cells in the organ of Corti. They are named after German pathologist Arthur Böttcher (1831–1889).
Claudius cell are found in the organ of Corti located above rows of Boettcher's cells. Like Boettcher's cells, they are considered supporting cells for the auditory hair cells in the organ of Corti. They contain a variety of aquaporin water channels and appear to be involved in ion transport. They also play a role in sealing off endolymphatic spaces. They are named after the German anatomist Friedrich Matthias Claudius (1822–1869).
Deiters cell (phalangeal cells) are a type of cell found in the organ of Corti and organised in one row of inner phalangeal cells and three rows of outer phalangeal cells. They are the supporting cells of the hair cell area within the cochlea. They are named after the German pathologist Otto Deiters (1834–1863) who described them.
Hensen cell are high columnar cells that are directly adjacent to the third row of Deiters' cells.
Hensen's stripe is the section of the tectorial membrane above the inner hair cell.
Nuel's spaces refer to the fluid-filled spaces between the outer pillar cells and adjacent hair cells and also the spaces between the outer hair cells.
Hardesty's membrane is the layer of the tectoria closest to the reticular lamina and overlying the outer hair cell region.
Reissner's membrane is composed of two cell layers and separates the scala media from the scala vestibuli.
Huschke's teeth are the tooth-shaped ridges on the spiral limbus that are in contact with the tectoria and separated by interdental cells.
The human ear has evolved with two basic tools to encode sound waves; each is separate in detecting high and low-frequency sounds. Georg von Békésy (1899–1972) employed the use of a microscope in order to examine the basilar membrane located within the inner-ear of cadavers. He found that movement of the basilar membrane resembles that of a traveling wave; the shape of which varies based on the frequency of the pitch. In low-frequency sounds, the tip (apex) of the membrane moves the most, while in high-frequency sounds, the base of the membrane moves most.
Another condition has come to be known as autoimmune inner ear disease (AIED). It is characterized by idiopathic, rapidly progressive, bilateral sensorineural hearing loss. It is a fairly rare disorder while at the same time, a lack of proper diagnostic testing has meant that its precise incidence cannot be determined.Ruckenstein, M. J. (2004). "Autoimmune Inner Ear Disease". Current Opinion in Otolaryngology & Head and Neck Surgery, 12(5), pp. 426-430.
In most reptiles the perilymphatic duct and lagena are relatively short, and the sensory cells are confined to a small basilar papilla lying between them. However, in , , and , these structures become much larger and somewhat more complicated. In birds, crocodilians, and , the ducts are simply extended, together forming an elongated, more or less straight, tube. The endolymphatic duct is wrapped in a simple loop around the lagena, with the basilar membrane lying along one side. The first half of the duct is now referred to as the scala vestibuli, while the second half, which includes the basilar membrane, is called the scala tympani. As a result of this increase in length, the basilar membrane and papilla are both extended, with the latter developing into the organ of Corti, while the lagena is now called the cochlear duct. All of these structures together constitute the cochlea.
In mammals, the lagena is extended still further, becoming a coiled structure (cochlea) in order to accommodate its length within the head. The organ of Corti also has a more complex structure in mammals than it does in other .
The arrangement of the inner ear in living is, in most respects, similar to that of reptiles. However, they often lack a basilar papilla, having instead an entirely separate set of sensory cells at the upper edge of the saccule, referred to as the papilla amphibiorum, which appear to have the same function.
Although many fish are capable of hearing, the lagena is, at best, a short diverticulum of the saccule, and appears to have no role in sensation of sound. Various clusters of hair cells within the inner ear may instead be responsible; for example, Osteichthyes contain a sensory cluster called the macula neglecta in the utricle that may have this function. Although fish have neither an outer nor a middle ear, sound may still be transmitted to the inner ear through the bones of the skull, or by the swim bladder, parts of which often lie close by in the body.
An endolymphatic duct runs from the saccule up through the head and ending close to the brain. In cartilaginous fish, this duct actually opens onto the top of the head, and in some , it is simply blind-ending. In all other species, however, it ends in an endolymphatic sac. In many reptiles, fish, and amphibians this sac may reach considerable size. In amphibians the sacs from either side may fuse into a single structure, which often extends down the length of the body, parallel with the spinal canal.
The primitive and hagfish, however, have a simpler system. The inner ear in these species consists of a single vestibular chamber, although in lampreys, this is associated with a series of sacs lined by cilia. Lampreys have only two semicircular canals, with the horizontal canal being absent, while hagfish have only a single, vertical, canal.
==Additional images==
Vestibular system
By comparison with the system, the vestibular system varies relatively little between the various groups of gnathostome. The central part of the system consists of two chambers, the saccule and utricle, each of which includes one or two small clusters of sensory hair cells. All jawed vertebrates also possess three semicircular canals arising from the utricle, each with an osseous ampullae containing sensory cells at one end.
Equilibrium
The inner ear is primarily responsible for balance, equilibrium and orientation in three-dimensional space. The inner ear can detect both static and dynamic equilibrium. Three semicircular ducts and two chambers, which contain the saccule and utricle, enable the body to detect any deviation from equilibrium. The macula sacculi detects vertical acceleration while the macula utriculi is responsible for horizontal acceleration. These microscopic structures possess stereocilia and one kinocilium which are located within the gelatinous otolithic membrane. The membrane is further weighted with otoliths. Movement of the stereocilia and kinocilium enable the hair cells of the saccula and utricle to detect motion. The semicircular ducts are responsible for detecting rotational movement.Anatomy & Physiology The Unity of Form and Function. N.p.: McGraw-Hill College, 2011. Print.
See also
External links
|
|
