The inner ear ( inner ear , internal auris ) is the innermost part of the vertebrate ears. In vertebrates, the inner ear is primarily responsible for detection and sound balance. In mammals, it consists of a labyrinth of bones, a hollow cavity in the skull's temporal bone with a channel system consisting of two main functional parts:
- Cochlear, dedicated to hearing; changing the sound pressure pattern from the outer ear into an electrochemical impulse that is passed on to the brain through the auditory nerve.
- The vestibular system, dedicated to balancing
The inner ear is found in all vertebrates, with large variations in form and function. The inner ear is innervated by the eighth cranial nerves in all vertebrates.
Video Inner ear
Structure
The maze can be divided by layer or by region.
Bony vs. membranous
The labyrinth of bones, or osseous labyrinth, is a network of channels with bony walls coated with periosteum. The membranous labyrinth walks inside the labyrinth of bones. There is a layer of perilymph fluid between them. The three parts of the labyrinth of bones are the ears of the ear, the semicircular canal, and the cochlea.
Vestibular vs. cochlear
In the middle ear, the energy of the pressure wave translates into mechanical vibration by three auditory ossicles. The pressure waves move the tympanic membrane which in turn removes the malleus, the first bone of the middle ear. Malleus articulates with incus connected to stapes. The footrest of the stapes is connected to the oval window, the beginning of the inner ear. When the stapes hit the oval window, it causes perilymph, the inner ear fluid to move. The middle ear serves to convert the energy from sound pressure waves to strengths in the inner ear perilymph. The oval window has only about 1/18 of the tympanic membrane area and thus produces a higher pressure. The cochlea propagates these mechanical signals as waves in liquids and membranes, and then converts them into nerve impulses transmitted to the brain.
The vestibular system is the area of ​​the inner ear where the semicircular canal meets, close to the cochlea. The vestibular system works with visual systems 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 information from all these systems to create a sense of balance.
The inner ear vestibular system is responsible for the sensation of balance and movement. It uses the same type of fluid and cell detector (hair cell) as the cochlea uses, and sends information to the brain about the head's rotational, rotational, and movement. The type of movement or attitude detected by the hair cell depends on the corresponding mechanical structure, such as a curved tube of a semicircular canal or a calcium carbonate (otolith) crystal of saccule and utricle.
Development
The human inner ear develops during the fourth week of embryonic development of the auditory placode, the thickening of the ectoderm that causes bipolar neurons in the cochlear and vestibular ganglion. When the auditory placode invades the embryonic mesoderm, it forms the auditory vesicles or otocyst .
The hearing vesicle will give rise to the utricular and sulular components of the membranous labyrinth. They contain sensory and otolith hair cells from the utricular and saccule macules, respectively, that respond to linear acceleration and gravitational forces. The utricular division of the auditory vesicles also responds to angular acceleration, as well as endolymphatic sacs and channels connecting the saccule and utricle.
Beginning in the fifth week of development, the auditory vesicles also give rise to the cochlear ducts, which contain the Corti and endolymph spiral organs accumulated in the membranous labyrinth. The vestibular wall will separate the cochlear duct from the perilymphatic vestibular scala, a cavity inside the cochlea. The basilar membrane separates the cochlear duct from the tympani scala, a cavity in the cochlear labyrinth. The lateral wall of the cochlear ducts is formed by the spiral ligaments and stria vasculature, which produce endolymph. The hair cells develop from the lateral and medial backs of the cochlear ducts, which together with the tectorial membrane form the organ of Corti.
Histology
The Rosenthal canal or the cochlear spiral duct is part of a labyrinth of inner ear bones that is approximately 30 mm long and makes 2¾ turns about modiolus.
There are several types of special cells in the inner ear. Among these are hair cells, pillar cells, Boettcher cells, Claudius cells and Deiters cells (phalangeal cells).
Hair cells are the primary auditory receptor cells and they are also known as auditory sensor cells, acoustic hair cells, auditory cells or Corti cells. Corti organs are coated with one row of deep hair cells and three rows of hair cells outside. Hair cells have hair bundles on the apical surface of the cell. The hair bundle consists of actin-based stereocilia composition. Each stereocilium inserts as a root into a solid filament mesh actin known as a polar plate. This bundle interference causes hearing loss and balance defects.
Pill cells are found in Corti organs and serve as supporting cells for hair cells. They are divided into two types: inside and outside. The outer pillar cells are unique because the free cells stand without contact with adjacent cells except on the base and apex. Both types of pillar cells are characterized by the presence of thousands of microtubules and crosslinked actin filaments with parallel orientation. They provide a mechanical coupling between the basement membrane and the mechanoreceptors in the hair cells.
Boettcher cells are found in Corti organs where they are only present at the bottom turns of the cochlea. They lie on the basilar membrane under the Claudius cells and are organized in rows by the number of rows whose numbers vary between species. The cells interdigitate with each other, and microvilli projects into the intercellular space. They support cells for hearing hair cells in Corti organs. They were named after the German pathologist Arthur BÃÆ'¶ttcher (1831-1889).
Claudius cells are found in Corti's organ located above the line of Boettcher cells. Like Boettcher cells, they are thought to favor cells for hearing hair cells in Corti organs. They contain a variety of aquaporin waterways and appear to be involved in ion transport. They also play a role in sealing the endolymphatic space. They were named after the German anatomist Friedrich Matthias Claudius (1822-1869).
Cell deiters (phalangeal cells) are a type of neuroglial cell found in a Corti organ and organized in a single line of deep phalangeal cells and three phalangeal outer cell lines. They are the supporting cells of the hair cell area inside the cochlea. They were named after the German pathologist Otto Deiters (1834-1863) who described them.
Hensen cells are high columnar cells directly adjacent to the third row of Deiters cells.
The Hensen line is part of the tectorial membrane above the inner hair cell.
Nuel space refers to a fluid filled space between the outer pillar cells and adjacent hair cells as well as the space between the outer hair cells.
Hardesty membrane is the closest tectoral layer to the reticular lamina and above it the outer hair cell area.
The Reissner membrane consists of two layers of cells and separates the scala media from scala vestibuli.
Huschke's teeth are a tooth-shaped protrusion on the spiral limbus in contact with tectoria and separated by interdental cells.
Maps Inner ear
Physiology
The neurons in the ear respond to a simple tone, and the brain acts to process an increasingly complex sound. The average adult can usually detect sounds ranging between 20 and 20,000 Hz. The ability to detect high pitch sounds decreases in older humans.
The human ear has evolved with two basic tools for encoding sound waves; each apart in detecting high and low frequency sounds. Georg von BÃÆ'Ã… © kÃÆ' Â © sy (1899-1972) used a microscope to examine the basilar membrane that lies within the ear-in carcass. He found that the basilar membrane movement resembles the traveling waves; the shape varies by pitch frequency. At low frequency sound, the tip (peak) of the membrane moves at most, while at high frequency, the base of the membrane moves at most.
Clinical interests
Interference with or labyrinth infection can cause a disease syndrome called labyrinthitis. Symptoms of labyrinthitis include temporary nausea, disorientation, vertigo, and dizziness. Labyrinthitis can be caused by viral infections, bacterial infections, or physical blockage of the inner ear.
Another condition has been known as autoimmune ear disease (AIED). It is characterized by idiopathic bilateral sensorineural hearing loss, rapidly progressive. This is a fairly rare disorder while at the same time, the lack of a proper diagnostic test means the exact incident can not be determined.
Comparative anatomy
Birds have a hearing system similar to mammals, including cochlea. Reptiles, amphibians, and fish do not have cochleas but hear with a simpler hearing organ or vestibular organ, which generally detects lower frequency sounds than cochlear.
Cochlear system
In reptiles, the sound is transmitted to the inner ear by the stapes (stirrup) of the middle ear bone. It is pressed into an oval window, a closed membrane opening on the surface of the front room. From here, sound waves are made through a short perilymphatic duct to the second opening, a round window, equalizing the pressure, allowing noncompressible fluid to move freely. Walking parallel to the perilymphatic tract is a separate blind end channel, lagena , filled with endolymph. Lagena is separated from the perilymphatic tract by a basilar membrane, and contains sensory hair cells that eventually translate the vibrations in the fluid into a neural signal. It is attached to one end to the saccule.
In most reptiles, the perilymphatic tract and lagena are relatively short, and the sensory cells are confined to the small basilar papillae that lie between them. However, in birds, mammals, and crocodiles, this structure becomes much larger and somewhat more complicated. In birds, crocodiles, and monotremata, channels are only extended, together forming long tubes, more or less straight. Endolymphatic ducts are wrapped in a simple circle around the lagoon, with the basilar membrane lying on one side. The first half of the channel is now referred to as scala vestibuli, while the second half, which includes the basilar membrane, is called scala tympani. As a result of this increase in length, the basilar and papillary membranes are expanded, with the latter developing into a Corti organ, while lagena is now called the cochlear ducts. All these structures together form a cochlea.
In mammals (other than monotremes), the cochlea is extended further, into a circular structure to accommodate its length inside the head. Corti organs also have more complex structures in mammals than in other amniotes.
The setting of the inner ear of a living amphibian, in many ways, is similar to a reptile. However, they often lack basilar papillae, have separate sensory cell clusters at the upper edge of the saccule, referred to as papilla amphibiorum , which seems to have the same function.
Although many fish are capable of hearing, lagena is, at best, a short diverticulum of saccule, and seems to have no role in sound sensation. Different groups of hair cells inside the inner ear can even be responsible; for example, bony fish contains a sensory cluster called macula neglecta in utriculus that may have this function. Although the fish has no outer or middle ear, the sound may still be transmitted to the inner ear through the skull bone, or by the swim bladder, the part that often lies close inside the body. Vestibular System
Compared to the cochlear system, the vestibular system varies relatively little between different groups of jawed vertebrates. The central part of the system consists of two chambers, saccule and utricle, each of which includes one or two small groups of sensory hair cells. All jawed vertebrates also have three semicircular canals arising from utriculus, each with an ampule containing sensory cells at one end.
Endolymphatic channels flow from the saccule up through the head, and end close to the brain. In cartilaginous fish, this channel actually opens onto the top of the head, and in some teleost, it is just the blind end. However, in all other species, it ends up in the endolymphatic sac. In many reptiles, fish, and amphibians, these pouches can reach considerable size. In amphibians the sacs of both sides can converge into a single structure, which often extends to the length of the body, parallel to the spinal canal.
Lamprey primitives and hagfish, however, have a simpler system. The inner ear of this species consists of a single vestibular space, although in lampreys, it is associated with a series of sacs covered with cilia. Lamprey only has two semicircular canals, with no horizontal canals, while the hagfish has only a single, vertical channel.
Equilibrium
The inner ear is primarily responsible for balance, equilibrium and orientation in three-dimensional space. The inner ear can detect static and dynamic equilibrium. Three semicircular ducts and two chambers, which contain saccule and utricle, allow the body to detect deviations from equilibrium. Makula sacculi detects vertical acceleration while the utriculi macule is responsible for horizontal acceleration. This microscopic structure has stereocilia and one kinocilium located within the gelatin otolytic membrane. The subsequent membrane is weighed with otolite. Stereocilia and kinocilium movements allow the saccula and utricle hair cells to detect motion. The semicircular duct is responsible for detecting rotational motion.
Additional images
See also
- The ears
- Hear
- Outer ear
- Middle ear
References
- Ruckenstein, M. J. (2004). "Ear Disease In Autoimmune". Current Opinion at Otolaryngology & amp; Head and Neck Surgery, 12 (5), pp.Ã, 426-430.
Saladin, "Anatomy and Physiology" 6e, printed American Speech-Language-Hearing Association, The Middle Ear, http://www.asha.org/public/hearing/Middle-Ear/
External links
Photo anatomy: 30: 05-0101 at SUNY Downstate Medical Center
Source of the article : Wikipedia
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