Ear

The ear ( auris latin AltGr οὖς, genitive ὠτός; . "Us, otos ") is a sensory organ, is taken up with the sound, so sound or noise as acoustic perception. To ear as an organ includes the organ of balance.

The term referred to the hearing organ in the human physiology all of the ears, the auditory nerves ( Nervi cochlear ) and the auditory cortex. The function of the ear leading to hearing.

Ears in general

However, nearly all the animals ears, construction and placement of the ears are different in different species.

In grasshoppers ears sit on the abdomen or legs, with cicadas on the legs and mosquitoes at the probes. Some lizard and salamander species hear with chest and lungs. Not always are external ears present when the hearing is present, for example in snakes and some seal species.

The listening area of the human ear ranges from about 16 hertz to 20,000 hertz maximum at the age of 2 to 5 years, with declines with increasing age, the ability to hear high frequencies. Among other elephants can perceive even lower frequencies, the so-called infrasound, while a number of animals such as dogs, dolphins and bats, still much higher frequencies, the ultrasonic can hear.

An object of the ears is the orientation in space, ie to localize sound sources, that is, to determine its direction and distance. Laterally incident sound reaches the ear facing more than the averted and there is loud because the averted ear is shadowed by the head. These run- time differences and level differences between the two ears are evaluated by the brain and used to determine the direction. In addition, the ear generates specific changes in the frequency response, which are also evaluated and used to determine the direction according to the direction.

Many creatures like man, though can locate existing sound sources, the orientation in space is done but especially with the help of balance and the sense of sight. Dolphins and bats have evolved, however, the sense of hearing to an upright orientation system. Both come from higher-frequency tones (up to 200 kHz) and orient yourself with the echo. This active process of orientation is called localization. When the bats hearing has virtually replaced the eyes that are in the darkness of much use.

The ear of man

Construction

In humans, the ear is divided into three areas:

  • The outer ear includes the ear cartilage, the ear, the ear lobe and the external auditory meatus or ear canal and the outer side of the eardrum. It serves not only to capture the sound, but also to encode a particular direction of incidence of the sound by spectral minima and maxima ( see localization ). The various projections and recesses of the external ear in each case form acoustic resonators can be excited with incident sound from a specific direction. This results in directional minima and maxima in the frequency spectrum of the ear signal, which are below used the front or rear of the ear for the determination of the directions up, (in the direction -determining bands).
  • For middle ear includes the eardrum and the malleus, incus and stapes. The round window connects the scala tympani of the inner ear with the middle ear. The Eustachian tube, also called the eustachian tube, connects the middle ear and nasopharynx. In the middle ear mechanical impedance conversion takes place, which allows for optimal transmission of the signal from the outer ear to the inner ear.
  • The inner ear is a small cavity system ( bony labyrinth, lat Labyrinthus osseus ) within the temporal bone, a portion of the temporal bone. In this bony labyrinth is the membranous or membranous labyrinth (Latin Labyrinthus membranaceus ), consisting of the cochlea (Latin Labyrinthus cochlear short cochlea), is converted into the sound into nerve impulses, and the organ of balance (Latin Labyrinthus vestibular ). The vestibular system consists of the semicircular canals and two vesicular fractions, the utricle and saccule. It is used to detect changes in motion and the direction of gravity. Cochlea and vestibular system are built similar: both are filled with a fluid ( endolymph ) and have hair cells. The hair cells are cylindrical and have their name from about 30 to 150 hair -like appendages at the upper end of the cell ( stereocilia ). By movements of the liquid, the hairs are bent and solve this nerve impulses. At the lower end there is a synapse with a sensory neuron. This pours out already in the idle state neurotransmitters. If now by sonic vibration or changes in motion of the head the hair extensions deflected, the amount of the neurotransmitter changes. The vestibular system, the hair extensions are covered with a jelly- type layer are deposited on the small crystals of calcium carbonate, which enhance the effect of motion. From the cochlea, the auditory nerve goes together with the nerve bundles of the vestibular organ as vestibulocochlear nerve toward the brain.

The perception of acoustic signals is materially influenced by how sound vibrations are on their way from the outer ear through the middle ear to the nerve cells of the inner ear in each case formed and processed. The human ear can perceive acoustic events only within a certain frequency and sound pressure level range. Between the hearing threshold and the pain threshold is the listening area. The sensitivity of the ear is just like its noise tolerance extraordinary.

The slightest perceptible sound pressure is about 20 micro -Pascal (20 -5 Pa uPA = 2:10 ), which corresponds to Lp = 0 dB SPL sound pressure level. These sound pressure changes Δ p are transmitted through the eardrum and converted in the ear - brain system for auditory sensation. Because the eardrum with the ear as the sensor system has the characteristics of a sound pressure receiver, describes the sound pressure level as a sound field size, the strength of the best hearing impression. The sound intensity J in W/m2 is as sound energy quantity, however, not suitable to describe the listening experience; due to the complex impedance of the outer and middle ear at the same sound pressure level. The same applies mutatis mutandis to the sound velocity.

The human ear can already take an extremely low noise performance. The slightest perceptible sound produces an output of less than 10-17 W in the inner ear. Within a tenth of a second it takes for the ear to convert this signal into nerve impulses, already a sensation is produced by an energy of about 10-18 joules. This shows how sensitive this sense organ is actually.

The threshold of pain is 130 dB SPL over, which is more than three million times the sound pressure of the smallest audible ( 63,246:0,00002 = 3.1623 million ). Nevertheless, or perhaps because the ear is very sensitive, especially the inner ear takes on a loud sound pressure damage.

When directional hearing and at the headphone Stereofonie play time differences and level differences between both ears and thus the individual ear distance a certain role, and spectral properties of the ear signals.

The techniques for testing hearing are summarized under the term audiometry. A result of a hearing test, which examines the hearing at different frequencies is called the audiogram. For this, the threshold of hearing can usually be read.

Outside of the actual ear, however, are the nerves that lead to the hearing center of the brain, as well as the auditory cortex itself are affected this, it may also be affected in a functioning ear, the sound perception.

The path of the sound: ear → ear canal → tympanic membrane → ossicles → cochlea → nerve

Diseases

The human ear can become ill on various ways that are specific to each of the affected part of the ear.

  • The outer ear is sensitive due to its relatively thin skin in the ear canal and the ear for infections with bacteria or fungi. This lead to the frequently observed ear infection (otitis externa). By weakened defense and poor treatment, the infection can on the bone surrounding the ear canal, spread and cause the suppuration.
  • There are congenital and acquired auricular deformities. The most common congenital ear malformation are the protruding ears, rare are second-or third-degree ear malformations such as microtia. Acquired auricular malformations caused by external influences, such as accidents or animal bite injuries.
  • Also, the middle ear can be affected by inflammation and suppuration. We distinguish acute otitis media from chronic otitis media. Due to the inflammation and the ossicles can be attacked and destroyed. The middle ear can still be damaged by large sound pressures as they arise in explosions. Together with the other damage caused from this one speaks of the explosion trauma.
  • Common diseases of the inner ear occur with permanent noise and blast trauma related. Here, the hair cells are damaged. The conversion of the mechanical stimuli into nerve impulses is then no longer possible, and a hearing loss is the result. In this context, often occurs tinnitus. Furthermore, the inner ear target of viral infections, such as meningitis, measles and mumps. Also, various drugs (eg, gentamicin ) can damage the inner ear. The causes of the so-called sudden hearing loss, at which a sudden hearing loss, tinnitus and vertigo may occur are unknown. Similar symptoms can also be due to a Bogengangsdehiszenz, a bone defect in the inner ear occur.

For the diagnosis of diseases of the ear in addition to the commonly used methods of medicine such as X-ray examinations, serological and visual examinations are also hearing tests available.

Ear impression

The footprint of the ears can be used to identify a person. Here, the ear mold has a similarly high probative value as a fingerprint. The criminology can based on the posthumous ear impressions, eg when listening at windows or doors, quite convict offenders. Advantage over the fingerprint is that an ear impression usually does not arise by chance. Fingerprints can usually be found by many people at the scene.

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