The ear is the organ that is used to capture sound and is the headquarters of the sense of hearing, but it also plays an important role in the balance. The word ear can refer to the entire system that makes the collection and understanding of sounds, or to the outside only.
The ear of mammals
Most mammals, including humans, have two ears, one on each side of the head. Their main ingredients are:
* Os lenticular
* Oval Window
* Round Window
* Eustachian tube
* Scala Tympani
* Scala vestibuli
* Nerve Fiber
* Semi-circular canals
These components are divided into three distinct anatomical regions: external ear, middle and internal.
The external ear
The outer ear consists of two segments: the flag and the ear
* The flag is a blade fold in on itself in various meanings, Oval Big top with a whole in the form of a flag of acoustic horn. The pavilion has a skeleton made of cartilage elastic allowing it to resume its normal position after a deflection. At this level there is no subcutaneous tissue. The lower the flag is represented by the ear lobe which is the central fat, low innerve and richly vascularise.
* The ear is shaped like a horn sound diminishing in diameter as it moves closer to the bottom ie the eardrum. Its two-thirds have an external cartilaginous skeleton while its internal third has a skeleton bone in the membrane temporale (bone air). The inner part is coated with a skin with many pores and sebaceous glands and apocrine sweat glands (glands cerumineuses) that produce a liquid protein and glucolipidique, pigmented and sticky, wax.
The middle ear
It includes the eardrum (tympanum) and the ossicles (the "chain ossiculaire"), three very small bones. They are called respectively the hammer (Malleus), the anvil (incus) and the stirrup (stapes, which is the smallest bones of the human body). These names come from their characteristic forms. The hammer and the anvil form a joint inflexible incudo-called block maleaire.
The sounds are the result of vibration of air in the ear that have the effect of vibrating the eardrum. These vibrations are then passed along the chain ossiculaire, then the inner ear through the oval window.
The design which currently dominates the spread of vibrations in the middle ear is that of Khana and Tonndorf developed in 1972: roughly, the lines of concentric zones of iso-amplitude of certain frequencies are parallel to the handle of the hammer, with the membrane of the eardrum, areas of vibration more for this race.
Since the middle ear is hollow, an environment of high pressure (like water) pose the risk of puncture the eardrum. Mitigate this risk is the function of the eustachian tubes. Evolutionary descendants of respiratory gills of fish, these tubes connect the middle ear to the nasal cavity to decompress the middle ear.
The inner ear
It contains not only the organ of hearing, or cochlea cochlea (cochlea), but the vestibule, body balance, responsible for the perception of the position of the head and its acceleration. The movement of the stapes is transmitted to the cochlea via the oval window and the vestibule.
The cochlea is a hollow filled with a liquid called endolymph. It is lined with hair cells - sensory cells of non-renewable capped filamentous structures, the stereocilia, grouped into a clump free to vibrate cilia. These cells are arranged along a membrane (basilar membrane) that the cochlea is partitioned into two rooms. All the hair cells and membranes that are attached is the organ of Corti.
The basilar membrane and hair cells that it is set in motion by vibrations transmitted through the middle ear. Along the cochlea, each cell responds preferentially to a certain frequency, allowing the brain to differentiate the pitch of notes. Thus, the hair cells near the base of the cochlea (oval window, close to the middle ear) preferentially respond to acute. Those in its apex (last round of the cochlea) contrary to respond to low frequencies.
These are the hair cells that are transduction mecanoelectrique: they transform their movement tuft ciliary nerve signal by the auditory nerve, which will be interpreted by the brain as sound pitch corresponding to the cell excited.
The vestibular apparatus consists of three semicircular canals, orthogonally arranged within three shots. They are filled with the same endolymph that the cochlea. When the ear is subject to a movement, the inertia of the liquid makes this movement detected by hair cells, very similar to the cochlea. The arrangement of three channels in three orthogonal planes can detect the position of the head in all directions.
Diseases of the ear and hearing
The medical-surgical specialty concerned with the pathology of the ear is ear-Rhyno laryngology (ENT)
* Tinnitus (tinnitus)
* Antrite or more precisely otitis media (otitis media)
* Ear infections
* Labyrinthitis (otitis interna)
* Disease Menière
* The acoustic neuroma
* Neurofibromatosis Type II
* Idiopathic sudden hearing loss
* Loss of hearing due to noise
* Polychondrite chronic Atrophicans
* Deafness perception
* Disturbing the balance
* Dizziness otolithic