London – The auditory system is the first of the five senses that develop in the foetus.

It has several functions, the most important is the encoding of external signals can undertake the meaning. Sound perception is probably the most important function because it enables all the anatomical features that allow alert humans to survive.

To encode signals is necessary a transformation of the sound energy into electrical energy and that they are recoded in digital form, the only recognizable from the Central auditory system.

This complex apparatus consists of: the outer ear, middle ear, basilar membrane of the inner ear, inner ear.

The first three constitute the Transmission apparatus, whose function is to transfer energy so that there is adequate stimulation of energy transducers. This is done mainly in the inner ear where happens the analogic analysis of the message, the transformation of energy and the message recoding in digital language.

At this point the stimulus is transferred to the auditory nerve, which in turn sends it to the central nerve structures. As we mentioned at the beginning, the auditory system is formed from the outer ear, composed by: auricle, external auditory canal and tympanic membrane.

More internally than the outer ear is the middle ear, that is formed by a tympanic cavity in which there is the ossicular chain that send the tympanic vibrations to a second membrane.

Membrane vibrations to ossicular chain will cause similar movements on the oval window, behind which there are inner ear fluids.
The movement of liquids form a wave that propagates to the Basilar membrane, on which there are the hair cells that convert mechanical energy into electrical energy.
The inner ear has two types of cells that are divided into external and internal. The external cells are active when receive sounds from 0-60 dB and are able to maximize sounds at low and high intensity inside cells. The hair cells are connected to the auditory nerve fibers which are triggered whenever they are stimulated. Activated nerve, transfer the stimulus to the central nervous system, that makes man conscious of the received message. Pathogen damage can affect all parts of the apparatus, causing various types of deafness of varying complexity. According to the radius of action of pathogenic damage there are difficulties in listening, more or less acute.
Hence derive the hearing loss, distinguishable in communicable and perceptual.