The ear has a double function. It allows to hear and also intervenes in an essential way in the balance. This article discusses the auditory function of the ear.
Anatomy of the ear and sound transmission
The ear is divided into three parts :
The external ear :
It is the pinna and the auditory canal. The pinna plays an essential role in the focusing of sounds (horn of Professor Sunflower). This is why an intraductal device naturally benefits from this anatomical amplifier.
The middle ear :
Includes the eardrum and the organs of transmission of the sound which are the ossicles (hammer, anvil, stirrup). Very schematically, the sound makes vibrate the eardrum which transmits these vibrations to the ossicular chain, then to the inner ear by the oval window – via the stapes.
The inner ear :
The inner ear is made up of the cochlea, or organ of hearing, which resembles the shell of a snail, and the vestibule, or organ of balance, which provides information at all times about the position of the head in relation to the body. The inner ear “decodes” the sound that reaches it and conveys it to the brain. It is the latter that will analyze and interpret it.
The different sound levels
The ear perceives sounds that can be between 20 Hz and 18000 Hz. Below these figures we speak of infrasound. Beyond that, ultrasound. Both are inaudible to the human ear.
The younger the subject is, the better he will perceive high-pitched sounds.
A few years ago, a device had appeared in France before being criticized and then abandoned. It was a high-pitched sound emitter (17000 Hz approximately) at the limit of the ultrasounds and only perceived by young ears (less than 25 years). The device was intended to prevent groups of young people from “squatting” in certain locations. Fortunately, these devices have been banned, but it is interesting to note that the aging of the ear begins very early, well before objective presbycusis for lower frequencies. The anatomical proximity of the oval window, where the stapes are inserted, to the base of the cochlea, where the cells specialized in high frequencies are located, explains this particularity.
Audiometry : a tool to test the human ear
The human ear is tested with an audiometer for frequencies between 125 Hz and 8000 Hz.
This device allows the detection of all types of deafness (conductive deafness, sensorineural deafness) and their importance. The technician or the ENT generally performs this test in a room that is as soundproof as possible and the sounds are tested one by one with the help of headphones in each ear giving rise to a characteristic curve (see our article Audiometry : measurement principle and practical applications).
We consider that an average loss of 35dB on certain frequencies is an indication of hearing aid fitting, but each individual expresses his or her own feelings, made up of denial and paradoxically, sometimes of complaints even though the damage is minimal. It is the role of the specialist to explain and advise according to these thresholds of damage.
The ear, as we have said, deteriorates very early. This degradation does not become annoying until around sixty years of age, but multiple extrinsic factors (noise, jobs, sports) or intrinsic factors (genetic, metabolic, hypertension, tobacco, osteoarthritis…) can play an amplifying role. More information on hearing prevention in our article Can we prevent hearing loss ?
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