How does hearing work?
The ear includes receptors for hearing and balance. The physiological function of the ear in terms of hearing is described very briefly below and of balance in the corresponding section.
Overall the ear is illustrated below.
The ear consists
Outer ear
Sound is transmitted as sound waves from the environment. Sound waves are collected from the outer ear and more specifically from the auricle (or pinna) and sent through a tube called the external auditory canal to the eardrum. The pinna and the external auditory canal form the outer ear or outer ear which is separated by the tympanic membrane or eardrum from the middle ear.
Inner ear
The footplate of the stapes is attached to the oval window (part of the inner ear). The movement of the stapes transmits the sound wave to the inner ear. The inner ear includes the snail-like organ called cochlea, which is the main organ of hearing, and the vestibule (containing utricle and saccule) and the semicircular canals, which are the main organs of balance.
The cochlea includes a system of special cell types: the inner and outer hair cells which are arranged on a membrane (basilar membrane) and supporting cells. Many of the functions of these cells and some parts of the auditory system in general are not well known and are the subject of research. The inner ear naturally contains fluid, unlike the middle and outer ear.
The movement of the fluid in the inner ear (inner ear) causes the hair cells in the cochlea to bend. The hair cells convert the movement into electrical signals (conversion of mechanical energy into electrical energy).
This electrical activity is transmitted to the auditory nerve and to the brain, where it is interpreted as sound.
The brain compares the information it receives from both ears and it identifies the direction of the source of the sound whether it is coming from the left or the right.
How is hearing measured?
Hearing is measured in dBHL (decibel hearing level) and not as a percentage (%).
The measurement is done with special machines called audiographs.
It is a painless procedure which is ideally carried out in a soundproof room or in a quiet room where the ENT doctor or audiologist delivers, through special earphones placed in the ears of the person who is tested, sine waves (simple sounds) of a specific intensity per frequency (250-8000Hz - classical audiometry).
Pure tone / classical audiometry can measure hearing up to 8000 Hz but more specialized tests called extended audiometry is a test that can measure hearing up to 16000Hz (high-frequency audiometry).
The specialist turns the volume up and down until the sound is barely audible. This point is called the hearing threshold and is marked on a diagram called the audiogram.
You can see an audiogram on the picture.
For toddlers the same procedure is called play audiometry and the toddler is asked to do something with a toy every time the sound is heard. Child’s cooperation is important for the test.
