Hearing is one of our five senses. The function of hearing is to convert sound waves to neural impulses that can be perceived by the brain as sound.
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To fully understand what a hearing loss is, it is necessary to understand how hearing and the ear function.
Sounds moving through air can be described as pressure variations or vibrations of the air molecules. These pressure variations create sound waves which can be perceived by the human ear.
The ear is responsible for hearing. It collects sound waves and convert them to neural codes which are interpreted by the brain.
The ear consists of three parts: |
 The outer ear |
| The middle ear |
| The inner ear |
The outer ear is made up of the external cartilaginous part of the ear and the ear canal.
The outer ear functions as a kind of funnel which collects sound waves and conducts them to the eardrum. The eardrum is located at the end of the ear canal and forms the boundary to the middle ear.
The middle ear is an air-filled space. The air pressure in the middle ear is regulated by the Eustachian tube, which connects the middle ear to the nose and throat. There are three small bones in the middle ear; the malleus, the incus and the stapes, commonly called the hammer, the anvil and the stirrup.
This chain of bones forms a lever mechanism, conducting the vibrations from the eardrum to the part of the inner ear that processes sound.
The inner ear is a fluid-filled bone structure shaped like a snail shell. The connection between the middle ear and the inner ear is called the oval window. The footplate of the stirrup is attached to the oval window and functions as a piston moving the fluid of the inner ear.
In the cochlea there are about 23,000 outer hair cells (sensory cells), which are activated by this movement of the fluid. When the hair cells are activated, they send impulses to the brain, which perceives these impulses as sound.
Besides the cochlea, the inner ear also houses the balance organ.
The outer ear, ear canal and middle ear collect and enhance the sound waves, which set the eardrum into motion. The mechanical vibrations of the eardrum are transmitted to the stirrup by the hammer and the anvil. The stirrup moves back and forth like a “piston” in the oval window, moving the fluid of the inner ear.
The resulting wave movements in the cochlea cause the hairs (cilia) of the hair cells in the inner ear to move. As the hair cells are stimulated, they send neural impulses via the auditory nerve to that part of the brain that is located just behind the temporal bone, commonly referred to as the hearing centre.
The frequency of the sound determines which group of hair cell cilia are activated, whereby it becomes possible to distinguish between different sounds. If one’s hair cells are damaged due to age, illness or other causes, they will have problems hearing certain sounds and differentiating between sounds. Large amounts of ear wax can also considerably reduce the ability to hear.
SEE ALSO:
Hearing, a tour of the earInner earOuter earMiddle ear
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