When someone refers to our “ears” or our sense of “hearing”, we often think of the visible portion of the ear, also known as the pinna (or auricle). However, the ear is much more complicated than the visible portion alone, although the outer ear is extremely important in and of itself. The pinna is shaped in such a way to funnel exterior sound waves and send them travelling through the ear canal (also known as the external auditory canal or external auditory meatus) and towards the eardrum (also known as the tympanic membrane).
When the sound waves reach the eardrum, the eardrum starts to vibrate. The vibrations pass through three tiny bones (or ossicles) known as the malleus, incus and stapes (also called the hammer, the anvil and the stirrup). These are actually the smallest bones in our bodies!
These tiny bones are part of the “middle ear”, which is an air-filled space. The middle ear also contains the Eustachian tube, which functions to regulate air pressure within the middle ear space and to drain excess fluid that may accumulate in the middle ear. Many people have felt the Eustachian tube working when they can feel their ears popping after getting off an airplane or when recovering from a cold. The ears suddenly feel clear again, and this is an example of the Eustachian tube at work.
When the eardrum vibrates, the middle ear bones move back and forth mechanically. This back and forth motion causes the footplate of the stapes to literally push itself into the oval window of the snail-shaped cochlea (in the inner ear). The cochlea is fluid-filled and is lined with cells that have thousands of tiny hairs on their surface. When the footplate of the stapes pushes into the oval window of the cochlea, it causes the fluid to move across the tiny hair cells.
The movement of these hair cells causes neurotransmitter to be released. This stimulates the nerve fibres that send electrical signals along the auditory nerve, and ultimately to the brain where we process it as “sound”. Different areas of the cochlea are stimulated depending on the pitch (or frequency) of the sounds that enter it. For example, high frequency (high-pitched) sounds are registered at the base of the cochlea, because low-frequency (low pitched, bass-type) sounds are registered at the apex of the cochlea.
Ultimately, we hear with our brains! Any defects, damage, infections etc along the hearing pathway (this can be in the outer ear, middle ear, inner ear, or auditory nerve) will inhibit sound from getting to our brains, and this is how hearing loss occurs. Some problems along the pathway are correctable, and some problems are permanent. The treatments available are solely dependent on the type of hearing loss a person has (where the problem area is located) as well as the degree of loss (how significant the loss is, which can range from mild to profound and can vary for different pitches).