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Hearing Loss >> The Hearing System
The Hearing System
All
sounds originate from movement. For example, when we speak the air
coming from our mouth pushes the molecules in the air, making them
vibrate. These vibrations are called
sound waves and can be perceived by the ear. Slow vibrations (low
frequency) are heard as deep tones (bass), while fast vibrations (high
frequency) are heard as high tone (treble).
The
complete hearing system is responsible for our sense of hearing. It
picks up mostly acoustic waves and transforms them into neural codes,
which can be interpreted by the brain.
(PICTURE)
How the ear
works?
The
ear consists of three main sections: the external ear, the middle ear
and the inner ear.
The outer
ear
The
outer ear is made up of the external cartilaginous part of the ear and
the canal. The eardrum is located at the end of the ear canal and forms
the boundary to the middle ear.
The outer ear picks up sound waves and directs the sound to the
eardrum. The sound wave pressure
causes the eardrum to vibrate and the middle ear comes into action.
The middle
ear
The
middle ear is a room filled with air. The Eustachian tube, which
connects the middle ear to the throat functions to keep the air
pressure in the middle ear equal to the external air pressure. There
are three tiny bones in the middle ear cavity commonly called the
hammer, the anvil and the stirrup. This chain of bones forms a lever
mechanism conducting movements of the eardrum to the fluids of the
inner ear.
Two
small muscles, the stapedius and the tensor
tympani are attached to the bones.
These muscles are activated by a reflex when loud sounds reach
the ear. This muscle reflex reduces excessive sound pressure before it
reaches the inner ear.
The inner
ear
The
inner ear or the cochlea is shaped like a snail and filled with fluid.
The oval window connects the middle ear and the inner ear. The base of
the stapes is attached to the oval window and functions as a piston
moving the fluid of the inner ear.
This
movement of the fluid activates the hair cells in the inner ear (there
are about 20000 of these sensory cells). When the hair cells are
activated, they send impulses via the auditory nerve to the brain,
which perceives these impulses as sound.
Via
these fantastic twisting ways the ear is able to pick up sound waves,
transform them to mechanical energy (ossicles)
then to hydraulic energy (wave movement in fluid) and finally to an
electrical energy (nerve impulses) that can be interpreted by the
brain. Even the slightest flaw in this complex system can compromise
hearing ability.
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