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What is hearing loss?
About
the ear
How do we hear?
How
Does Hearing Loss Affect One's Life? What
is Hearing Loss?
Hearing loss, or deafness, is the partial or total inability
to hear sound in one or both ears.
The human ear is amazing. It is one of the smallest and most complex
organs in the body, capable of turning the tiniest disturbances
in air molecules into a form the brain can understand - and doing
so instantaneously, over an enormous range of pitch and loudness.
Considering the ear's delicacy, it is remarkably resilient. Nevertheless,
illness or injury can impair our ability to hear properly.
In recent years, substantial advances have made it possible to
determine the cause of hearing impairment in nearly all cases,
and to treat the hearing loss in many ears.
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About the Ear
The ear is divided into three major parts:
- The outer ear
- The middle ear
- The inner ear
The outer ear has two parts:
- The trumpet-shaped, protruding part of the ear on each side
of the head, called the auricle or pinna
- The tube leading into the ear, called the auditory canal;
the opening is called the meatus
In the middle ear:
The eardrum (tympanic membrane) stretches across the inner
end of the auditory canal.
The middle-ear chamber is filled with air. There is an opening
from the middle ear to the throat through a tube called the
Eustachian
tube. The Eustachian tube helps to equalize pressure on both
sides of the eardrum.
A chain of three small bones, called Ossicles, connects
the eardrum to the inner ear. These bones are named for their
shapes: the hammer, anvil, and stirrup.
The inner ear is a fluid-filled chamber divided into two
parts:
- The vestibular labyrinth, which is the portion of the
inner ear that functions as part of the body's balance mechanism
- The cochlea, which contains the hearing-sensing nerve
The cochlea is a hollow tube inside the inner ear that is coiled
to resemble a snail's shell. It contains thin fluid and a highly
specialized structure called the organ of Corti, which contains
thousands of minute, sensory, hair-like cells. The organ of Corti
functions as the switchboard of the hearing system.
It is to the cochlea that sound vibrations picked up by the middle
ear are carried.
The acoustic nerve (also called the eighth cranial or auditory nerve)
leads from the inner ear to the brain, serving as the pathway for
the nerve impulses that the brain will interpret as sound.
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How Do We Hear?
Hearing involves a complex chain reaction within the ear:
- Sound creates vibrations in the air somewhat similar to the
rippling waves created when a stone is thrown into a pond
- The outer-ear "trumpet" collects these sound waves,
and they are funnelled down the external ear canal to the eardrum
- As the sound waves strike the eardrum, they cause it to vibrate
- The vibrations are transmitted through the middle ear over
the bony bridge formed by the hammer, anvil, and stirrup
- These vibrations, in turn, cause the membranes over the openings
to the inner ear to vibrate, causing the fluid in the inner
ear to be set in motion
- The motion of the fluid in the inner ear excites the nerve
cells in the organ of Corti, producing electrochemical impulses
that are gathered together and transmitted to the brain along
the acoustic nerve.
- As the impulses reach the brain, we experience the sensation
of hearing
- The inner ear
The sensitivity of the hearing mechanism is most extraordinary.
With the softest detectable sound, the eardrum only moves approximately
one-millionth of an inch. Our ability to detect sounds from the
softest to the loudest covers an intensity range of approximately
100,000,000 to 1.
What we hear are sound waves provided by vibrations of air molecules.
The size and energy of these waves determine the loudness, which
is measured in decibels (db). The number of vibrations or cycles
per second makes up frequency - the more vibrations, the higher
the pitch of the sound. Sound frequency is expressed in cycles per
second, or hertz (Hz).
Many young, healthy humans (through teens and early twenties) can
hear frequencies from about 20 Hz to 20,000 Hz, and can detect frequency
differences as small as 0.2%. That is, we can tell the difference
between a sound of 1000 Hz, and one of 1002 Hz.
Consequently, it is no surprise that such a remarkably complex system
can be damaged by various illnesses and injuries.
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How Does Hearing Loss Affect One's Life?
Virtually no condition in medicine can have as profound an effect
on quality of life as even moderate hearing loss in some people.
Hearing loss makes even routine communication difficult. High
frequency hearing loss often involves loss of ability to hear
consonants such as s, f, t, and z, even though vowels can be heard
normally. Consequently, people hear but cannot make out what is
being said.
This may result in frustration, withdrawal from social activities,
depression, and marital discord. People lose the ability to take
in the sounds like bird songs, rustling of leaves, and the voices
of children. In general, these infringements on the quality of
life can be overcome through medical or surgical treatment or
with hearing aids.
When hearing loss occurs early in childhood, its devastating consequences
are more obvious than when it occurs late in life. A hearing deficit
in infants can interfere with psychological, emotional, and speech
development. It also makes learning a mammoth task and can cause
frustration or isolation.
Even more mild forms of hearing loss early in life can cause great
difficulties, including poor attention and bad grades in school.
Frequently, such children are considered "not too bright,"
before anyone realises that a hearing loss is present. When it
is corrected, the changes in the child's performance, attitude,
and interactions are often remarkable.
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