The Ear and Hearing Loss


The ear is the organ of hearing and balance in vertebrates. The ear
converts sound waves in the air, to nerve impulses which are sent to the brain,
where the brain interprets them as sounds instead of vibrations. The innermost
part of the ear maintains equilibrium or balance. The vestibular apparatus
contains semicircular canals which in turn balance you. Any movement by the
head, and this apparatus sends a signal to the brain so that your reflex action
is to move your foot to balance you.
The ear in humans consist three parts: The outer, the middle, and the
inner portions. The outer ear, or pinna, is the structure that we call the ear.
It is the skin covered flap of elastic cartilage, that sticks out from the side
of the head. It acts like a funnel catching sound and sending it to the middle
portion of the ear. The middle portion contains the ear drum and the connection
between the pharynx and the drum, the Eustachian tube. The inner ear contains
the sensory receptors for hearing which are enclosed in a fluid filled chamber
called the cochlea. The outer and middle ears purposes are only to receive and
amplify sound. Those parts ofd the ear are only present in amphibians and
mammals, but the inner ear is present in all vertebrates.
The ear can hear in several different ways. They are volume, pitch, and
tone. Pitch is related to the frequency of the sound wave. The volume depends
on the amplitude or intensity of the sound wave. The greater the frequency, the
higher the pitch. Humans can hear about 30 and 20,000 waves or cycles per
second. High pitch sounds produce more of a trebly sound, while low pitch
sounds produce a rumbling bass sound.
When a person loses these abilities to comprehend sound, it is referred
to as deafness. It can be caused by disease, toxic drugs, trauma, or an
inherited disorder. Those causes can be classified as conductive, sensorineural,
or both.
A conductive hearing loss results from damage to those parts of the ear
which transmit sound vibrations in the air to the fluids of the inner ear. This
type of damage is usually to the eardrum or small bones known as ossicles.
Ossicles conduct sound from the eardrum to the cochlea. They cannot perform
such an action if the eardrum is perforated, if the middle ear cavity is filled
with fluid, or if the bones become separated, are destroyed by disease, or are
overgrown by a spongy bone ( a disorder called otosclerosis). In conductive
hearing loss, sound intensity is reduced, but sound isn\'t distorted.
Sensorineural hearing loss is more resistant to therapy because it
involves damage to the delicate sensory cells of the organ of Corti, which is
located in the cochlea. Sensorineural hearing loss has to do with both
distortion of sound and loss of sound intensity. The closer the damaged tissue
is to the auditory cortex, the more complex and subtle are the types of
distortions. The hair cells of the organ of Corti cannot grow once they are
damaged. Sensorineural hearing loss is rarely reversible.
The hearing losses caused by salicylates such as asprin and the early
stages of Meniere\'s Disease are reversible, however. The latter condition is
characterized by an imbalance of fluid pressures within the inner ear. If this
imbalance is correct soon enough, before hair cell destruction has occurred,
hearing will return to its normal level. Sensorineural hearing loss is often
accompanied by ear noise, or tinnitus, which is a high-pitched ringing heard
only by the patient. Because the inner ear has no pain fibers, damage is not
accompanied by pain.
Hearing loss is usually measured by an instrument called an audiometer
which measures the weakest intensity at which a person can hear at most
frequencies in the range of human hearing. The instrument is calibrated against
the lowest intensity heard by normal humans at each frequency, according to an
international standard. Audiometry can determine the amount of hearing loss-
whether it is conductive or sensorineural in nature, and how much of each type
of damage has occurred.
Rehabilitation is available for patients with hearing losses. There are
lots of programs and resources for these people. Most are special schools. One
example might be Cleary\'s School for the Deaf. These schools try to provide an
environment that is as close to a normal classroom as possible. As a matter of
fact, sometimes they use regular classroom\'s but they provide special teaching
assistants to help individual student\'s.
The next step away from a normal classroom is the special