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Sound hits your ears in the form
of sound waves or vibrations traveling within the surrounding air.
The outer ear acts as a funnel for directing these vibration waves
into the ear canal. Ridges and hollows of your external ears vibrate
at different frequencies. Sensory nerves on the skin's surface
detect these differences, allowing the brain to determine where
a sound is coming from. The sound waves travel through the external
ear canal and pound against a .1 square inch membrane, called the tympanic membrane or ear
drum, causing it to vibrate. The vibrations across the entire membrane are
focused onto a single point where the malleus
attaches, thus amplifying the vibration. The malleus is one of three
oscillating bones called auditory ossicles,
the smallest bones in the body. The malleus oscillates like a teeter-totter
on its fulcrum made of a tiny ligament. The other end of the malleus
pushes against the next ossicle called the incus.
This also oscillates like a teeter-totter, only the end pushing
the next ossicle is much longer than the end attached to the malleus.
As a result the vibration is further amplified by about one third.
This longer end of the incus pushes on the final ossicle called
the stapes, which pushes against another
membrane called the foramen ovale or
oval window. This membrane is about one
two-hundredth of a square inch. Its surface is much smaller than
the ear drum, so a vibration of the ear drum results in a much more
concentrated vibration of the smaller oval window. This effect causes
another amplification of about 20 times. The opposite surface of
the oval window opens into a coiled structure shaped like a snail
shell, called the cochlea. The vibrations
travel through one of three fluid-filled tubes within the cochlea
until they reach the end (apex) of the coil. They then travel back
down the coil through another fluid filled tube until they are absorbed
by a third vibrating membrane called the round
window. Between these two tubes there exists a third inner
tube, the membrane of which houses about 15,500 sensory hair cells.
Vibrations traveling up the coil pass into the inner tube and cause
the hair cells to move, which sends a nerve impulse to the brain,
to be interpreted as sound. Vibrations traveling back down the coil
cause other hair cells to move producing more interpreted sound.
The more the hair cells move, the louder the sound is. The coil
vibrates differently along its length due to variances in flexibility.
High frequency vibrations cause it to vibrate more at its base,
while low frequency vibrations cause it to vibrate more near the
apex. As a result, hair cells in different locations pick up vibrations
of different frequencies allowing us to observe differences in pitch.
Balance is achieved by incorporating a mixture
of senses. You observe visual references, such as the horizon, with
your eyes. Your eyes as well as nerves from the muscles in your
body tell your brain what position you're in. Most importantly,
a tiny organ, called the vestibular organ,
embedded in each side of your skull within the inner ear, detects
the movement and direction of your head. This organ is composed
of tiny sacs and tubes. On the inner surface of each sac there's
a layer of jelly with tiny crystals lying on its surface. Sensory
nerves extend tiny hairs into the jelly. If the orientation of the
head changes or if the head is moved through space, then gravity
and other forces pull on the crystals thus causing the jelly to
move. To visualize this, imagine a bowl of Jell-O. If the bowl was
suddenly tipped or moved, the Jell-O might simply move with the
bowl. However, now imagine some heavy fruit placed on top of the
sticky Jell-O. This fruit represents the crystals lying on the jelly
in the vestibular organ. Now imagine the bowl being tipped or suddenly
moved. The surface of the Jell-O attached to the bowl will tend
to move with the bowl, while the surface of the Jell-O attached
to the fruit may be left slightly behind, due to the fruit's
inertia. As a result, the Jell-O will be stretched or sheared. The
same thing happens to the jelly within the vestibular organ. This
stretching or shearing of the jelly tugs on sensory hairs embedded
within the jelly. These sensory hairs send nerve impulses to the
brain, which are translated into observations of the movement, direction,
and orientation of your head. This information is constantly used
to retain your sense of balance. The vestibular organ is extremely
sensitive, detecting changes in position as little as a few hair
widths. During complex movements like those of competitive diving,
your body often tends to follow your head. Your head is also one
of the most vital parts of your body. Impact to your head can be
devastating. When avoiding a collision with an object, protecting
your head is more important than protecting most other parts of
your body. Thus knowing the specific location and orientation of
your head is more important than knowing the specific location of
other body parts. For these reasons, your vestibular organ has evolved
to be extremely sensitive and vital to your sense of balance.
Ear Piercing
Warning: If you're a heavy bleeder,
allergic to metals, have a weakened immune system, or easily form
scars, talk to your physician before piercing your body. If the
doc gives you the OK, have the physician do it.
Where to Pierce:
The ear lobe is the safest place to pierce your body. The rest of
the ear contains cartilage that doesn't heal as easily, and
is thus more vulnerable to infection.
Doing it Yourself:
Is not recommended. You are more vulnerable to infection and scarring,
if you have someone other than a professional do it. Also, if you
and your friend do it together and share a needle, you could transfer
blood born diseases.
The Safest Way to Pierce:
A physician will use a sterile, stainless-steel needle or a sterile,
stapler-like instrument. It will be virtually painless and the physician
may even use an anesthetic cream to ensure comfort during the piercing.
The Next Safest Way to Pierce:
Trained technicians in department stores or jewelry stores can pierce
the ear using the post of the earring. Make sure they sterilize
your ear before and after with alcohol, and make sure the earring
is sterilized and has never been used.
After the Piercing:
Surgical stainless-steel or 14 carat-gold studs are immediately
inserted and worn continuously for the next 6 weeks, until the ears
have completely healed. Throughout this time you should regularly
dab the ears with alcohol or mild soap. Don't remove or replace
the earrings until the ear has completely healed. Post earrings
are the best earrings to wear for the first 6 months, resulting
in a nice small round hole.
In space, gravity no longer pulls at the crystals
in the vestibular organ and normal horizons don't exist so the
brain's sense of balance becomes a bit numb. Eventually the
brain adapts to the new environment. Then when the astronauts return
to Earth, they acquire a sort of sea sickness; their brain, which
has adapted to life in space, must now readapt to life on Earth.
Until this readjustment occurs, they can feel disorientated and
nauseous for weeks.
Nervous
System
Brain
Eyes
Nose
Tongue
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