Ears

inner earEars

Your ears provide your sense of hearing as well as your sense of movement, direction and balance.

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Good Vibrations: From the Air to your Inner Ear

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 Ossicles: Tympanic Membrane to Oval Window

The vibrations across the tympanic 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.

Cochlea

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: The Vestibular Organ

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.

User's Manual

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.

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Amazing Facts

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.

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