Feb 20, 2007
2:00/1:00 MT/PT
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Hearing Facts Title

     Outer earHearing is one of our five senses. Hearing and the other four senses: seeing, tasting, smelling and touching, all play an important part in our understanding of the world around us. What is hearing? Your ears are in charge of collecting sounds, processing them, and sending sound signals to your brain. The brain interprets the sounds

How do we hear?
     Hearing happens when the ear changes sound waves into electrical signals thatThe brainare sent to the brain. We don't really hear with our ears ...we hear with our brains!!!

Let's look at how the ear is put together ( Scientists call this "anatomy")

The ear has three main parts: the outer, middle, and inner ear.
Use your brain as you watch this animated demonstration from KidsHealth: How the Ear Works.

PinnaSound waves enter through the outer ear which is also called the "pinna". That's the part of the ear that we can see.

     From here the sound moves through the external auditory canal to the middle ear where they cause the eardrum to vibrate (move back and forth). Another name for the eardrum is " the tympanic membrane".
     The middle ear also has three tiny bones called the ossicles. These three bones are named the malleus, incus, and stapes (and are also known as the hammer, anvil, and stirrup). The eardrum and ossicles make the vibrations larger and carry them to the inner ear.

     The cochlea is a a snail-shaped, fluid filled structure in the inner ear. Inside the cochlea are tiny hair-like bundles. The inner ear changes the vibrations into nerve impulses which are sent to the brain along the auditory nerve.      Different sounds move the hair bundles in different ways. This helps the brain to tell one sound from another.
     In this photo, the bony wall of the cochlea has been cut away revealing the fluid filled spiral chambers within. You can see the stapes in the lower left. From the Auditory Science Lab at The Hospital for Sick Children
FACT: the stapes is the smallest bone in the human body. It is only 0.25 to 0.33 cm long [0.10 to 0.13 inches] and weighs only 1.9 to 4.3 milligrams.)
Image of the ear

Click on this image to see a
bigger image with labels of the anatomy of the ear .
Now you are ready to watch this video of how you hear!!
There are other important structures in the inner ear? They are called the semi-circular canals and they have nothing to do with our hearing. However they are very important with helping us to balance

We have 2 ears to help us locate a sound.Why do we have 2 ears?

     Two ears located on the sides of our heads allows us to locate the source of a sound. Try closing your eyes and have someone clap his hands. You will be able to point at that person because your brain is able to compute how much time went by between when your left ear heard the sound and when your right ear heard the sound. This can work because sound moves through air pretty slowly. It reaches one ear before the other and your amazing brain can use that information to help you locate the sound!!!

Let's look at SOUND WAVES:
Sound waves have two parts that are both important for our hearing: Frequency and Amplitude

1. Frequency (measured in cycles per second or cps, also called called Hertz (Hz) ) . Elephant EarsHumans can hear sounds waves with frequencies between 20 and 20,000 Hz.
Compare the frequencies that different animals can hear...notice how high a sound a bat can hear. Learn more about bats.

A hand cupping an earThe frog has an eardrum on the outside of of its body behind the eye??

2. Amplitude (measured in decibels or dB, named after Alexander Graham Bell)

     The loudness, or amplitude, of sound is measured in units called decibels (dB). This is the force of sound waves against the ear. The louder the sound, the more decibels

     Sounds we can hear can be very faint (like a whisper 30 dB) to very loud like a siren or jet engine (130dB). Long exposure to any noise above 90 decibels can cause gradual hearing loss.
      How does this happen? It has to do with the hair cells. Loud sounds and some infections can cause some of the hair cells to die. Once a hair cell dies it cannot grow back.

Protective EarphonesWe are born with only about 3500 of these hairs so make sure you protect your hearing from loud noises. You can read about this in an article from the Center for Disease Control called Noise: The Invisible Hazard.

Examine this list of noises which can damage your hearing. Wear ear plugs when you are involved in a loud activity.

Here's your last chance to read about the the pathway sound takes from your outer ear to your brain... but I bet you already know how it happens!!
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