Ear Anatomy |
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 The ear is separated into 3 regions: the outer, middle and inner ear. The outer ear includes the external ear (pinna), the ear canal and the ear drum (tympanic membrane). The middle ear is a space on the other side of the ear drum that contains the three smallest bones in the body: the hammer (malleus), anvil (incus) and stirrup (stapes). Together they form a chain that amplifies the sound waves that are vibrating the ear drum. The middle ear is a space - filled with air and lined with mucosa which moistens the space - similar to a sinus. The middle ear chamber is connected to the many air spaces in the surrounding bone (mastoid bone). In order to equalize the pressure between the outside air and the air containing middle ear space, there is a tube (eustachian tube) connecting the middle ear with the back of the nose. The inner ear is the site of the specialized nerves that allow us to hear and keep our balance. These two sets of nerves are divided into two structures, the cochlea (looks like a snail) and the labyrinth, also known as the vestibular system or semicircular canals (looks like a gyroscope). They share a complex pair of fluid-filled chambers. The specialized cochlear nerves (hearing) and vestibular nerves (balance) have microscopic hairs, or cilia, on their surface which are stimulated by movement of the fluid . The stapes is a piston that moves the fluid inside the cochlea and gravity moves the fluids in the semicircular canals. Sound entering the external ear travels as mechanical vibrations through the ear drum and the ear bones to the inner ear. The cochlea has 2 1/2 turns and contains 2 different fluid chambers. The vibration of the stapes sets in motion the fluid. Thirty thousand nerve endings (hair cells) sense this motion and convert this energy into electric impulses of one millionth of a volt. The nerve impulse is then sent to the brain where it is interpreted as sound. The other part of the inner ear is the vestibular semi-circular canals which help us to maintain our balance. The fluid within these canals flows back and forth to stimulate the vestibular nerve endings. These impulses are sent to the brain for interpretation. Our balance is maintained by the brain collecting the information from three sources: our two vestibular systems, our eyes and the pressure sensors of our joints and muscles, particularly under our feet. |
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| The inner ear structures: the snail-like cochlea (hearing) and the semi-circular canals with their specialized nerve endings inside the utricle and saccule |
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 The some of the 30,000 nerves with their clumps of white cilia, lined up in 4 distinct rows. This is microscopic and is magnified 1000 times for this image. mouseover to enlarge image |
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 Once the sound waves have moved the cilia of the cochlear nerves, those cells create a chemical change that is equivalent to an electrical signal that is passed from one connecting cell to another up into the brain. There are seven district clusters of nerve interconnections that occur before the information is relayed into our auditory cortex. mouseover to enlarge image |