Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 04 table of contents.
Sound is initially collected by the outer ear, also called the auricle or pinna. This is the visible, fleshy part of the ear. The outer ear is shaped like a funnel, which helps it collect sound.
What is the auricle or pinna?
The human ear in cross-section
What is the tympanic membrane? What are the ossicles?
Sound enters the outer ear and travels down the auditory canal to the eardrum, which is also called the tympanic membrane. The tympanic membrane is the boundary between the outer and middle ear. Beyond the eardrum is the middle ear.
Within the middle ear are three tiny bones called ossicles, arranged in a chain. The ossicles consist of the hammer (malleus), anvil (incus), and stirrup (stapes, pronounced STAY-peez). The ossicles increase the force of vibrations of the tympanic membrane 20-30 times before passing them on to the inner ear. Therefore the middle ear is an amplifying system.
Enlarged view of the ossicles
What is the function of the Eustachian tube?
In order for the eardrum to move freely and painlessly, the air pressure inside the middle ear should be the same as it is outside. This is accomplished naturally in the body by venting the middle ear to the outside world through a small tube, the Eustachian tube, which runs from the middle ear to the back of the throat. The Eustachian tube (technically known as the pharyngotympanic or auditory tube) opens to equalize middle ear pressure each time you swallow. If you blow too hard on a balloon, the pressure will sometimes go up your Eustachian tube and cause pain in the middle ear.
Why do your ears feel funny when you drive up a mountain road?
Sometimes you need to equalize the pressure in the middle ear but the Eustachian tube stubbornly refuses to open. This causes a feeling of pressure in the ears. For example, if you ride a car up a mountain road, the air pressure outside drops and your eardrum bulges outward. Your ears feel funny, as though stuffed with cotton. To "clear your ears" you must open the Eustachian tube by chewing gum or yawning. Unfortunately, it is difficult to produce a real yawn when you need one, and deliberate yawning movements often will not work! When a genuine yawn occurs, the tube opens and the pressure equalizes, sometimes with a little popping sound.
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