Many trivia questions about the smallest bones in the human body have brought fame to the malleus, the incus and the stapes (also known by their shapes as the hammer, anvil and stirrup). Just inches inside the ear, these three tiny connected bones, together called the ossicles (http://subent.com/images/ossicles.jpg), give movement to the sounds we hear, all in an instant.
Sounds are waves that vibrate the eardrum (tympanic membrane) that then make these bones quiver. That movement sends waves of vibrations into a pool of liquid (the cochlea) that is lined with thousands of hair cells (the organ of Corti). Those hair cells communicate with the brain to determine the sound's loudness, pitch and quality, all in a space the size of a pencil eraser. And that's just the beginning ...
Catch the wave. The part of the ear we can see and pull on is the pinna. The shape and curves are designed to capture sound waves from various directions and funnel them into the ear to start vibrating those ossicles. Cupping your hand behind the ear and pulling it forward makes sounds louder because your hand is snagging more sound waves.
Selective hearing. The brain is constantly making decisions on what to hear and what not to hear. When everything works correctly, we can reject all the hubbub at a party and zero in on one particular voice. At a musical performance, we can choose to single out the sounds of one instrument in the midst of an orchestra. This sense of hearing discrimination is poorly understood, but often diminishes as we age. Some call this the "cocktail party problem (http://www.nbcnews.com/id/28423422/ns/health-health_care/t/cant-hear-holiday-parties-blame-your-brain/#.UaayBtLVCSo)." One obvious fix is to move your conversation away from the crowd.
Hearing the high notes. The higher the pitch, the faster the sound wave vibrates. Over time, that can overwork and damage those hair cells. Sometimes that shows up when we think people around us are mumbling. Our ability to distinguish consonant sounds is related to those higher pitches. For example, "What time is it?" and "What kind is it?" sound the same to those who have lost the function of some of those hair cells.
Ears never sleep. Even when we're asleep, our hearing continues to screen sounds efficiently. The brain can decide when to ignore noisy traffic and trains, yet promptly wake you with the ding of the alarm clock. So when dad sleeps through the crying baby and mom is up all night, it's likely because the brain has decided to filter those sounds differently.
Saved by the smallest muscle. In addition to holding the smallest bones, the ear claims the prize for the smallest skeletal muscle, the stapedius. This muscle can pull back the stapes, dampening a sound vibration to protect the inner ear from loud noises. Along with another muscle (the tensor tympani) it works every time we speak. Otherwise, the sound of our own voice would reverberate inside our heads. If we know a loud noise is coming, we subconsciously activate the stapedius (making firecrackers more tolerable).
Don't miss a sound. Ears are amazing, and we can expect them to handle all this and more. But if you think yours aren't working up to par, see your health care provider.
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