Slide show: How you hear

Your ears are pretty amazing acoustic devices, as yet unmatched by human ingenuity. In a person with normal hearing, the ears — in combination with the brain — gather and interpret sounds. Your ears allow you to hear the voice of a loved one, the call of a songbird or a crack of thunder.

Many factors are involved in this sensory wonder, so take a look at some of the important structures that make up the ear.

The flap of skin, which covers cartilage on each side of your head, is the most visible and recognizable structure of the ear. But that's only one part. There are actually three complex, interconnected portions: the outer ear, middle ear and inner ear. Each plays an important role in hearing.

The outer ear is the part visible on each side of your head. It's made up of folds of skin and cartilage, called the pinna (PIN-uh), and the ear canal. The cup-like shape of the pinna gathers sound waves from the environment and directs them into the ear canal. The ear canal is an inch-long passageway that leads to the eardrum (tympanic membrane). When a sound wave travels through the ear canal, it strikes the taut membrane of the eardrum, causing the eardrum to vibrate.

The middle ear is an air-filled cavity between the eardrum and inner ear. It's connected to the back of your nose and upper part of your throat by a narrow channel called the auditory tube (eustachian tube). This tube normally remains closed until you swallow or yawn. Then it opens briefly to equalize air pressure within your middle ear to the air pressure outside. Equal pressure on both sides of the eardrum allows the membrane to vibrate normally.

The middle ear cavity contains three tiny bones — the hammer, anvil and stirrup — named for their corresponding shape. The hammer attaches to the lining of your eardrum, the anvil attaches to the hammer, and the stirrup links the anvil to the oval window ? the entrance of your inner ear.

When sound waves travel through the ear canal, the vibration of your eardrum causes these bones to vibrate. They work together like tiny levers to increase the sound level that reaches the inner ear. Because the eardrum is much larger than the oval window, the vibrations arrive at the inner ear with increased force.

The inner ear contains two of the most intricate parts of the hearing mechanism: the cochlea and vestibular labyrinth. The fluid-filled, snail-shaped cochlea (KOK-le-uh) — which is no larger than a pea — begins at the oval window. Sound vibrations from the oval window travel into the fluid of the cochlea, where tiny specialized cells convert the vibrations into electrical impulses. The auditory nerve transmits these impulses to your brain.

The vestibular labyrinth consists of three semicircular tubes that connect to one another and control your sense of balance. These canals contain fluid and cells sensitive to fluid movement. The cells track your body's movement so that you're aware of where your head is in relation to the world around you.

Electrical impulses travel through the auditory nerve to various information processing centers within your brain. These stations process the sounds to determine their origin. The impulses end in the auditory cortex within the temporal lobe. There, the brain sorts, processes and files information about the sound.

You have an auditory cortex within the temporal lobe on each side of your brain. Signals travel between the right and left temporal lobes. The comparisons and analyses of these signals help suppress background noise and allow you to focus on the sounds you want to hear.