A critical portion of the information we gain each day is through our ears. Many structures work together to properly convey sound waves to the hearing center in the brain to provide accurate hearing. A problem with any one of these structures can result in hearing impairment, while in severe cases, such problems can cause deafness.
Auricle and Ear Canal
Sound waves that get to the ear must be collected and rerouted in the right direction. This is done by the auricle -- the external part of the ear -- which acts as a funnel, sending the waves into the ear canal, which leads to the eardrum. Any interruption in this route may cause a certain degree of hearing impairment.
The eardrum transmits the sound waves from the air to the small bones behind the eardrum, and from there to the cochlea, which is filled with fluid. In other words, the eardrum helps in the conversion and amplification of sound waves as they travel from air to liquid. A tear in the eardrum can occur as a result of injury, infection or playing certain sports. Although hearing ability is typically impaired for a while, the tear usually heals itself within a few weeks.
After leaving the eardrum, the sound waves travel to three small bones, known as ossicles, the smallest bones in the body. They form small joints with each other and function like levers -- their small size focuses the vibrations and tends to amplify them as they move to the oval window of the cochlea. Anything that hinders the movement of these bones will tend to impair your hearing.
The cochlea is a coiled structure about the size of a pea, similar in appearance to the spiral shell of a snail. All mechanical waves entering this structure are converted into nerve impulses by highly specialized cells, known as hair cells. They are then transmitted to the brain via the auditory nerve. Damage to the hair cells results in hearing loss, which cannot be repaired. Some types of deafness can be treated with cochlear implants, which send signals to your auditory nerve, much as your own cochlea would do.
The activity of the hair cells sends messages along the auditory nerve, and from there to the hearing center of the brain, where hearing finally occurs. Your brain recognizes the type of sound, whether a fire alarm or your best friend's voice -- the location and type of the sound, whether near or far, loud or soft -- and sends messages to other parts of your brain that determine how you will respond to what you hear.