Hearing: The Basics
The process of hearing seems simple enough on the surface: we hear a sound, we recognize the sound, and we react to the sound. In reality, however, hearing is a complex process that requires the coordination of a number of different body parts and functions. To hear well, sound must travel through the outer ear, to the middle ear, and then to the inner ear, where it is converted into signals that are detected and decoded by the brain. How does all this happen?
Sound first touches the outer ear, which consists of the pinna (the part of the ear that we all see and recognize) and the ear canal (the part of the ear that likes to gather ear wax). The pinna (the part of the ear you see) is shaped in a way that helps us recognize where sound comes from. Sound enters the pinna and is then routed to the ear canal. The ear canal funnels sound down to the middle ear, which starts with the ear drum. The ear drum, also called the tympanic membrane, is at the end of the ear canal and functions just like its name suggests- when it is hit with sound, it vibrates like a drum. On the other side of the ear drum are three tiny bones, called ossicles. There are three ossicles- the malleus, the incus, and the stapes. When the ear drum vibrates, it makes these tiny bones move as well. As they do, they hit another membrane, further inside the ear, called the oval window. (Are you amazed that you are able to hear yet? Keep reading!)
Once the sound reaches the membrane called the oval window, it has reached the inner ear. The inner ear is made up of a snail shaped bony structure called the cochlea. The cochlea is filled with fluid. When the ossicles (the tiny bones in the middle ear) hit the oval window (the membrane at the end of the middle ear), the movement of the oval window makes the fluid in the cochlea move. This, in turn, stimulates tiny hair cells that are also in the cochlea. There are certain hairs cells that are activated depending on the pitch (or frequency) of the sound that is coming into the ear. Signals from the hair cells are translated into nerve impulses, which is code that the brain can make sense of. The signals move from the cochlea to the brain along the auditory nerve; if all goes well, the brain then processes the nerve impulses into sound that we can recognize.
When Things Go Wrong
With such a complex system in place, it can be easy to see how things might go wrong. And indeed, they sometimes do. There are a number of ways in which things can go awry in the hearing process, and when they do, the result is hearing loss. The type of hearing loss depends on what exactly has gone amiss in the process of hearing.
A conductive hearing loss occurs when there is some type of difficulty with the way that sound is processed through the outer ear (the ear lobe and the ear canal) or the middle ear (the ear drum or the ossicles). This type of hearing loss is often temporarily caused by ear infections: the fluid in the ear from ear infections prevents the ear drum from vibrating like it should, leading to difficulty hearing. Conductive hearing losses can be caused by a number of other of factors as well: ear wax, foreign bodies in the ear canal, or outer/middle ear structures that aren’t formed just as they should be. The good news is that many types of conductive hearing losses can be fixed through surgery or medication (for example, to clear the ear infection). Once fixed, hearing is restored.
A sensorineural hearing loss, on the other hand, is a result of a problem with one of two things: the inner ear which functions to process the sound in the cochlea or the auditory nerve which takes the sound from the cochlea to the brain. This type of hearing loss can’t be fixed with surgery or medication and is caused by things such as illness, age, genetics, head trauma, or consistent exposure to loud noise. Some select people with significant sensorineural hearing loss in both ears will be able to receive a cochlear implant, which is a device that is implanted inside the ear and acts like the cochlea, transmitting sound by directly stimulating the auditory nerve. Finally, some people have a mixed hearing loss, meaning that their hearing loss is due to difficulty with both the outer/middle ear and inner ear/auditory nerve.
Audiologists are professionals who help diagnose and treat people who have a hearing loss. If you have concerns about a possible hearing loss, don’t hesitate to contact your physician, who may screen your hearing and/or make a referral to an audiologist. Only audiologists can fully assess the type and extent of hearing loss and help you make a plan for treatment options.