How Hearing Works

Types of Hearing Loss

Conductive Hearing Loss occurs when sound is not conducted efficiently through the outer and middle ears, including the ear canal, eardrum, and the tiny bones, or ossicles, of the middle ear. Conductive hearing loss usually involves a reduction in sound level, or the ability to hear faint sounds. This type of hearing loss can often be corrected through medicine or surgery.

Sensorineural Hearing Loss occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear (retrocochlear pathway of the acoustic nerve) to the brain.

Sensorineural hearing loss not only involves a reduction in sound level, or ability to hear faint sounds, but also affects speech understanding or ability to hear clearly.

Central Auditory Processing Disorders
A central auditory processing disorder (CAPD) occurs when auditory centers of the brain are affected by injury, disease, tumor, heredity or unknown causes. CAPD does not necessarily involve (although it may) hearing loss. Central auditory processing involves sound localization and lateralization, auditory discrimination, auditory pattern recognition, the temporal aspects of sounds, and the ability to deal with degraded and competing acoustic signals. Therefore, a deficiency in one or more of the above listed behaviors may constitute a central auditory processing disorder. CAPD is often associated with Attention Deficit Disorder (ADD) or Attention Deficit Hyperactivity Disorder (ADHD).

Preventing Noise-Induced Hearing Loss

Noise-induced hearing loss can result from a single loud noise such as a firecracker or gunshot. Hearing loss can also result from prolonged exposure to noise over a period of time. It occurs gradually and painlessly. The best way to prevent noise-induced hearing loss is to take care of your hearing by protecting your ears from loud sounds.

We should not be exposed to 90 decibels (dB) of sound for longer than eight hours a day. For every 5 dB increase in volume, the maximum recommended exposure time is cut in half. Here are some examples of sound represented in decibels:

• As you can see, there are many everyday sounds that can cause noise-induced hearing loss. Here are some simple things you can do to protect your hearing: Wear earplugs when you’re exposed to loud noise at work or play.
• Pay attention to the noises around you. Turn down the volume on radios, TVs and stereos when you can. Whenever possible, leave noisy environments.
• Alternate a noisy activity with a quiet one to give your ears a rest.

The Outer Ear
The part of the outer ear that we see is called the pinna, or auricle. The pinna provides a natural boost for sounds in the 2000 to 3000 Hz frequency range. The ear canal, also called the external auditory meatus, is the other important outer ear landmark. The ear canal is lined with only a few layers of skin and it is a highly vascularized area. This means that there is an abundant flow of blood to the ear canal.

The Middle Ear
The eardrum, or tympanic membrane (abbreviated TM) is the dividing line between the outer and middle ears. The ossicles are the three tiny bones of the middle ear that are fully developed at birth. They serve as a mechanical link between the tympanic membrane and the inner ear. The Eustachian tube is the middle ear's air pressure equalizing system. The middle ear is encased in bone and does not communicate with the outside atmosphere except through the Eustachian tube.

The Inner Ear
The inner ear is a series of channels and chambers embedded deep within the temporal bone. The inner ear is called the cochlea. The cochlea transduces (changes from one form to another) the mechanical stimulus of sound, via the tympanic membrane and the ossicular chain, into a sequence of electrical discharges that is the language of the auditory nervous system.