To help you understand the different types of hearing losses, it first helps to know about how the hearing system normally works.
The anatomy of the ear is described by three main sections: the outer ear, the middle ear and the inner ear. The outer ear includes the fleshy parts visible on the sides of the head, as well as the ear canal, which ends at the eardrum (waxed paper-like tympanic membrane.) The middle ear section lies behind the eardrum and includes a chain of three tiny middle ear bones (ossicles.) The inner ear lies deeper in the skull and includes the cochlea and the semicircular canals. Within the cochlea are special sensory cells (called hair cells, because of their appearance) that help decipher the specific pitches sent into the ear.
Normally, sound waves travel down the ear canal, transmit through the middle ear and then are sent to the inner ear, which next sends impulse signals via the auditory nerve to the brain for “processing” (interpretation) of those sounds. If any of the components are not working properly, the ability to hear well hearing can be compromised.
The Audiologist performs a diagnostic hearing evaluation to assess how well each component of the hearing system is functioning. If hearing loss is detected, it is categorized according to the part of the system that is not working correctly.
- Conductive Hearing Loss occurs when sound doesn’t travel through the eardrum and/or chain of tiny bones (ossicles) normally. Typically something is blocking sound transmission, reducing its loudness and intensity. A person with a conductive hearing loss hears all sounds at a reduced level and may be unable to detect faint sounds.
- Sensorineural Hearing Loss occurs when either the tiny hairs cells in the cochlea or the auditory nerve become damaged. (Such damage is typically a result of disease, injury from noise, normal aging process, or certain medicines.) Since the human body can’t regenerate sensory hair cells, once they are damaged, the hearing loss permanent. A person with this type of hearing loss may be unable to hear faint sounds and are likely to find that even when speech or other sounds are made loud enough to hear, they can still sound unclear or muffled.
- Mixed Hearing Loss indicates that both of the previous conditions are present.
- Central Hearing Loss occurs when the brain can no longer interpret sounds normally.