Components of the Ear
- The ear or pinna
- The ear canal
The ear drum
The three (3) small bones:
- Hammer (malleus)
- Anvil (incus)
- Stirrup (stapes)
- Semicircular Balance Canals
- Auditory nerve
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How We Hear
- Sound waves enter the ear canal and hit the ear drum
- From the ear drum, sound is passed through the three (3) middle ear bones
- The stapes sends the vibration to the fluids inside the cochlea
- The vibration in the fluids make the hair cells move
- The hair cells correspond to the frequency of the original sound waves and initiate electrical signals in their corresponding nerve endings
- The electrical signals are sent to the brain through the auditory nerve
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.
- Usually involves a reduction in sound level, or the ability to hear faint sounds.
- Usually mild or moderate hearing loss
- Can be temporary in some cases
- Can usually be medically or surgically corrected
- Can be caused by obstruction of the ear canal, infections or fluid in the middle ear space, perforations of the ear drum, and the abnormalities of the middle ear hearing bones.
Sensorineural Hearing Loss
- Occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain
- Involves a reduction in sound level, or ability to hear faint sounds and affects the ability to understand speech or hear clearly
- Can be caused by diseases, birth injury, drugs that are toxic to the auditory system, and genetic syndromes
- May also occur as a result of noise exposure, viruses, head trauma, aging, and tumors
- May be mild, moderate, severe, profound or total hearing loss
- Cannot be corrected medically or surgically. It is a permanent loss
- Treatment includes hearing aids or a cochlear implant
Auditory neuropathy is not a type of hearing loss but a dysfunction in the hearing system in which the auditory nerves do not respond to sound in a coordinated fashion.
Symptoms seen in auditory neuropathy include the following:
- Hearing test suggests a mild to moderate hearing loss
- Absent acoustic reflexes
- Absent or severely abnormal auditory brainstem responses
- Word recognition ability poorer than expected for the amount of pure tone hearing loss
- However, a major distinguishing feature is that in these patients otoacoustic emissions are present suggesting near normal cochlea function.
In auditory neuropathy the cochlea hair cells are responding to sound, but the auditory nerve does not transmit the signals to the brain in a coordinated, useful fashion. Since the cochlea is working in these patients a hearing aid is not appropriate since the ear does not need more volume of sound. In severe cases of auditory neuropathy a cochlear implant can be effective in synchronizing the auditory signal.