What causes hearing loss? Problems in the outer, middle, and inner ear
The Outer Ear • Anything that completely blocks the ear canal can cause hearing loss. • Blockage with earwax (also called cerumen) is common. • Infections with swelling that shuts the ear canal • Foreign bodies in the ear • An injury • Birth defects • A growth in the ear canal
How would an ear canal blockage cause hearing loss? • Any of these, including blockage by wax, may result in conductive hearing loss . • That is, it interferes with sound conduction and is generally correctable. • It causes decrease in volume but does not generally produce distortion.
The Middle Ear • Problems that can affect the middle ear and lead to hearing loss include: • Ear infections • Fluid in the ear • Otosclerosis • Birth defects • Tumors
Ear Infections & Fluid in the Ear • Middle ear infections cause swelling of the lining in the middle ear, and often an accumulation of fluid.
Fluid build-up is caused by a malfunction of the Eustachian tube, which connects the ear with the back of the throat. • The job of the Eustachian tube is to equalize the pressure in the middle ear. (It makes your ears “pop”)
Normal ear drum How would this cause hearing loss? Fluid behind the ear drum
It sometimes requires drainage through a myringotomy or with the placement of ear tubes .
Otosclerosis • A hereditary disease in which new bone is deposited around one of the tiny bones in the middle ear, specifically around the footplate of the stapes (or 'stirrup') bone. • How would this cause hearing loss?
The Inner Ear • There are many conditions that cause the delicate inner portion of the ear to function abnormally. • They include: • Otosclerosis • Presbycusis • Fistula • Head injury • Meniere's syndrome • Noise • Infections • Sudden deafness • Neural problems
Presbycusis • The natural aging process also causes sensorineural hearing loss. • the damage lies in the inner ear, the auditory nerve, or both. • Beginning shortly after birth, we begin to lose hair cells and nerve endings within the cochlea. • How would this cause hearing loss?
Noise • Noise is an important cause of hearing loss. • An estimated 7 to 10 million people in American industry have noise-induced hearing loss, virtually all of which was preventable. • In addition to industrial noise, recreational noise can damage hearing. • Such noise is encountered commonly from power tools, motorcycles, loud music (especially with earphones), etc.
Neural problems • Neural (nerve-related) problems may also produce hearing loss. Among the more common are: • Acoustic neuroma , a common tumor of the acoustic nerve • Multiple sclerosis • Autoimmune sensorineural hearing loss, in which the body attacks its own ear • Ototoxicity, which is hearing loss caused by a substance that gets into the body • most often the substance is a medication (antibiotic, etc.). How would this cause hearing loss?
Hearing Aids • Hearing aids are fairly simple devices, consisting of four basic parts: • A microphone picks up sound from the environment and converts it into an electrical signal, which it sends to the amplifier. • An amplifier increases the volume of the sound and sends it to the receiver. • A receiver/speaker changes the electrical signal back into sound and sends it into the ear. Then those impulses are sent to the brain. • A battery provides power to the hearing aid.
Hearing aids aren't effective for everyone. • WHY NOT? • Hair cells in the inner ear must pick up the vibrations that the hearing aid sends and convert those vibrations into nerve signals. • So, you need to have at least some hair cells in the inner ear for it to work. • And, even if some hair cells remain, a hearing aid won't completely restore normal hearing.
What can people with hearing aids hear? • http://www.utdallas.edu/~thib/fm_wav.html
Cochlear Implants • Cochlear implants work better in people with more severe ear damage because they bypass the damaged parts of the ear and send the sound information -- as electrical signals -- directly to the auditory nerve.
external system three parts a sound processor (2) a microphone (1) a transmitter (3) internal system two parts a receiver (5) an electrode array (6) The cochlear implant is made up of two main systems:
The microphone picks up sound and sends it to the sound processor, which translates sound into digital information. • It sends this digital information to the implanted receiver, which changes the digital information into electrical signals and sends these signals to the electrode array. • The electrode array sends these signals to the auditory nerve, which then passes along the signals to the brain.
The Cochlear Debate • Cochlear implants allow totally deaf people to hear common sounds such has a telephone, doorbell, car horn, and spoken voice. • In almost all people, understanding of speech is possible and lip reading is improved dramatically by the ability to hear the rhythms and the stops in normal speech. • Most people are able to talk on the telephone with modern cochlear implants.
However… • During the installation of a cochlear implant, all hair cells in the cochlea are destroyed. • Why is this a problem? • Damage of current hearing • Future technology
What can people with cochlear implants hear? • http://www.sens.com/helps/demo05/helps_d05a_demo_blank.htm • http://www.ucihs.uci.edu/hesp/Simulations/simulationsmain.htm