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Transcript of Audiology
Auditory Nerve Let's start with... Pinna Concha Ear Canal External Auditory Meatus What does the Pinna do? funnel sound waves to the concha and the ear canal. It aids in localization of sound. It aids in the protection of the canal from foreign objects and trauma. What does the Concha do? Amplifies sound What does the ear canal do? Primary Function is amplification but it also has oil glands in outer 1/3 of canal. The cerumen (wax) serves as protection and lubrication. The scent of the wax serves as an insect repellant. The hair follicles help reduce dust and wax build-up. The lower portion of the ear drum (75%) is tightly stretched. The top portion (25%) is loose and floppy. This allows it to vibrate like a drum. Malleus, Incus, and Stapes, the bones in the middle ear, form the ossicular chain. These are the smallest bones in your body! (And yes, they can break.) These bones are held in place by 2 muscles. These muscles protect the ear from loud sounds.
Normally, they are relaxed. If the intensity of a sound is too great, then the muscles contract and they keep the muscles from vibrating so the sound doesn't get into the inner ear. The Eustacian Tube connects your middle ear to your throat. When it is open, it drains fluid out of your ear to prevent infections. It also helps the pressure in your middle ear match the pressure of your surroundings. The semicircular canals are responsible for your rotational balance. The cochlea is very complex! Basically, it has 24,000 hair cells that help us hear. There are two types of hair cells: inner and outer. The inner hair cells transmit electrical changes to the brain. The outer hair cells are used by the brain to send messages back to the cochlea. OK, so we know all the parts. Now how do we hear? The Auditory Nerve is the pathway for the electrical changes to and from the brain. Each of these hair cells corresponds to a certain frequency. When you listen to loud sounds for a long period of time, these hair cells die off. Once they are dead, they are dead. The cochlea is full of liquid that helps these hairs move and become stimulated when we hear a sound. http://www.youtube.com/watch?v=stiPMLtjYAw Causes of Deafness There are HUNDREDS of causes of deafness, but we will focus on a few. Presbycusis More common in men than women Hearing loss that happens naturally with old age Hair cells are damaged Becomes hard to hear and distinguish high pitch sounds Hearing aids may help Medications and Diseases Over 100 prescription and over the counter medications have been labeled "ototoxic". Aspirin and aspirin-containing drugs
Toxic affects appear to be dose related
hearing returns when you stop using the drug Drugs used during Chemotherapy
Effects on hearing can be minimized by monitoring blood levels Antibiotics
Ear drops containing certain antibiotics are not ototoxic UNLESS your ear drum is perforated
Hearing loss is usually permanent Non-steriodal anti-inflammatory Drugs
includes ibuprofen (Advil, Motrin, etc)
ototoxic effect is dose related and hearing almost always returns when you stop using them Diseases that can cause deafness if left untreated:
Syphilis Otitis Media – infection in the middle ear
Common in children
Eustachian tube is more horizontal than vertical
hearing loss can be permanent if left untreated External Otitis - infection of the outer ear
Common in adults
sometimes called “swimmer’s ear”
can be caused by bacteria, fungus, eczema, allergies, swimming, or irritation from scratching Acoustic Trauma - exposed to loud sounds Acoustic Trauma can also occur with a sudden loud sound, like an explosion. Physical trauma - those who suffer a head injury are more prone to hearing loss Tinnitus - Ringing in the ears
exact cause is unknown
thought to be damage to hair cells in the cochlea
the brain compensates for the damaged hair cell by creating its own noise Congenital vs. Acquired Deafness Born deaf Became deaf later in life All the causes of deafness we have discussed are acquired. Caused by the deaf gene.
If one parent has the dominant gene, there is a 50% chance of deafness
If the gene is recessive, the chance is 25% Embryo is affected by disease
certain medications perinatal period - develops a few days from birth
instrument damage during birth
anoxia (lack of oxygen)
prematurity 3 kinds of hearing loss Sensorineural Hearing Loss It is also known and NERVE DEAFNESS because the inner ear or the actual auditory nerve itself is damaged. Most common; about 90% of all people who have a hearing loss suffer from sensorineural loss. Usually permanent; it is not medically or surgically treated In most cases, the cillia or the nerves from the inner ear to the brain are irreparably damaged. Causes of Sensorineural Hearing Los the natural aging process exposure to loud noises infection or other disease a genetic disorder Tinnitus, or ringing in the ears, is usually associated with sensorineural hearing loss Treatment Sensorineural hearing loss is usually permanent However, most people with this hearing loss find wearing hearing aids to be of significant benefit. Conductive Hearing Loss outer and/or middle part of the ear fail to work properly Sounds become "blocked" and are not carried all the way to the inner ear (where hearing is still normal) Not permanent; temporary hearing loss Causes a buildup of fluid in the middle ear a buildup of wax in the ear canal puncturing of the eardrum problems or injury to the bones or membrane — which carry sound from the external ear through the middle ear to the inner ear. Treatment Conductive hearing loss can be easier to remedy than sensorineural or mixed hearing loss. It is usually treatable with either medical or surgical intervention. In cases where medical/surgical intervention is not an option, a hearing aid can be very helpful. Mixed Hearing Loss A combination of a conductive and sensorineural hearing loss Both the middle and inner ear are involved Causes This hearing disorder can also occur when a person first just has a permanent sensorineural hearing loss and then also develops a conductive hearing loss. For example, a person who already has a sensorineural loss gets a middle ear infection, and the two types of loss combine to create a greater hearing loss. Some other instances of mixed hearing loss are the result of the outer and inner ear being malformed, which causes both types of hearing loss. Treatment With mixed hearing loss, the conductive part may be treated, but the sensorineural part is usually permanent. Levels of Hearing Loss Bilateral- both ears are impaired
Unilateral- one ear is impaired Bilateral loss has 4 sublevels. Mild A mild hearing loss may cause you to miss 25-40% of the speech signal. Usually this results in problems with clarity since the brain is receiving some sounds but not all of the information. Symptoms of mild hearing loss include problems understanding someone farther away than a normal distance for conversation, or even up close if the background environment is noisy. Weak voices are also difficult to understand for people with mild hearing losses. Moderate A moderate hearing loss may cause you to miss 50-75% of the speech signal. This means you would not have problems hearing at short distances and understanding people face-to-face, but you would have problems if distance or visual cues changed. Symptoms of moderate hearing loss include problems hearing normal conversations and problems hearing consonants in words Severe Hearing Loss People with severe hearing loss have difficulty hearing in all situations. A severe hearing loss may sometimes cause you to miss up to 100% of the speech signal but speech may be heard if the speaker is talking loudly or at close range. Symptoms of severe hearing loss include inability to have conversations except under the most ideal circumstances (i.e., face-to-face, in quiet, and accompanied with speechreading). Profound Hearing Loss the most extreme hearing loss. A profound hearing loss means that you may not hear any speech at all or any environmental sounds. You are forced to rely on visual cues instead of hearing as your main method of communication. This may include sign-language and/or speechreading. How Hearing Loss is Measured Decibels (dB)- the intensity (volume or loudness) of a sound A whisper is about 20 dB loud music (some concerts) is around 80 to 120 dB a jet engine is about 140 to 180 dB Usually, sounds greater than 85 dB can cause hearing loss in a few hours; louder sounds can cause immediate pain, and hearing loss can develop in a very short time The tone of sound is measured in cycles per second (cps) or Hertz. Low bass tones range around 50 to 60 Hz Shrill, high - pitched tones range around 10,000 Hz or higher The normal range of human hearing is about 16 Hz to 16,000 Hz Animals can hear up to about 50,000 Hz. Ranges have been established to help people identify how much difficulty they should expect from their hearing loss. The typical ranges for an adult are: -10dB to 25dB = Normal range 26dB to 40 dB = Mild hearing loss 41 dB to 55 dB = Moderate hearing loss 56 dB to 70 dB = Moderately Severe hearing loss 71 dB to 90 dB = Severe hearing loss over 90 dB = Profound hearing loss Audiograms
Hearing loss is plotted on an audiogram
Right ear is represented by a red circle
Left ear is represented by a blue X 10dB to 25dB = Normal hearing
26dB to 40 dB = Mild hearing loss
41 dB to 55 dB = Moderate hearing loss
56 dB to 70 dB = Moderately Severe hearing loss
71 dB to 90 dB = Severe hearing loss
over 90 dB = Profound hearing loss