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AFFECTED ANATOMY

Diagram of the Human Ear Anatomy

Note:The complete anatomy of the ear is extensive, and can be divided into theinner earandouter ear.

The remainder of this article mainly references thecochlea, outerhair cells, andOrgan of Corti.

In general, structural damages to any anatomical part of the ear can cause hearing-related

problems. Usually, minor bending of the stereocilia (inner ear) is associated with temporary

hearing loss and is involved in auditory fatigue. Complete loss of the stereocilia causes

permanent hearing damage and is more associated with noise-induced hearing loss and other

auditory diseases.

Theouter hair cells, or OHCs, can be thought of as microamplifiers that provide stimulation to

theinner hair cells. The OHCs are the most fragile of the hair cells, hence their involvement in

auditory fatigue and other hearing impairments.

http://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/Inner_earhttp://en.wikipedia.org/wiki/Inner_earhttp://en.wikipedia.org/wiki/Outer_earhttp://en.wikipedia.org/wiki/Outer_earhttp://en.wikipedia.org/wiki/Outer_earhttp://en.wikipedia.org/wiki/Cochleahttp://en.wikipedia.org/wiki/Cochleahttp://en.wikipedia.org/wiki/Cochleahttp://en.wikipedia.org/wiki/Hair_cellshttp://en.wikipedia.org/wiki/Hair_cellshttp://en.wikipedia.org/wiki/Hair_cellshttp://en.wikipedia.org/wiki/Organ_of_Cortihttp://en.wikipedia.org/wiki/Organ_of_Cortihttp://en.wikipedia.org/wiki/Organ_of_Cortihttp://en.wikipedia.org/wiki/Stereocilia_(inner_ear)http://en.wikipedia.org/wiki/Stereocilia_(inner_ear)http://en.wikipedia.org/wiki/Hair_cells#Outer_hair_cells_.E2.80.93_acoustical_pre-amplifiershttp://en.wikipedia.org/wiki/Hair_cells#Outer_hair_cells_.E2.80.93_acoustical_pre-amplifiershttp://en.wikipedia.org/wiki/Hair_cells#Outer_hair_cells_.E2.80.93_acoustical_pre-amplifiershttp://en.wikipedia.org/wiki/Hair_cells#Inner_hair_cells_.E2.80.93_from_sound_to_nerve_signalhttp://en.wikipedia.org/wiki/Hair_cells#Inner_hair_cells_.E2.80.93_from_sound_to_nerve_signalhttp://en.wikipedia.org/wiki/Hair_cells#Inner_hair_cells_.E2.80.93_from_sound_to_nerve_signalhttp://en.wikipedia.org/wiki/File:Anatomy_of_the_Human_Ear.svghttp://en.wikipedia.org/wiki/Hair_cells#Inner_hair_cells_.E2.80.93_from_sound_to_nerve_signalhttp://en.wikipedia.org/wiki/Hair_cells#Outer_hair_cells_.E2.80.93_acoustical_pre-amplifiershttp://en.wikipedia.org/wiki/Stereocilia_(inner_ear)http://en.wikipedia.org/wiki/Organ_of_Cortihttp://en.wikipedia.org/wiki/Hair_cellshttp://en.wikipedia.org/wiki/Cochleahttp://en.wikipedia.org/wiki/Outer_earhttp://en.wikipedia.org/wiki/Inner_earhttp://en.wikipedia.org/wiki/Earhttp://en.wikipedia.org/wiki/File:Anatomy_of_the_Human_Ear.svg

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Temporary Threshold Shift

Temporary threshold shift is a protection mechanism that allows our hearingto adapt to the environment. This mechanism is in play all of the time,

especially in the recording studio.

Noise exposure and intense sounds can cause two main types of hearing loss, namelytemporary threshold shift and permanent threshold shift.

Temporary threshold shift is mostly experienced as a temporary dullness in your hearing afterexposure to loud noises. Your hearing will subsequently recover - depending on how loud thenoises have been and how long you have been exposed to them.

Permanent threshold shift is first experienced 48 hours after exposure to excessive noise.Permanent threshold shift can occur if you have been regularly exposed to excessive noise forlong periods of time. It can also occur if you are exposed to very high sound levels for a shortperiod of time. This type of hearing loss will normally continue to increase for up to five years

after exposure to the noise.

Exposure to noise and high sound levels can also result in Tinnitus - a constant sound in yourears or head.

Temporary Loss of Hearing

If your ears are ringing or sounds seem muted and distant after you've been in a noisy

environment, you are experiencing a type of hearing loss, which is probably temporary. This

happens because the delicate hair cells in your inner ear have been overworked and are

fatigued,and are not functioning as well as usual.

A temporary loss of hearing is sometimes called "temporary threshold shift." This

refers to your hearing threshold, which is the softest sound that you are able to

hear. If the decibel level of the softest sound audible to you is higher than usual,

your threshold of hearing has shifted upward.

Restoring Your Normal Hearing

If a hearing loss is temporary, your hearing can recover if you give it the chance.That means leaving the noisy environment, or usinghearing protectionif leaving isnot immediately possible. Then you'll want to rest your ears, avoiding high levels ofnoise for 24 hours, ideally keeping your noise exposure below 70 decibels.

Your ears should normally recover within 16 hours. If your hearing has not returned

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to normal after 48 hours, the hair cells have been unable to recover. Since hair cellsdo not grow back, you've experienced permanenthearing damage.

Auditory fatigue is defined as a temporary loss of hearing after exposure to sound. This results

in a temporary shift of the auditory threshold known as a temporary threshold shift(TTS). The

damage can become permanent (permanent threshold shift, PTS) if sufficient recovery time isnot allowed for before continued sound exposure. When the hearing loss is rooted from a

traumatic occurrence, it may be classified asnoise-induced hearing loss, or NIHL.

There are two main types of auditory fatigue, short-term and long-term.These are distinguished

from each other by several characteristics listed individually below.

Short-term fatigue

full recovery from TTS can be achieved in approximately two minutes

the TTS is relatively independent of exposure duration

TTS is maximal at the exposure frequency of the sound

Long-term fatigue

recovery requires a minimum of several minutes but can take up to days

dependent on exposure duration and noise level

On exposure to NOISE, the ear's sensitivity level will decrease as a measure of

protection. This process is referred to as a shift in the THRESHOLD OF HEARING,

meaning that only sounds louder than a certain level will be heard. The shift may be

temporary, chronic or permanent.

Susceptibility to TS varies greatly from person to person, men generally being more

sensitive to low frequency sounds, and women more susceptible to high frequencies.

Sounds in the 2 - 6 kHz range seem to induce greater temporary threshold shift (TTS)

than other frequencies. Also called aural fatigue.

Thus, TTS implies a temporaryHEARING LOSSfor low level sounds

One of the body's reactions to loud sounds is a constriction of the blood vessels

(vasoconstriction) which reduces the blood supply reaching the hair cells of theORGAN OF CORTI. The outer rows of hair cells respond mainly to low intensity sound

levels and thus are easily saturated by loud sounds, particularly when their source of

blood is diminished. This leaves only the inner rows of hair cells working since they

need a higher intensity for stimulation.

http://www.noisehelp.com/impaired-hearing.htmlhttp://www.noisehelp.com/impaired-hearing.htmlhttp://www.noisehelp.com/impaired-hearing.htmlhttp://en.wikipedia.org/wiki/Noise-induced_hearing_losshttp://en.wikipedia.org/wiki/Noise-induced_hearing_losshttp://en.wikipedia.org/wiki/Noise-induced_hearing_losshttp://www.sfu.ca/sonic-studio/handbook/Noise.htmlhttp://www.sfu.ca/sonic-studio/handbook/Noise.htmlhttp://www.sfu.ca/sonic-studio/handbook/Threshold_of_Hearing.htmlhttp://www.sfu.ca/sonic-studio/handbook/Threshold_of_Hearing.htmlhttp://www.sfu.ca/sonic-studio/handbook/Hearing_Loss.htmlhttp://www.sfu.ca/sonic-studio/handbook/Hearing_Loss.htmlhttp://www.sfu.ca/sonic-studio/handbook/Hearing_Loss.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Hearing_Loss.htmlhttp://www.sfu.ca/sonic-studio/handbook/Threshold_of_Hearing.htmlhttp://www.sfu.ca/sonic-studio/handbook/Noise.htmlhttp://en.wikipedia.org/wiki/Noise-induced_hearing_losshttp://www.noisehelp.com/impaired-hearing.html

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If the outer hair cells are not allowed to recover through periods of quiet, they

gradually lose their ability to respond and eventually die. TTS may also be

accompanied byTINNITUS, a ringing in the ears.

Temporary Threshold Shift (TTS): During short exposure to noise, most people

experience a rise in the auditory threshold which normally disappears in 24 hours, but

may last as long as a week.

Permanent Threshold Shift (PTS) or Noise Induced Permanent Threshold Shift

(NIPTS): After prolonged exposure to noise, permanent hearing damage may result in

theINNER EAR(seeACOUSTIC TRAUMA,ORGAN OF CORTI,PRESBYCUSIS).

Chronic Threshold Shift or Compound Threshold Shift: If exposure to noise occurs

repeatedly without sufficient time between exposures to allow recovery of normal

hearing, TS may become chronic, and eventually permanent. This is a particular

danger when people who work in noisy environments are exposed to further noise

afterwards in driving, at home and at places of entertainment (seeSOCIOCUSIS).

Permanent Threshold Shift

PTS may occur as a result of long-term exposures and/or extremely loud noises.

Repeated exposures that cause to temporary threshold shift (TTS) can induce PTS,

as well. It is an unrecoverable deafening due to physiological damage to thehearing organs that does not diminish with time.

Permanent threshold shift is first experienced 48 hours after exposure to excessive noise.

Permanent threshold shift can occur if you have been regularly exposed to excessive noise for

long periods of time. It can also occur if you are exposed to very high sound levels for a short

period of time. This type of hearing loss will normally continue to increase for up to five years

after exposure to the noise.

Exposure to noise and high sound levels can also result in Tinnitus - a constant sound in your

ears or head.

http://www.sfu.ca/sonic-studio/handbook/Tinnitus.htmlhttp://www.sfu.ca/sonic-studio/handbook/Tinnitus.htmlhttp://www.sfu.ca/sonic-studio/handbook/Tinnitus.htmlhttp://www.sfu.ca/sonic-studio/handbook/Inner_Ear.htmlhttp://www.sfu.ca/sonic-studio/handbook/Inner_Ear.htmlhttp://www.sfu.ca/sonic-studio/handbook/Inner_Ear.htmlhttp://www.sfu.ca/sonic-studio/handbook/Acoustic_Trauma.htmlhttp://www.sfu.ca/sonic-studio/handbook/Acoustic_Trauma.htmlhttp://www.sfu.ca/sonic-studio/handbook/Acoustic_Trauma.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Presbycusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Presbycusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Presbycusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Sociocusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Sociocusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Sociocusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Sociocusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Presbycusis.htmlhttp://www.sfu.ca/sonic-studio/handbook/Organ_of_Corti.htmlhttp://www.sfu.ca/sonic-studio/handbook/Acoustic_Trauma.htmlhttp://www.sfu.ca/sonic-studio/handbook/Inner_Ear.htmlhttp://www.sfu.ca/sonic-studio/handbook/Tinnitus.html

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Acceptable Noise - dBA - Levels

Acceptable noise - dBA - levels at some locations

LOCATION EFFECTS MAXIMUM (dBA) TIME (HOURS) TIME OF DAY

Bedroomsleep disturbance,

annoyance30 8 night

Living areaannoyance, speech

interference50 16 day

Outdoor living area moderate annoyance 50 16 day

Outdoor living area serious annoyance 55 16 day

Outdoor living areasleep disturbance, with

open windows45 8 night

School classroomspeech interference,

communicationdisturbance

35 8 day

Hospitals patientrooms

sleep disturbance,communication

interference30 - 35 8 day and night

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