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What is the Eustachian tube?

The Eustachian tube

is a membrane lined

tube (approximately35 mm long) that

connects the middle

ear space to the back

of the nose (thePharynx).

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What are the functions of the Eustachian tube?

Pressure equalization: The Eustachian tube starts out closed, but can be

opened to allow a small amount of air to enter themiddle ear to allow pressure equalization with the

atmosphere. When this happens, we hear a small “pop.” Yawning and

swallowing can cause muscles to tighten in the neck, causingthe tube to open. 

Mucus drainage:

The tube drains mucus, keeping ears from becoming“stuffy.” Mucus stuck in the tympanic cavity candevelop a high level of pressure, and can lead to ear infections if bacteria becomes present.

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The Relation Between Ear Infections and the Eustachian Tube:

Most commonly by allergies and sickness, the Eustachiantube is prone to swelling and allowing germs into the middleear, these germs can eventually lead to an infection.

In children, the Eustachian tube runs horizontally rather than sloping downward, causing foreign objects to enter themiddle ear more easily. This is why chronic ear infectionsare more prominent in younger children.

Ear infections are the second most common diagnosed

illness in children behind only the common cold. More than75% children have had an ear infection by the time theyhave reached the age of three.

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The Inner Ear  The inner ear consists of:

The Cochlea (Latin for snail .)

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The CochleaThe cochlea is a snail-like structure divided

into three fluid-filled

compartments.

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The Process

Inside the cochlea, the vibrational signal

from the middle air passes through fluid

until reaching the Organ of Corti, where itis turned into electrical impulses when

coming in contact with “hair cells” and

finally exits through the auditory nerve intothe brain.

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Organ of Corti

The Organ of Corti has highly specialized

structures that respond to fluid-borne vibrations

in the cochlea by movement of hair cells. The Organ of Corti has “hair cells,” which are located

atop a thin basilar membrane.

Once destroyed, these hair cells are not replaced.

The hair cells responsible for higher frequencies areparticularly sensitive and fragile (frequencies used

when interpreting human speech!)

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“Hair Cells” or auditory sensory cells. 

Outer Hair Cells Outer hair cells act as

preamplifiers for higher frequencies, enhancing frequencyselectivity.

Inner Hair Cells Due to the type of fluid

[endolymph, a positive-ion richfluid] surrounding the Organ of Corti, vibrations from the soundopen a flow of ions to the cellwhich results in an electric signalbeing sent to the auditory cortexwhen deflected (moved).

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Practical Application

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 The Dynamics of Hearing Pt. 1

The audible sound range is generally definedas 20 Hz to 20,000 Hz (20 kHz), thoughsome can reportedly hear up to 22 kHz.

Scientists define this range as “audio.”  Middle aged people tend to lose the ability to

hear well from 10-20 kHz, partly due tonatural aging, but also due to hearing

damage.