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Middle Ear

Audiology PowerPoint 4

Eustachian tube named after Bartolomeo Eustachi
Ossicular chain definition (and how is it affected by muscle contraction?) Made up of 3 ossicles that link the tympanic membrane to the oval window of the cochlea. Needs support (ligaments) and control (muscles via tendons). Muscle contraction causes rigidity and movement restriction.
Ossicles Malleus, Incus, Stapes
V cranial nerve innervates _____ which connects to tensor tympani muscle, (tensing of head/neck muscles), ligament to the malleus
V cranial nerve trigeminal nerve
VII cranial nerve facial nerve
VII cranial nerve innervates _____ which connects to stapedius muscle (activated by loud sound, pulls head of stapes at right angle to direction of movement of ossicular chain), ligament to the stapes
Tympanic cavity air filled space behind the TM lined with epithelium
Epitympani recess superior area of the cavity, hosts the head of the malleus and the incus
Eustachian tube canal that connects middle ear to nasopharynx, drains fluid from middle ear and equilibrates ME and external pressures.
Function of Middle Ear transmits and amplifies vibrations of the tympanic membrane to inner ear
Oval window hidden by the footplate of the stapes, separates ME from IE
Why must the ME amplify acoustic pressure? The sound is amplified in preparation for the loss of pressure by transferring the vibration from air to fluid. 98% of energy would be lost without amplification
Explain the "Thumbtack Effect" The tympanic membrane is 17x larger tthan the oval window, and so all of the pressure is the concentrated on one small spot. (Pressure=Force/Area, reduction of Area increases pressure). This adds 23 dB.
Otitis Media eustachian tube fails to drain fluid within ME cavity, causing fluid to accumulate behind TM. Bacteria or viruses from nose invade fluid -> infection. Common in children.
Myringotomy for Otitis Media, the procedure for inserting a tube in the TM to drain out fluid
Cholesteatoma expanding growth of accumulating dead skin cells in the middle ear (benign tumor), begins on TM above pars flaccida. Produces enzymes causing destruction of bone.
Otosclerosis Ossicles become knit together into an immovable mass causing conductive hearing loss. Can affect the otic capsule (surrounding IE) and cause stapes fixation.
At its resting state, the eustachian tube is... collapsed
Function of the tensor veli palatini When we swallow or yawn, tensor veli palatini contracts and causes the eustachian tube to open allowing the equalization of pressure between ME and external environment.
Explain the "Lever Effect" The incus has a short crus and a long crus, and therefore acts as a lever when transmitting vibrations from the malleus to the stapes. Amplifies the pressure by 3 dB.
Aside from the Lever Effect and the Thumbtack Effect, what else amplifies the acoustic pressure? The curve of the tympanic membrane adds 6 dB
Tympanostomy the act of cutting the tympanic membrane. --But NOT of putting in a tube.
Three reasons children under 3 get otitis media so often 1) muscle tensor veli palatini is not developed, 2) not enough cartilage to support, 3) eustachian tube is horizontal
Difference in pressure between ME and outside environment would... prevent you from hearing sound well.
If the eustachian tube is blocked... air can not move in and out of the middle ear cavity --> bad conduction of sound and differences of air pressure may bruise or rupture the TM.
How does a cholesteatoma form? Skin lines the EAM and the outer surface of the TM. The outermost layer of skin on TM is actually composed of dead cells which are constantly being expelled with cerumen.
What are the consequences of a cholesteatoma? Conductive hearing loss when deteriorates occiscles, but if it reaches the otic capsule can cause sensorioneural hearing loss. The bone over the facial nerve can also be destroyed and a facial paralysis can result.
Ossicular chain dislocation occurs with... Occur w/ temporal bone fracture, traumatic TM perforation or barotrauma
Most common form of ossicular chain dislocation: separation of the joint connecting the incus to the stapes
Treatment of ossicular chain dislocation in most common case: ossicular chain reconstruction.
Treatment for otosclerosis: prosthesis and/or stapedectomy.
Created by: 100000299709410



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