Medial wall of middle ear is formed by labyrinth.
1) Promontory: A bulge, due to basal coil of cochlea.
2) Oval Window: Fixed the foot plate of stapes.
3) Round window: Covered by secondary TM.
4) Canal for Facial Nerve: Above the oval window.
5) Prominence of lateral semi circular canal: Above the canal for facial nerve.
6) Processus cochleaformis: A hook like projection anterior to oval window. The tendon of tensor tympani takes a turn here to get attachment to neck of malleus.
7) Sinus tympani: Medial to pyramid is a deep recess bounded by subclavian below & ponticulous above.
PROCESSUS COCHLEAFORMIS: Marks the level of Genu of facial nerve which is important landmark for surgery of Facial nerve.
** This is the common wall between middle ear & inner ear.
** Two significance- 1. Tensor tympani muscle originates from a canal in the anterior wall of middle ear.
*** Important impedance matching mechanism of middle ear
Middle ear takes an important role in conduction of sound.
A person under water cannot hear any sound made in air as sound energy 99.9% is reflected away from the surface of water because of impedance offered by it.
A similar situation exists in ear when air conducted sound has to travel to cochlear fluids.
Nature has compensated for this loss of sound energy by interposing the middle ear.
Middle ear converts sound.
Greater amplitude but lesser force→ (to impedance matching mechanism)→→→ Lesser amplitude but greater force → It is accomplished by- 1) Lever action of ossicles 2) Hydraulic action of TM.
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