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      Medial wall of middle ear is formed by labyrinth.

   Structures are-

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.

  • SURGICAL IMPORTANCE:

       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.

  1. It acts as the landmark for the first genu of the Facial nerve.

 

*** 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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