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The Middle Ear
Synonym
Tympanic Cavity
Definition
The portion within the petrous portion of the temporal bone.
Structure
Lined by simple or cuboidal epithelium
Filled with air
Air reaches through the pharyngotympanic tube ( auditory or Eustachian ) tube which extends from the nasopharynx. 4 cm long – ciliated epithelium
Air pressure in the external ear and the middle ear are made equal by the eustachian tube.
This equalization helps vibration of the tympanic membrane by sound waves.
Boundaries
Laterally – tympanic membrane
Roof and floor – temporal bone
Posteriorly –temporal bone - openings - mastoid antrum - mastoid air cells.
Medial wall – temporal bone- two openings : oval window (fenestra vestibuli) - round window (fenestra cochleae)
The oval window is occluded by stapes and the round window by a fine sheet of fibrous tissue.
Auditory ossicles
Three very small bones
Extend from the tympanic membrane to the oval window
Movabel joints
They are the
1. malleus
2. incus
3. stapes
Malleus – hammer shaped – handle is in contact with the tympanic membrane and the head joints with incus
Incus – anvil shaped – body joints with the malleus and the long process joints with stapes
Stapes – stirrup shaped – head joints with incus, footplate fits into the oval window.
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