MIDDLE EAR -

1. Protected by tympanic bone. It's cavity is tympanic cavity.
2. It is lined by simple cilliated columnar epithelium. It is connected to naso pharynx by Eustachian canal.
3. Here valve is present, generally closed, during shouting, yawning & swallowing it is opened.
4. Due to it on both sides of tympanum, pressure of air is equalized. Inflamation of eustachian tube is eutachitis.
5. Cold may block the eustachian tube & the pressure outside and inside the middle ear do not equalige. So divers and fliers do not work when they have cold. Outside preesure is increases in diving & decresed in flying.
6. Middle ear is connected to internal ear by fenestra ovalis or oval window and fenestra rotundus or round window.
7. By fenestra ovalis sound waves enter in to internal ear. By fenestra rotundus sound waves come out if strong.
8. Between tympanum and fenestra ovalis there is a chain of 3 bones collectively called as ear ossicles.
9. Three bones are malleus, inchus & stapes. Malleus is hammer shaped attached to tympanum.
10. Inchus is anvil shaped. Stapes is stirrup shaped, smallest bone with bone marrow.
11. All bone are articuluted by hinge joint & fixed in position due to their respective ligaments.
12. These bones are modification of articular, quadrate and hyomendibular.
13. In frog collumella auris present, which is modification of hyomendibular.
14. Ear ossicles transmit the vibration from the tympanic membrane to internal ear and also amplify them about 20 times.
15. Two small muscles tensor tympani and stapedius, joined to malleus and stapes respectively, contract to prevent damage to the dellicate internal ear at the time of loud sound.