Middle Ear Part1

Tympanic cavity is a cavity of the middle ear, it is a narrow air filled chanber in the petrous part of the temporal bone.. It is connected anteriomedially to the nasopharynx by the pharyngotympanic tube, posterosuperiorly it is connected to the mastoid cells through the mastoid antrum.

Tympanic cavity proper: space directly internal to the tympanic membrane

Tympanic recess: space superior to the membrane.

The cavity is lined with the mucous membrane. This mucous membrane is continous with the lining of the pharyngotympanic tube, mastoid cells and mastoid antrum.

CONTENTS:

Auditory ossicles (malleus, incus and stapes)

Stapedius and tensor tympani muscles

Chorda tympani nerves, a branch of CN 7

Tympanic plexus of nerves.

WALLS OF TYMPANIC CAVITY:

It has 6 walls:

1. Tegmental wall (roof): formed by a thin plate of bones, the tegmen tympani.
2. Jugular wall (floor): formed by the bony layer. This seperates the tympanic
3. Membranous wall (lateral wall): by the peaked convexity of the tympanic membrane, superiorly formed by the lateral bony walls of the epitympanic recess.
4. Labyrinthine or medial wall: seperates tympanic cavity from the internal ear promontory of labrynthine wall. Initial part of cochlea, the oval window, the round window.
5. Mastoid wall (posterior wall): opening in the superior part, the aditus to the mastoid antrum. Connects tympanic cavity to the mastoid cells. Facial nerve between the posterior wall and antrum medial to aditus.
6. Anterior carotid wall: separates tympanic cavity from carotid canal, has opening of the pharyngotympanic tube and the canal for the tensor tympani.

Mastoid Antrum:

• ·       Cavity in the mastoid process of the temporal bone.
• ·       Antrum separated from the middle cranial fossa by tegmen tympani.
• ·       Common cavity for mastoid cell opening in its floor.
• ·       Antrum and mastoid cells are covered by the mucous membrane.
• ·       Anterioinferiorly related to the canal for the facial nerve.
• ·       In mastoid antrum the facial artery passes.

Phayrngotympanic Tube:

• ·       Connects tympanic cavity to the nasopharynx.
• ·       Posterolateral third of the tube is bony. Remainder cartilaginous.
• ·       Lined by the mucous membrane.
• ·       Equalizes pressure in the middle ear with that of atmosphere, thus free movement of the tympanic membrane.
• ·       Tube opening by the expanding girth of the belly of the levator veli palatini, contracts longitudinally and tensor veli palatine pulls on the other.
• ·       Popping of the eardrums, associated with yawning and swallowing.