Middle Ear III Flashcards
What are the two main areas of the tympanic cavity?
The tympanic area proper and the attic (epitympanic recess).
What forms the lateral (membranous) wall?
Most is formed by the eardrum. Above this, in the epitympanic recess, the lateral wall is formed by part of the squamous portion of temporal bone.
What forms the medial (labyrinthian) wall?
Oval window, round window, prominence of lateral semicircular canal, promontory, prominence of facial nerve, and portion of canal for tensor tympani.
What is the oval window?
Kidney shaped opening into the vestibule of inner ear that is occupied by footplate of stapes.
What is the round window?
A circular opening into the basal turn of the scala tympani of the cochlea.
What is the promontory?
Rounded prominence projecting into the ME cavity. Formed by lateral projection of the basal turn of the cochlea.
What is located in the anterior (carotid) wall?
Entrance to eustachian tube, and exit for tendon of tensor tympani muscle.
What separates the carotid canal from the anterior/carotid wall?
Very thin plate of bone.
What is the function of the eustachian tube? How long is it?
Brings aeration to the middle ear space and maintains equilibrium of pressure between the middle ear and atmosphere. 36mm in length.
What are the portions of the eustachian tube? How long are these portions?
Ossesous, cartilaginous, and membranous portions. Bony portion 12 mm, cartilaginous portion is twice that.
Where is the isthmus of the eustachian tube?
Junction of osseous and cartilaginous portions.
What opens eustachian tube?
Tensor veli palatini, levator palatini.
Where is the exit for the tendon of tensor tympani muscle?
Parallel to eustachian tube, separated by thin bone plate. Arises from medial portion of wall which is marked by the trochleariform, which is a pulley for process.
Where is the eustachian tube located?
Runs from anterior wall of middle ear cavity and courses to posterior wall of nasopharynx in an inferior, medial anterior direction.
How much of the eustachian tube is bony? Cartilaginous?
1/3 bony, and 2/3 cartilaginous.
Is the lumen (bony portion) of the eustachian tube usually open or closed?
Usually open in bony portion, closed in cartilaginous. Cartilaginous portion opens upon action of the levator veli.
What does the posterior mastoid wall contain?
Tympanic additus, pyramidal eminence, fossa, chorda tympani.
What is the tympanic aditus?
Entrance to tympanic antrum which communicates with mastoid air cells.
What is the pyramidal eminence?
Hollow eminence that contains stapedius muscle.
What is the fossa?
Includes small evacuation in the lower and back part of the epitympanic recess that accommodates the short process of the incus.
What is the chorda tympani? What is its function?
Small banch of facial nerve that joins branch of trigeminal nerve. Enters from posterior wall and leaves above and in front of tympanic sulcus. Supplies sensory innervation (taste) to anterior 2/3 of tongue and motor innervation to a few glands in mouth.
What does the roof contain?
Tegmen tympani- thin plate of bone that separates from cranium and meninges. Forms roof of tympanic atrum as well.
What does the floor contain?
Tympanic plate forms floor. Separates cavity from jugular fossa, which houses jugular vein. Narrower than roof.
What is the middle ear cavity?
Air filled space situated between outer ear and inner ear within petrous portion of temporal bone.
