Middle Ear III

Question 1

What are the two main areas of the tympanic cavity?

Answer 1

The tympanic area proper and the attic (epitympanic recess).

Question 2

What forms the lateral (membranous) wall?

Answer 2

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.

Question 3

What forms the medial (labyrinthian) wall?

Answer 3

Oval window, round window, prominence of lateral semicircular canal, promontory, prominence of facial nerve, and portion of canal for tensor tympani.

Question 4

What is the oval window?

Answer 4

Kidney shaped opening into the vestibule of inner ear that is occupied by footplate of stapes.

Question 5

What is the round window?

Answer 5

A circular opening into the basal turn of the scala tympani of the cochlea.

Question 6

What is the promontory?

Answer 6

Rounded prominence projecting into the ME cavity. Formed by lateral projection of the basal turn of the cochlea.

Question 7

What is located in the anterior (carotid) wall?

Answer 7

Entrance to eustachian tube, and exit for tendon of tensor tympani muscle.

Question 8

What separates the carotid canal from the anterior/carotid wall?

Answer 8

Very thin plate of bone.

Question 9

What is the function of the eustachian tube? How long is it?

Answer 9

Brings aeration to the middle ear space and maintains equilibrium of pressure between the middle ear and atmosphere. 36mm in length.

Question 10

What are the portions of the eustachian tube? How long are these portions?

Answer 10

Ossesous, cartilaginous, and membranous portions. Bony portion 12 mm, cartilaginous portion is twice that.

Question 11

Where is the isthmus of the eustachian tube?

Answer 11

Junction of osseous and cartilaginous portions.

Question 12

What opens eustachian tube?

Answer 12

Tensor veli palatini, levator palatini.

Question 13

Where is the exit for the tendon of tensor tympani muscle?

Answer 13

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.

Question 14

Where is the eustachian tube located?

Answer 14

Runs from anterior wall of middle ear cavity and courses to posterior wall of nasopharynx in an inferior, medial anterior direction.

Question 15

How much of the eustachian tube is bony? Cartilaginous?

Answer 15

1/3 bony, and 2/3 cartilaginous.

Question 16

Is the lumen (bony portion) of the eustachian tube usually open or closed?

Answer 16

Usually open in bony portion, closed in cartilaginous. Cartilaginous portion opens upon action of the levator veli.

Question 17

What does the posterior mastoid wall contain?

Answer 17

Tympanic additus, pyramidal eminence, fossa, chorda tympani.

Question 18

What is the tympanic aditus?

Answer 18

Entrance to tympanic antrum which communicates with mastoid air cells.

Question 19

What is the pyramidal eminence?

Answer 19

Hollow eminence that contains stapedius muscle.

Question 20

What is the fossa?

Answer 20

Includes small evacuation in the lower and back part of the epitympanic recess that accommodates the short process of the incus.

Question 21

What is the chorda tympani? What is its function?

Answer 21

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.

Question 22

What does the roof contain?

Answer 22

Tegmen tympani- thin plate of bone that separates from cranium and meninges. Forms roof of tympanic atrum as well.

Question 23

What does the floor contain?

Answer 23

Tympanic plate forms floor. Separates cavity from jugular fossa, which houses jugular vein. Narrower than roof.

Question 24

What is the middle ear cavity?

Answer 24

Air filled space situated between outer ear and inner ear within petrous portion of temporal bone.