Middle ear (dave's notes)

Question 1

Describe the ear

Answer 1

And air space containing three auditory ossicles to transmit vibrations with a blind diverticulum from the respiratory mucosa.

Question 2

What are the major regions that constitute the middle ear?

Answer 2

Auditory tube, tympanic cavity, mastoid antrum, air cells

Question 3

What is the size of the tympanic cavity? Describe the lateral wall

Answer 3

~15mm in diameter with the tympanic membrane forming the lateral wall

Question 4

Describe the histological structure of the tympanic membrane

Answer 4

Covered externally in stratified squamous epithelium and low columnar epithelium.

Question 5

In which direction does the tympanic membrane angle?

Answer 5

Concave in, facing downwards and forwards

Question 6

What is the umbo?

Answer 6

A small depression produced by the handle of the malleolus

Question 7

What happens to the tympanic membrane from the attachment of the malleolus?

Answer 7

Two fibrous folds diverge upwards with the pars flaccid in between

Question 8

Where is the tympanic membrane held?

Answer 8

Thickened circumferentially and slotted into the groove in the tympanic plate.

Question 9

What holds the tympanic membrane tense?

Answer 9

The inward pull of tensor tympani

Question 10

What is the blood supply to the middle ear?

Answer 10

Deep auricular artery (maxillary)

Stylomastoid artery

Question 11

What is the nerve supply to the middle ear?

Answer 11

The auriculotemporal, facial and vagus nerves (meatal), and tympanic branch of the glossopharyngeal nerve (mucosal side)

Question 12

What are the five relations of the medial wall of the middle ear?

Answer 12

• Pronmontory (indented from cochlear and the tympanic plexus)
• Facial nerve canal runs above this, and the lateral semi-circular canal runs above this
• Above and behind is the oval window
• Below and behind is the round window

Question 13

What is the roof of the middle ear?

Answer 13

A laminar projection of the petrous bone and then the temporal bone in the middle cranial fossa

Question 14

What is the floor of the middle ear?

Answer 14

A thin plate of bone above the jugular fossa

Question 15

What is just anterior to the floor of the middle ear?

Answer 15

The tympanic canaliculus - entry of the tympanic branch of the glossopharyngeal nerve

Question 16

The anterior wall of the middle ear shortened and is perforated by:

Answer 16

• Lower and larger - the boney part of the auditory tube

- Upper and smaller is the canal for the tensor tympani muscle

Question 17

Where is the posterior wall of middle ear deficient?

Answer 17

Above where the aditus leads back to the tympanic antrum

Question 18

The auditory ossicles in the middle ear form a bony chain. From what arches do they develop?

Answer 18

Malleus and incus from the 1st arch cartilage

Stapes from the 2nd arch

Question 19

List the bones of the middle ear

Answer 19

Malleus
Incus
Stapes

Question 20

Is the facial nerve within the middle ear?

Answer 20

No, it passes through the petrous bone form the internal acoustic meatus to the stylomastoid foramen, passes laterally, backwards, then downwards.

Question 21

What does the facial nerve give branches to and when?

Answer 21

The facial nerve runs laterally then passes backwards above the promontory and gives branches to the tympanic plexus

Then - passes downwards medial to the aditus emerging from the stylomastoid foramen, and gives the nerve to stapedius and chordatympani at this part