Anatomy

Question 1

1. Which bone of the skull is the middle ear situated in?

Answer 1

Temporal bone of the skull

Question 2

2. Name the 3 auditory ossicles middle ear?

Answer 2

Malleus, Incus, Stapes

Question 3

3. What constitutes the roof and floor of the middle ear?

Answer 3

Roof - Petrous part of the temporal bone (separate the middle ear from the middle cranial fossa)
Floor - Jugular wall (separate middle ear from internal jugular vein)

Question 4

4. What are the two muscles of the middle ear and explain their function?

Answer 4

Stapedius muscle and tensor tympani muscle - Acoustic reflex (regulate the movement of the auditory bones of the middle ear. E.g. when loud sounds are hear the muscles contract to reduce the vibration of the bones hence reducing the amplitude of the sound)

Question 5

5. Name the innervation of the two muscles of the middle ear?

Answer 5

Stapedius muscle - Facial nerve (CN VII)

Tensor tympani muscle - Mandibular branch of Trigeminal nerve (CN V3)

Question 6

6. What are the two openings in the anterior wall of the middle ear for?

Answer 6

Eustachian tube and tensor tympani muscle

Question 7

7. What is the function of the Eustachian tube?

Answer 7

Equalise the pressure inside the middle ear to normal environmental air pressure

Question 8

8. Why are children more prone for middle ear infections (otitis media) than adults?

Answer 8

In children the Eustachian tube is shorter, more horizontal and the lumen is wider. Therefore, children are more prone for infection.

Question 9

9. How many layers does the tympanic membrane consists of and name the layers?

Answer 9

Three. They are the Outer epithelial/cutaneous layer, middle fibrous layer and inner mucosal layer

Question 10

10. Name the embryological origins of the layers of the tympanic membrane?

Answer 10

Outer epithelial layer: Ectoderm
Middle fibrous layer: Mesoderm
Inner mucosal layer: Endoderm

Question 11

11. Name the area of the tympanic membrane which lacks the middle fibrous layer?

Answer 11

Pars flaccida (Rivinus membrane/Shrapnell’s membrane)

Question 12

12. To which quadrant of the tympanic membrane is a myringotomy incision made? (incision made in the tympanic membrane to remove fluid accumulated in the middle ear)

Answer 12

Postero-inferior quadrant to avoid injury to the chordae tympani nerve