Anatomy of the Ear and Auditory Tube

Question 1

What anatomical landmarks distinguish the borders of the outer, middle and inner ear respectively?

Answer 1

Outer: from auricle to tympanic membrane
Middle: from tympanic membrane to round and oval windows
Inner: cavity extending into the petrous part of the temporal bone from the round and oval windows

Question 2

What is the role of the auricle?

Answer 2

Cartilaginous structure which helps to collect sound

Question 3

Describe the nervous supply of the external acoustic meatus

Answer 3

Vagus supplies the posteroinferior walls

Auriculotemporal (from CNV3) supplies anterosuperior walls and external surface of tympanic membrane

Question 4

What is the significance of the nerve supply of the tympanic membrane?

Answer 4

Pain can be referred to or from other branches of CNV3 (e.g. lower teeth)

Question 5

What lines the external acoustic meatus and why?

Answer 5

Hairy skin and cerumen glands to prevent maceration of the skin with water

Question 6

Describe the structure of the external acoustic meatus

Answer 6

Lateral 1/3 is cartilaginous

Medial 2/3 is bony (temporal bone)

Question 7

What is the role of tympanic membrane?

Answer 7

Vibrates with the frequency and amplitude of the incoming sound to transfer this sound through to the inner ear via the ossicles

Question 8

What is the significance of the “cone of light” seen through an oroscope when examining the tympanic membrane?

Answer 8

Should be located in the anteroinferior quadrant; light reflecting elsewhere may indicate a pressure build-up behind the tympanic membrane

Question 9

What is the epitympanic recess?

Answer 9

An opening above the tympanic membrane that communicates posteriorly with the mastoid air cells

Question 10

What is the role of the auditory tube?

Answer 10

Projects anteroinferiorly to the nasopharynx allowing for equalization of pressure to the middle ear and drainage of inflammatory exudate

Question 11

What is the difference between the auditory tube in childhood and adulthood and how is this clinically relevant?

Answer 11

More horizontally orientated in childhood, meaning drainage is more difficult and children are therefore more prone to infections of the middle ear
These infections can affect hearing as the mucus stifles the movement of the ossicles

Question 12

What is the name of the main cavity in the middle ear?

Answer 12

Tympanic cavity proper

Question 13

What are the 3 ossicles of the middle ear, in order of most lateral to most medial?

Answer 13

Malleus, incus, stapes

Question 14

What is the name of the process projecting from the malleus that communicates with the tympanic membrane?

Answer 14

Handle

Question 15

What is the name of the process projecting from the body of the incus to articulate with the head of the stapes?

Answer 15

Lenticular process

Question 16

What is the role of the stapedius and tensor tympani muscles?

Answer 16

To dampen the amplitude of vibration when the volume of sound is excessive

Question 17

Which nerve innervates stapedius?

Answer 17

CNVII

Question 18

Which nerve innervates tensor tympani?

Answer 18

Trigeminal

Question 19

Where does stapedius attach?

Answer 19

To stapes

Question 20

Where does tensor tympani attach?

Answer 20

To malleus

Question 21

Which ossicle overlies the oval window?

Answer 21

Stapes

Question 22

Describe the course of the internal carotid artery

Answer 22

Runs straight underneath the middle ear through the carotid canal, and makes an S-shaped bend at foramen lacerum

Question 23

Describe the structure of the inner ear

Answer 23

A bony labyrinth filled with perilymph, containing a membranous labyrinth filled with endolymph

Question 24

List the 4 different components of the membranous labyrinth

Answer 24

Vestibule containing utricle and saccule
Cochlea with cochlear duct
Anterior, horizontal and posterior semicircular canals
Ampullas