Session 7 - The Ear

Question 1

What are the four components of the temporal bone?

Answer 1

Squamous part
Petromastoid part
Tympanic plate
Styloid process

Question 2

The petrous parts of the temporal bone contain what parts of the ear?

Answer 2

Middle and inner ear

Question 3

The internal acoustic meatus transmits what two cranial nerves?

Answer 3

Facial nerve (CN VII)
Vestibulocochlear nerve (CN VIII)

Question 4

What is the mastoid antrum?

Answer 4

A prolongation of the middle ear cavity that extends into the mastoid process and communicates with air cells.

Question 5

What does the external ear consist of?

Answer 5

Pinna (or auricle)

External acoustic meatus (ear canal)

Question 6

Describe the structure of the external acoustic meatus.

Answer 6

A cartilaginous tube laterally and bony canal medially lying in the temporal bone. Lined by skin.

Question 7

What do the skin cells lining the external acoustic meatus secrete?

Answer 7

Cerumen (modified sebum).

Discarded skin cells together with cerumen form the wax.

Question 8

Are the internal and external acoustic meatus one continuous bony channel?

Answer 8

No, they are separate.

Question 9

What is another name for the ear drum?

Answer 9

Tympanic membrane

Question 10

What is another name for the middle ear?

Answer 10

Tympanic cavity

Question 11

Where are the ossicles found?

Answer 11

Middle ear

Question 12

What is the role of the ossicles?

Answer 12

Transmit vibrations from the tympanic membrane to the inner ear

Question 13

Name the ossicles.

Answer 13

Malleus
Incus
Stapes

Question 14

The apex of the eardrum is attached to what bone?

Answer 14

Malleus

Question 15

The tympanic cavity is usually air filled and enclosed from the external environment. How can communication between the tympanic cavity and external environment become possible?

Answer 15

Via the pharyngotympanic (Eustachian) tube when it opens.

Question 16

What is the pharyngotympanic (Eustachian) tube and what is its role?

Answer 16

Tube connecting the nasopharynx to tympanic cavity (middle ear). Important in allowing equalisation of air pressure between the middle ear and the atmosphere. This equalisation is needed to enable efficient transfer of sound energy to the inner ear.

Question 17

The Eustachian tube provides a potential route for what?

Answer 17

Spread of infection from the nasopharynx to the middle ear.

Question 18

How does the Eustachian tube open?

Answer 18

Intermittently opened by the pull of attached palate muscles when swallowing or yawning. (Ears ‘popping’)

Question 19

What are mastoid air cells?

Answer 19

Small air filled cavities within the bone.

Question 20

The middle ear communicates with mastoid air cells via what?

Answer 20

Mastoid aditus and antrum

Question 21

How can infection in the middle ear cavity spread to cause mastoiditis?

Answer 21

Mastoid antrum provides a connection between middle ear cavity and mastoid air cells. This provides a potential route for middle ear infections to spread leading to mastoiditis.

Question 22

What is the function of the ossicles?

Answer 22

To amplify and concentrate sound energy from the eardrum to the oval window.

Question 23

The stapes articulates with bony labyrinth of the inner ear at what point?

Answer 23

The oval window

Question 24

What branch of the fascia nerve runs through the middle ear cavity?

Answer 24

Chorda tympani

Question 25

Why can middle ear pathology potentially cause clinical signs of a facial nerve lesion?

Answer 25

Due to the proximity of the facial nerve to the middle ear (most of the facial nerve runs through the facial canal, which separates it from the middle ear by a very thin bony partition. The chord tympani branch actually runs through the middle ear cavity).

Question 26

What does the inner ear consist of?

Answer 26

Bony labyrinth - series of canals hollowed out of the petrous temporal bone surrounding the membranous labyrinth Membranous labyrinth - series of tubes/ducts

Question 27

What are the names of the ducts forming the membranous labyrinth?

Answer 27

Utricle Saccule Semicircular ducts Cochlear duct

Question 28

The ducts of the membranous labyrinth are filled with what?

Answer 28

Endolymph

Question 29

What are the names of the canals forming the bony labyrinth?

Answer 29

Semicircular canal (surround semicircular duct) Vestibule (surrounding the utricle and saccule) Cochlear (surrounding cochlear duct)

Question 30

What is the name of the fluid found between the membranous and bony labyrinths?

Answer 30

Perilymph

Question 31

Which duct houses the spiral organ of Corti?

Answer 31

Cochlear duct

Question 32

What is the function of the organ of Corti?

Answer 32

Holds the stereocilia (auditory apparatus). These respond to fluid motion within the cochlear duct (generated by the stapes ‘tapping’ on the oval window) and generate an action potential that is propagated down the cochlear part of the vestibulocochlear nerve to be perceived as sound.

Question 33

Where in the ear are stereocilia found and what are their functions?

Answer 33

Cochlear (organ of Corti) - sound perception | Utricle and saccule - rotational acceleration and the static pull of gravity