Week 7 - The Ear

Question 1

State the four components of the temporal bone.

Answer 1

1. Squamous part
2. Petromastoid part
3. Tympanic plate
4. Styloid process

Question 2

What does the external acoustic meatus mainly consist of?

Answer 2

The tympanic plate

Question 3

Which parts of the ear does the petromastoid part of the temporal bone contain?

Answer 3

The middle and inner ear

Question 4

What does the upper surface of the petromastoid part consist of?

Answer 4

Upper surface forms part of the floor of the middle and posterior cranial fossae

Question 5

Which important hole does the part forming the front of the posterior cranial fossa contain?

Answer 5

The internal acoustic meatus

Question 6

Which two cranial nerves does the internal acoustic meatus transmit?

Answer 6

1. The facial nerve

2. The vestibulocochlear nerve

Question 7

What important hole does the inferior surface of the petromastoid part of the temporal bone contain?

Answer 7

The inferior surface is irregular and contains the carotid canal

Question 8

Which important artery does the carotid canal transmit?

Answer 8

The internal carotid artery

Question 9

Through which route can middle ear disease result in mastoiditis?

Answer 9

The cavity of the mastoid antrum (prolongation of the cavity of the middle ear) extends into the mastoid process by intercommunicating air cells - middle ear disease can spread by this route to cause mastoiditis

Question 10

What secretes cerumen?

Answer 10

The skin lining the external acoustic meatus

Question 11

What is cerumen? What is its function?

Answer 11

Modified sebum - affords protection for the delicate meatal skin of the external acoustic meatus

Question 12

What forms wax?

Answer 12

The discarded cells of the skin together with cerumen

Question 13

What is the apex of the eardrum (or fibrous tympanic membrane) attached to?

Answer 13

The malleus

Question 14

What is the function of the ossicles?

Answer 14

Transmit vibrations from the tympanic membrane to the inner ear in the petrous temporal bone
The ossicles amplify and concentrate sound energy from the eardrum to the oval window

Question 15

What is the anatomical relation of the middle ear anteriorly?

Answer 15

The middle ear is communicates with the nasopharynx anteriorly via the pharyngotympanic (Eustachian tube)

Question 16

Posteriorly, what does the middle ear communicate with?

Answer 16

Posteriorly, the middle ear communicates with the mastoid air cells

Question 17

What is the function of the connection between the Eustachian tube and the middle ear?

Answer 17

Allows for equalisation of air pressure between the middle ear and the atmosphere - this is necessary for efficient transfer of sound energy to the internal ear

Question 18

When is the Eustachian tube opened?

Answer 18

Intermittently opened by the pull of attached palate muscles when swallowing (usually closed)

Question 19

Which part of the malleus attaches to the tympanic membrane and the incus?

Answer 19

The handle of the malleus is attached to the tympanic membrane
The body of the malleus articulates with that of the incus

Question 20

What type of joints exist between the ossicles?

Answer 20

Synovial joints which serve to relay the vibrations encountered by the tympanic membrane to the internal ear

Question 21

Where does the stapes articulate with the internal ear?

Answer 21

The stapes articulates with the bony labyrinth of the internal ear at the oval window

Question 22

What fluid does the membranous labyrinth contain?

Answer 22

Endolymph

Question 23

What fluid separates the bony and membranous labryinths?

Answer 23

Perilymph

Question 24

What components form the labyrinth?

Answer 24

1. Vestibule
2. Semicircular ducts and canals
3. Cochlea
4. Spiral organ of Corti

Question 25

What are the components of the vestibule?

Answer 25

1. Utricle 2. Saccule 3. Three semicircular canals All components form part of the balance system

Question 26

What does the cochlear duct accomodate?

Answer 26

The spiral organ of Corti which contains the receptors of the auditory apparatus

Question 27

What kind of receptors do the utricle and saccule contain?

Answer 27

The utricle and saccule contain receptors that respond to rotational acceleration and the static pull of gravity

Question 28

What kind of receptors do the semicircular ducts contain?

Answer 28

The semicircular ducts contain receptors that respond to rotational acceleration in three different planes

Question 29

What is the function of the stapedius muscle?

Answer 29

To dampen down excessive vibration of the stapes bone in the ear

Question 30

Outline the sensory nerve supply to the auricle.

Answer 30

1. Auriculotemporal nerve (CN V3) - Namely the area anterior to the external acoustic meatus 2. Greater auricular nerve (C2/C3) - Namely the back of the ear, the helix/antihelix and the lobule

Question 31

Outline the sensory supply to the tympanic membrane.

Answer 31

1. Auriculotemporal nerve (CN V3) - external surface | 2. Some innervation is supplied by a branch of the vagus nerve - the auricular branch

Question 32

What nerve is the internal surface of the tympanic membrane supplied by?

Answer 32

Glossopharyngeal nerve - CN IX

Question 33

Why do patients with a sore throat sometimes complain of ear pain?

Answer 33

1. Ear pain may result from infection spreading from the back of the throat or nasopharynx into the middle ear via the pharyngotympanic tube causing an otitis media 2. Ear pain can also be felt due to the shared sensory innervation of the oropharynx with the inner surface of the tympanic membrane and middle ear cavity (CN IX) 3. Hence, pain in the oropharynx secondary to infection may also result in pain being felt in the ear

Question 34

Why might a child with recurrent ear infections benefit from an adenoidectomy?

Answer 34

1. The pharyngeal tonsils or adenoids are located in the nasopharynx in close proximity to the opening of the Eustachian tube 2. They are present in young children, but subsequently shrink and disappear by early adulthood 3. In children, if the adenoids are particularly large, they may result in obstruction of the nasal passage and signs such as snoring or mouth breathing 4. Enlarged adenoids may also compress the opening of the Eustachian tube and impede its ability to drain and ventilate the middle ear 5. Dysfunction of the Eustachian tube secondary to this obstruction may lead to recurrent ear infections and/or development of otitis media with effusion 6. Removal of the adenoids allows Eustachian tube function to return