Applied Anatomy of the Ear

Question 1

List the 3 divisions of the ear.

Answer 1

1 - Outer ear.

2 - Middle ear.

3 - Inner ear.

*This lecture focuses on the outer and middle ear.

Question 2

Which bone forms the bony layer of the outer ear?

Answer 2

The tympanic part of the temporal bone.

Question 3

What is the pinna of the ear?

Answer 3

The visible part of the outer ear.

Question 4

List the functions of the outer, middle and inner ear.

Answer 4

• The outer ear collects sound from the auditory space and funnels it towards the middle ear.
• The middle ear transduces sound energy into movements of joints of the ossicle chain.
• The inner ear transduces movements of the ossicle chain into electrical impulses of hearing.

Question 5

What is the isthmus of the ear?

Answer 5

The thinnest part of the auditory canal near to the tympanic membrane.

Question 6

List the embryological structures that give rise to the outer and middle ear.

Are these structures of ectodermal, mesodermal or endodermal origin?

Answer 6

• The outer ear is derived from the first pharyngeal cleft, which is of ectodermal origin.
• The middle ear is derived from the first pharyngeal pouch, which is of endodermal origin.

Question 7

List the embryological structures from which the mucosa lining the pharynx and auditory tube is derived.

Answer 7

1 - First pharyngeal pouch.

2 - Second pharyngeal pouch.

Question 8

Which embryological structure gives rise to the inner ear?

Where is this structure located during development?

Answer 8

The otic placode, which is located behind the second pharyngeal arch.

Question 9

Describe the sensory innervation of the outer ear.

Answer 9

• The upper 1/3 of the outer ear is innervated by the auriculotemporal branch of CN V3.
• The middle 1/3 of the outer ear is innervated by the lesser occipital nerve, which is a spinal nerve of roots C2 - C3.
• The lower 1/3 of the outer ear is innervated by the greater auricular nerve, which is a spinal nerve of roots C2 - C3.
• The central area of the outer ear (and continuing this, the ear canal) is innervated by the auricular branch of the vagus nerve.

Question 10

Describe the sensory innervation to the middle ear.

Answer 10

1 - The auriculotemporal branch of CN V3.

2 - The tympanic branch of CN IX.

3 - The auricular branch of CN X.

Question 11

List the embryological structures that give rise to the muscles of the middle ear.

Answer 11

• Tensor tympani is derived from the first pharyngeal arch.

- Stapedius is derived from the second pharyngeal arch.

Question 12

Which nerve innervates muscles derived from the first pharyngeal arch?

Answer 12

The mandibular branches of CN V.

Question 13

Which nerve innervates muscles derived from the second pharyngeal arch?

Answer 13

The facial nerve.

Question 14

What is perichondrium?

What is its function.

Answer 14

• The connective tissue that covers cartilage.

- It supplies the cartilage with nutrients.

Question 15

What is cauliflower ear?

Answer 15

Necrosis of the cartilage of the ear resulting from separation of the perichondrium from the cartilage due to a haematoma.

Question 16

What proportion of the external auditory canal is cartilaginous?

What proportion of the external auditory canal is formed by the temporal bone?

Answer 16

• The outer 1/3 is formed of elastic cartilage.

- The inner 2/3 is formed of the tympanic plate of the temporal bone.

Question 17

How do the innermost regions of the external auditory canal differ in appearance from the outermost regions?

Answer 17

The number of hair cells decreases towards the innermost regions.

Question 18

What is the ear-cough reflex?

Which afferent nerve is involved?

Answer 18

• Stimulation of the external auditory canal (by touch) excites the auricular branch of the vagus nerve.
• This initiates a reflex, causing a cough.

Question 19

List the layers of the tympanic membrane?

Answer 19

1 - Outer plate.

2 - Middle plate.

3 - Inner plate.

Question 20

Give an example of an indication that the tympanic membrane is attached to the ear.

Answer 20

It is concave laterally.

Question 21

Of which structure is the outer plate of the tympanic membrane a continuation?

Answer 21

The outer plate of the tympanic membrane is a continuation of the skin of the external auditory canal.

Question 22

Of which structure is the inner plate of the tympanic membrane a continuation?

Answer 22

The inner plate of the tympanic membrane is a continuation of the skin of the lining of the pharynx.

Question 23

List the cell types that comprise the lateral, middle and medial areas of the tympanic membrane.

Answer 23

• Laterally, the tympanic membrane is composed of keratinised stratified squamous cells.
• In the middle, the tympanic membrane is composed of a fibrous layer.
• Medially, the tympanic membrane is composed of respiratory epithelium (a ciliated columnar epithelium).

Question 24

Describe the sensory innervation of the tympanic membrane.

Answer 24

• The internal surface is innervated by CN IX.

- The external surface is supplied by the auriculotemporal branch of CN V3, and sometimes by the vagus nerve.

Question 25

List the surfaces of the middle ear.

Answer 25

1 - Lateral wall, formed by the inner plate of the tympanic membrane. 2 - Medial wall, formed by the outer plate of the oval window. 3 - Roof, formed by the tegmen tympanum. 4 - Floor, formed by the jugular wall. 5 - Posterior wall, formed by the mastoid wall. 6 - Anterior wall, formed by the carotid wall.

Question 26

List the bones of the middle ear.

Answer 26

1 - Malleus. 2 - Incus. 3 - Stapes.

Question 27

What is the chorda tympani? What other structure does it innervate? Why might this be relevant clinically?

Answer 27

- A sensory branch of CN VII located in the middle ear. - It also innervates the tongue for taste sensation. - This means that damage to the ear can result in changes in taste.

Question 28

What is the name of the canal connecting the middle ear to the mastoid antrum? What is the mastoid antrum?

Answer 28

- The 'aditus to mastoid antrum'. | - The mastoid antrum contains air cells that act as a reservoir of air.

Question 29

Which epithelium lines the middle ear?

Answer 29

Ciliated pseudostratified columnar epithelium similar to respiratory epithelium.

Question 30

What is the epitympanic recess?

Answer 30

A hollow located on the superior roof of the middle ear containing the aditus to mastoid antrum.

Question 31

Through which structure does the middle ear communicate with the nasopharynx?

Answer 31

The eustachian tube.

Question 32

What proportion of the eustachian tube is cartilaginous? What proportion of the eustachian tube is formed by the temporal bone?

Answer 32

- The posterolateral 1/3 is bony. | - The anteromedial 2/3 is cartilaginous.

Question 33

Which muscles open the walls of the eustachian tube? Which section of the eustachian tube is opened by these muscles?

Answer 33

- Palate levator and tensor veli palatini open the walls of the eustachian tube. - They open the anteromedial 2/3 (cartilaginous part) of the eustachian tube.

Question 34

What are the primary and secondary functions of the eustachian tube?

Answer 34

- The primary function is to equalise the pressure in the middle ear with the atmospheric pressure. - The secondary function is the drain the mucus secretions of the middle ear.

Question 35

What might result from eustachian tube dysfunction?

Answer 35

- Failure to drain mucus secretions of the middle ear, leading to congestion. - The epithelia of the middle ear begin to remove air from the secretions, producing negative pressure in the middle ear. - This is known as glue ear.

Question 36

List 3 contributing factors to otitis media Infection of the middle ear).

Answer 36

1 - Eustachian tube dysfunction. 2 - Infection of the middle ear. 3 - Nasal inflammation.

Question 37

Why are children more prone to developing otitis media than adults?

Answer 37

Because the eustachian tube in children is more horizontal.

Question 38

Why might otitis media cause the tympanic membrane to bulge into the external auditory canal?

Answer 38

Because otitis media might cause an inflammatory reaction, producing fluids in the middle ear.

Question 39

What is the most common pathogen that causes otitis media?

Answer 39

Streptococcus pneumoniae.

Question 40

What is otitis media with effusion?

Answer 40

- Otitis media where the middle ear become secretory. | - Secretions of the middle ear accumulate with products of inflammation.

Question 41

Give an example of a complication of otitis media.

Answer 41

- Mastoiditis. | - This occurs when the infection spreads to the mastoid antrum.

Question 42

List 3 areas other than the mastoid antrum into which infections causing otitis media can spread. Through which openings can this happen?

Answer 42

1 - The middle cranial fossa via the temporal bone. 2 - Posterior cranial fossa via the mastoid antrum. 3 - The sigmoid venous sinus via mastoid air cells.

Question 43

What happens in osteosclerosis of the ear?

Answer 43

The stapes fuses to the oval window, resulting in dampened movements of the ossicles.

Question 44

What is the oval window?

Answer 44

A membrane-covered opening that leads from the middle ear to the inner ear.

Question 45

Which bone forms the middle and inner ear?

Answer 45

The petrous part of the temporal bone.

Question 46

List the parts of the temporal bone.

Answer 46

1 - Squamous. 2 - Mastoid. 3 - Petrous. 4 - Tympanic.