Anatomy of the Ear

Question 1

What is the structure of the external ear?

Answer 1

Auricle or Pinna is your “ear,” the part outside of your temporal bone.

It has stratified keratinising squamous epithelium (skin)
Elastic cartilage

This flows to the external acoustic meatus

• lateral 1/3 cartilage and skin
• Medial 1/3 bone and skin

The deep parts of the external ear have:

• Sebaceous glands
• Ceruminous glands (produce wax)

Question 2

What is otitis externa?

Answer 2

Inflammation of the external ear

Question 3

What is the tympanic membrane?

Answer 3

1cm diameter approx

3 layers:

• Outer squamous epithelium
• Middle fibrous connective tissue
• inner columnar ciliated mucous membrane (respiratory)

Perforation by trauma, suppuration
Part of sound conduction

Question 4

What is the eustachian tube?

Answer 4

Auditory tube or eustachian tube

Connection between middle ear and nasal canal
Keeps equal pressure in inner ear
Holding your nose and breathing out or swallowing will open the tube and let air in

Question 5

What is the ossicular chain?

Answer 5

KEY role in sound production
Disruption by: 
-Trauma, 
-Chronic suppuration, 
-Bony sclerosis (otosclerosis)

Made up of the malleus, incus and stapes

Question 6

What is otosclerosis and how is it managed?

Answer 6

Thickening or proliferation of bone around the stapes
This prevents it from moving as well as its more fixed
As a result sound isn’t conducted

To fix the stapes is bypassed
-Remove stapes (stapedectomy)
-Fix small pole into stapes footplate
-Join to incus by thin fibre
Sound can now be conducted

Question 7

Give a brief overview of the middle ear

Answer 7

Lined by columnar ciliated epithelium
-mucous, cataarh, glue

Contains:

• ossicles
• facial nerve and chorda tympani

Two main spaces:

• epitympanum (attic)
• hypotympanum

Question 8

Where does the middle ear connect to?

Answer 8

Mastoid system via aditus

Post-nasal space via eustachian tube

Question 9

What important relations does the middle ear have?

Answer 9

Middle fossa
Internal jugular vein
Internal carotid artery

Question 10

Discuss the facial nerve

Answer 10

Great importance to surgeon
Cosmetic and functional importance of damage
Medial wall of middle ear - horizontal

Lies in the bony (fallopian) canal
10% dehiscent (isn’t covered by fallopian canal- more at risk)

Stylomastoid foramen to parotid

Question 11

Describe the inner ear

Answer 11

Vestibulo-cochlear organ of balance and hearing

Consists of a bony labyrinth containing:

• Cochlea
• Vestibule (in the centre)
• Semi-circular canal

Inside this bony labyrinth is a membranous labyrinth of sensory epithelium

There are two types of fluid in the inner ear:

• Perilymph
• endolymph

Question 12

Describe the nerve pathway of hearing

Answer 12

Cochlear fibres form the cochlear nerve
The cochlear nerve joins with the vestibular nerve to form the vestibulo-cochlear nerve.
This travels through the internal auditory meatus
Joins brainstem at junction of pons and medulla

Question 13

Describe the innervation of the ear

Answer 13

Mixed innervation to the ear:

• Cervical nerve root branches
• 5th nerve (Trigeminal Nerve)
• 9th Nerve (Glossopharyngeal Nerve)
• 10th Nerve (Vagus nerve)

This mixture of nerves gives common referred pain of the ear

Question 14

Describe the internal auditory meatus

Answer 14

Junction of inner ear -> brainstem
1cm long bony canal

Contains:

• 8th cranial nerve (vestibulo-cochlear)
• 7th cranial nerve (facial)

Clinical site of:

• Acoustic neuroma
• vestibular schwannoma