Anatomy and Physiology of the Ear

Question 1

What sections is the ear separated into?

Answer 1

• External
• Middle
• Inner

Question 2

What type of epithelium is found in the external auditory canal?

Answer 2

Stratified keratinised epithelium (skin) - with elastic cartilage

Question 3

What are the features of the lateral 1/3 of the auditory canal?

Answer 3

• Made of skin and cartilage
• Skin contains ceruminous and sebaceous glands (produce wax)
• Protective barrier and disinfectant

Question 4

What are the features of the medial 2/3 of the auditory canal?

Answer 4

• Made of skin and bone
• No hairs or cilia
• Doesn’t produce wax

Question 5

Describe the cycle of skin renewal

Answer 5

Skin of external ear canal is constantly bine shed and renewed. It grows from the umbo of the tympanic membrane outwards.

The skin is shed in the lateral 1/3rd of the canal and becomes trapped in the wax as part of the cleaning mechanisms

Question 6

What are four conditions that can affect the external ear?

Answer 6

• Pinna haematoma
• Otitis externa
• Fungal OE
• Foreign body

Question 7

What is pinna haematoma?

Answer 7

Trauma common during sports where shearing forces can lead to separation of the anterior auricular perichondrium from the underlying cartilage. As a result, blood vessels and be torn.

If not drained early, the haematoma can lead to necrosis. This can stimulate new and asymmetrical cartilage growth resulting in ‘cauliflower ear’.

Question 8

What is otitis externa?

Answer 8

Inflammation (redness and swelling) of the ear canal with discharge (usually self-limiting). If it becomes chronic, there is lots of oedema in the canal walls, narrowing the canal.

Question 9

What are the three layers of the tympanic membrane?

Answer 9

• Outer layer continuous with skin of EAC
• Middle fibrous layer
• Inner layers of resp epithelium (ciliated columnar epithelium with goblet cell)

Question 10

What structures are found in the middle ear?

Answer 10

• Tympanic membrane
• Ossicles
• Nerves

Question 11

What are ossicles?

Answer 11

Small bones of the middle that conduct sound waves from the tympanic membrane to the inner ear

Question 12

What condition can disrupt conduction through the ossicles?

Answer 12

Trauma or bony sclerosis (otosclerosis)

Question 13

What is the type of epithelium in the middle ear?

Answer 13

Ciliated columnar with goblet cells and therefore capable of producing mucous (glue ear)

Question 14

How does the middle ear connect to the mastoid system?

Answer 14

Via aditus to mastoid antrum

Question 15

How does the middle ear connect to the nasopharynx?

Answer 15

Via eustacian tube

Question 16

What nerves innervate the middle ear?

Answer 16

Facial nerve and it’s branch (chorda tympani)

Question 17

What are the anatomical relations of the middle ear?

Answer 17

• Meninges
• Middle cranial fossa
• Facial nerve
• Mastoid cavity
• Inner ear
• Sigmoid sinus/internal jugular vein

Question 18

What two conditions can affect the middle ear?

Answer 18

Otitis media and Cholesteatoma

Question 19

What can occur with otitis media?

Answer 19

Perforation can occur through the tympanic membrane if large enough pressure is built up

Effusion - presence of bubbles of gas, making it harder to equalise the ear

Question 20

What can be used to treat OM with effusion?

Answer 20

Grommets - small ventilation tube inserted in the eardrum to balance pressure on either side

Question 21

What is Cholesteatoma?

Answer 21

• Abnormal growth that develops behind the eardrum
• Nothing to do with cholesterol
• Skin in middle ear: keratinised squamous epithelium in wrong place
• Can be congenital or acquired
• Causes problems because they grow and are destructive

Question 22

What nerve innervates the upper half of the pinna?

Answer 22

Mandibular division of the trigeminal nerve (CN V3)

Question 23

What nerve innervated the lower half of the pinna?

Answer 23

Greater auricular nerve (C2, 3)

Question 24

What nerve innervates the anterior half of the external auditory canal?

Answer 24

Facial nerve (CN VII)

Question 25

What nerve innervates the posterior half of the eternal auditory canal?

Answer 25

Arnolds nerve (auricular branch of vagus nerve (CN X)

Question 26

What nerve innervates the middle ear?

Answer 26

Tympanic branch of the glossopharyngeal nerve (CN IX) –> Jacobsons nerve

Question 27

What is otalgia?

Answer 27

Ear pain

Question 28

What are secondary causes of otalgia wrt nerves that innervate the ear?

Answer 28

Referred pain:
• C2/3 – arthritis/cervical spondylosis, soft tissue injury
• CN V – Dental, TMJ dysfunction, nasopharyngeal disease
• CN IX – oropharyngeal inflammation/infection, tongue base malignancy
• CN X – laryngeal/pharyngeal malignancy

Question 29

What are the different structures of the inner ear?

Answer 29

• Bony and membranous labyrinth which contains fluid: perilymph and endolymph
• Cochlear: organ of corti (hearing organ)
• Peripheral vestibular apparatus: utricle, saccule, semicircular canals
• Vestibulocochlear nerve (CN VIII)

Question 30

Describe a simplified process of hearing

Answer 30

1. Function of middle ear is to transduce vibration into nervous impulses
2. Foot of stapes vibrates in oval window
3. Causes pressure waves through fluid filled cochlear
4. This is detected by hair cells in organ of corti
5. Transmitted to brainstem (junction of pons and medulla) by CN VIII

Question 31

What nerve is responsible to send signals to and from the ear and brain?

Answer 31

Vestibulocochlear nerve (CN VIII)

Question 32

What structures in the inner ear are important for balance?

Answer 32

• Semi-circular canals
• Saccule
• Utricle

Question 33

Why are the semicircular canals important for maintaining balance?

Answer 33

Detects head rotation

Question 34

What is the vestibule-occular reflex?

Answer 34

Its what makes you able to fix your visions on an object when your head is moving

Question 35

Why is the saccule important for maintaining balance?

Answer 35

Detect linear acceleration in vertical plane

Question 36

Why is the utricle important for maintaining balance?

Answer 36

Detects linear acceleration in horizontal plane