Ear

Question 1

The ear is split into 3 sections

Answer 1

The external ear
Middle ear
Inner ear

Question 2

What is the pinna and whats it made of?

Answer 2

Also called the auricle, its the visible part of the ear residing outside the head.

Its made of elastic cartilage and covered in stratified keratinized epithelium (skin)

Question 3

Describe the lateral 1/3rd of the external ear canal?

Answer 3

Its made of skin and cartilage like the auricle.

It has ceruminous and sebaceous glands that produce wax

Question 4

What is the function of the lateral 1/3rd of of the external ear canal and wax?

Answer 4

The lateral 3rd acts as a protective/disinfectant barrier.

Skin gets trapped here in the wax and sheds as a cleaning mechanism

Question 5

How serious is an external ear obstruction?

Answer 5

Wax or other mechanical obstruction have a minimal effect on hearing loss compared to middle or inner ear problems

Question 6

What is the tympanic membrane?

Answer 6

A triple layered membrane dividing the external ear canal and the middle ear

Question 7

Layers of the tympanic membrane?

Answer 7

Outer layer - Continuous with the skin of the EAC, in fact its grows out from the umbo at the centre of the tympanic membrane

Middle layer - Fibrous

Inner Layer - resp. epithelium (Ciliated Columna Epithelium + Goblet Cells)

Question 8

What can you see through the tympanic membrane?

Answer 8

Handle of the malleus

Question 9

What are the important parts of the middle ear?

Answer 9

The 3 ossicles:

• Small bones that carry sound from the tympanic membrane -> Inner ear
• Malleus -> Incus -> Stapes
• The stapes foot plate sits against the oval window through to the inner ear

The chorda Tympani comes from the facial nerve and loops around the short process of the malleus.

Question 10

Describe the epithelium of the middle ear?

Answer 10

Respiratory!

Ciliated Columnar Epithelium + goblet cells

Question 11

What are the connections of the middle ear?

Answer 11

Mastoid air cells

Nasopharynx via eustachian tube

Question 12

Whats the clinical relevance of the middle ear?

Answer 12

• The ossicles can be damaged by trauma or osteosclerosis
• Otitis media
• Cholesteatoma

Question 13

What is a cholesteatoma?

Answer 13

An invasion of keratinized squamous epithelium through the tympanic membrane into the middle ear

Question 14

What are the important relations of the middle ear?

Answer 14

• Middle Cranial Fossa
• ICA
• Sigmoid Sinus
• IJV
• Meninges
• Facial Nerve
• Mastoid Cavity
• Inner Ear

Question 15

What are the segments of the facial nerve?

Answer 15

6:

• Intracranial
• Meatal (passing through the internal auditory meatus)
• Labyrinthine segment
• Tympanic Segment
• Mastoid Segment
• Extratemporal segment (section outside the stylomastoi foramen)

Question 16

What does the facial nerve do?

Answer 16

• Innervates muscles of facial expression
• Special sensory innervation to the ant 2/3rds of the tongue via the chorda tympani
• Parasympathetic innervation of the submandibular/sublingual salivary glands

Question 17

What makes up the inner ear?

Answer 17

A bony and membranous labyrinth creating sections called the scali vestibuli, tympani & media.
They contain perilymph and endolymph.

Also the organ of corti whch contains hair cells that connect to the cochlear nerve

Also the peripheral vestibular apparatus

Question 18

How does hearing occur in terms of the inner ear?

Answer 18

Vibration of stapes

• > Transmitted through oval window
• > Produces pressure waves in cochlear fluid
• > Detected by hair cells in organ of corti
• > Transmitted to brainstem via cochlear nerve -> Vestibulocochlear nerve (CN VIII)

Question 19

What is the peripheral vestibular apparatus?

Answer 19

Utricle: Detects linear Horizontal Acceleration

Saccule: Detects Linear Verticle Acceleration

Semicircular Canals:

• Detect head rotation
• Responsible for vestibulo-ocular reflux

Balance info is then transmitted to the brainstem by the Vestibulocochlear nerve (Cr N 8)

Question 20

What is the vestibulo-ocular reflex?

Answer 20

The ability to fix vision on an object when the head is moving

Question 21

What are the key nerves of the ear?

Answer 21

• Trigeminal Mandibular branch (CN V3) supplies pinna
• Facial nerve innervates anterior 1/2 of EAC
• Arnolds nerve is the auricular branch of the vagus and innervates the posterior half of the EAC
• Jacobsons nerve is the tympanic branch of the glossopharyngeal nerve and supplies the middle ear along with the chorda tympani (branch of CN 7)

Question 22

Why is shared innervation by different parts of the face/head important?

Answer 22

Otalgia can occur with no obvious ear cause, i.e. it may be referred