The ear

Question 1

The external ear consists of…

Answer 1

Auricular cartilage
Scutiform
Annular cartilage
Bony acoustic process

Question 2

The middle ear consists of…

Answer 2

Tympanic cavity in tympanic bulla
Contains auditory ossicles
Connected to nasopharynx

Question 3

The inner ear is contained within the…

Answer 3

Petrous temporal bone

Question 4

What is the arterial and venous drainage of the external ear?

Answer 4

Auricular arteries (from internal carotid) and Venous drainage to internal maxillary vein

Question 5

The external ear is innervated by

Answer 5

Motor nerves to auricular muscles from the Auriculopalpebral branch of CN VII facial

Sensory innervation from the branch of CN V trigeminal and Cervical segmental C2

Question 6

What structures surround the external ear?

Answer 6

Surrounding the ear there are blood vessels (auricular artery, superficial temporal arteries, branches of external carotid artery and external maxillary vein) as well as nerves (facial nerve exits stylomastoid foramen passes rostroventral to horizontal canal and the auricolotemporal branch of mandibular portion of trigeminal nerve rostral to vertical canal)

Question 7

Can you pull the skin away on the ear?

Answer 7

The skin is tightly adherent esp on the concave pinna

Question 8

Describe the skin on the ear

Answer 8

thin, stratified keratinising epidermis
thin dermis containing adnexal structures, including hair follicles of various density and glands (sebaceous more prominent distally and apocrine (ceruminous) increased density proximally).

Question 9

How do the secretions from the ear change as you move proximally (closer to the skull)?

Answer 9

Sebaceous more prominent distally and apocrine (ceruminous) increased density proximally so this means that the secretions lower down the ear are more watery and as you go up the ear the secretions become more waxy and lipid dense.

Question 10

What does cerumen contain?

Answer 10

Exfoliated cells
Sebaceous secretions with high lipid content
Immunoglobulins IgA, IgG, IgM but perdominantly IgG

Question 11

What is epithelial cell migration and why does it occur?

Answer 11

Epithelial cells move laterally from the centre of the TM to the periphery. Then desquamate to contribute to production of cerumen.
Epithelial migration helps transport cerumen to superficial (ie distal) portion of ear canal to remove cerumen and debris

Question 12

What could happen to the epithelial cell escalator in disease?

Answer 12

This mechanism may be impeded in diseased ears and exudate not removed naturally

Question 13

What is the tympanic membrane?

Answer 13

This is an epithelial structure that forms a boundary between external and middle ear

Question 14

Describe the sandwich structure of the tympanic membrane?

Answer 14

Stratified keratinising epithelium laterally
Thin lamina propria which contains collagen bundles in the middle
And a Cuboidal mucosal epithelium medially (middle ear side) with scattered secretory goblet cells

Question 15

How do cells migrate in the tympanic membrane?

Answer 15

Migration of cells centripetally from middle at level of stratum granulosum

Question 16

Which part of the tympanic membrane should be translucent?

Answer 16

Thinner pars tensa ventrally which should be translucent in healthy animal

Question 17

What shape is the malleus when viewed with an otoscope and what is it associated with?

Answer 17

When visualised the manubrium of malleus visible, it is C-shaped and closely associated with collagen in lamina propria

Question 18

What do you look at ears with?

Answer 18

An otoscope

Question 19

What are the three compartments of the middle ear?

Answer 19

Epitympanum: dorsal, smallest, contains auditory ossicles malleus and incus

Mesotympanum: Tympanic membrane laterally, bony promontory medially, contains 3rd ossicle stapes attached to oval window, round window and opening to auditory tube

Hypotympanum or fundus contains the tympanic bulla

Question 20

In cats is there communication between the mesotympanum and the hypotympanum?

Answer 20

There is an incomplete bony septum.

Question 21

Name the auditory ossicles

Answer 21

Malleus, Incus and Stapes

Question 22

The middle ear is lined with a different epithelium to the rest of the ear, what is it?

Answer 22

Cuboidal to columnar epithelial lining of mucosal origin containing secretory goblet cells

Question 23

Where does the auditory tube/Eustachian tube run?

Answer 23

¥ runs dorsolateral/ventromedial to nasopharynx

Question 24

What is the auditory tube/Eustachian tube lined by?

Answer 24

pseudostratified, ciliated, columnar epithelium (density of goblet cells increases towards nasopharynx)

Question 25

Why does the auditory tube/Eustachian have goblet cells?

Answer 25

More prominent at tympanic cavity end, have surfactant secretion to keep tube patent (lecithin, lipids, mucopolysaccharides)

Question 26

Branches of facial and vagus nerve form the tympanic nerve, where does this nerve run?

Answer 26

Traverses tympanic bulla cavity to lingual nerve + pre-ganglionic parasympathetic fibres to salivary glands

Question 27

Where do the Post-ganglionic fibres of cervical sympathetic trunk run?

Answer 27

Runs in dorsomedial wall of tympanic cavity and in cat runs in dividing septum
(joins CN IV to eye)

Question 28

Where does the CVII run?

Answer 28

Enters petrosal bone through internal acoustic meatus (with VIII) and runs inside the facial canal. It has an intermediate component that branches off inside the bone (forms greater petrosal nerve, stapedial motor nerve and chorda tympani) and the rest of the nerve emerges through the stylomastoid foramen.

Question 29

What does the inner ear consist of?

Answer 29

This consists of the Cochlea, Vestibule, Semicircular canals

Encased in bony labyrinth of petrous temporal bone

Question 30

What is malassezia spp?

Answer 30

Monopolar budding yeasts found in the ears of cats and dogs

Malassezia pachydermatis: Non-lipid dependent, broad based budding organisms.

Question 31

How doe we take cytology of the external ear?

Answer 31

Samples taken with sterile cotton bud and rolled onto slide then Heat fixed and stained with DiffQuick or RapiStain
Oil immersion usually not necessary.