the normal ear

Question 1

what structures encompas the external ear

Answer 1

pinna, external ear canal (external auditory meatus) down to the tympanic membrane

Question 2

what structures encompass the middle ear

Answer 2

• tympanic cavity in tympanic bulla
• contains auditory ossicles
• connects to nasopharynx

Question 3

the inner ear holds which structures

Answer 3

structures within petrous temporal bone

Question 4

describe the cartilagenous structures of the external ear

Answer 4

• auricular cartilage of the ear flap is flattened distally, ridged to form anthelix medially and tragus laterally and forms a cone shaped tube proximally (choncha)
• annular cartilage fits within the base of the conchal tube of the auricular cartilage and has ligamentous attachments to bony acoustic brocess (internal auditory meatus) of temporal bone of skull
• scutiform cartilage within muscles rostromedial to canal to provide support (not part of ear canal)

Question 5

discuss vascular supply and innervation of the external ear

Answer 5

vascular supply: auricular arteries (from internal carotid) and drains to internal maxillary vein
innervation: motor nerves to auricular muscles by auriculopalpebral branch of facial nerve and sensory from branch of trigeminal AND cervical degments of C2

Question 6

what structures will you find adjacent to the external ear?

Answer 6

• parotid salivary gland
• blood vessels
• nerves

Question 7

label

Answer 7

Question 8

what makes up secretions of the ear canal

Answer 8

secretion of the ear canal comprised of:
- exfoliated cells
- sebaceous secretions (high lipid content of various classes)
- ceruminous gland secretions (more aqueous)
- immunoglobulins (predominently IgG)

Question 9

what is the purpose of the cerumen (ear wax)

Answer 9

provides protective and antimicrobial layer to the ear

Question 10

describe how exudate in the ear is carried to the surface

Answer 10

epithelial cell migration:
- epithelial cells move laterally from the centre of the tympanic membrane to the periphery, then desquamate to contribute to production of cerumen
- epithelial migration helps transport cerumen to superficial portion of ear canal and therefore removes cerumen and debris from the ear canal

Question 11

describe the microscopic structure of the tympanic membrane

Answer 11

• epithelial structure
• stratified squamous keratinising epithelium laterally
• thin lmaina propria
• simple squamous/cuboidal mucosal epithelium medially (includes scattered secretory goblet cells)

Question 12

decrbe the gross description of the tympanic membrane

Answer 12

• visible otoscopically from the external cana in dg and cat (limited in horse)
• thicker pars flaccida dorsoventrally (adjacent to edge of malleus)
• thinner pars tensa ventrally (larger than pars flaccida and should be translucent in a healthy animal)
• manubrium of malleus visible as a C shaped structure pointing rostrally

Question 13

label green arrows

Answer 13

Question 14

name the 3 compartments of the middle ear

Answer 14

• epitympanum dorsally containing auditory ossicles (malleus and incus)
• mesotympanum (lateral to tympanic membrane) includes stapes attached to oval window and round window and opening of auditory tube
• hypotympanum or fundus

Question 15

describe the epithelium of the middle ear and associated structures

Answer 15

• simple squamous to cuboidal lining
• pharyngeal mucosal origin
• contains secretory goblet cells
• in the eustachian tube, pseudostratified, ciliated columnar epithelium with density increasing towards nasopharynx
• scattered goblet cells more prominent at tympanic cavity end
• surfactant keeps tube patent

Question 16

what structures are adjacent to the middle ear

Answer 16

• facial nerve: in facial canal in petrous temporal bone, exposed in dorsal cavity then exits stylomastoid foramen)
• branches of facial and vagus nerve (forms tympanic nerve)
• post ganglionic fibres of cervical sympathetic trunk

Question 17

describe the topographical course of facial nerve as it relates to the middle ear

Answer 17

• enters petrous temporal bone through internal acoustic meatus with vestibulocochlear
• runs inside the facial canal
• intermediate component enters tympanic cavity near oval window
• 3 fibres then branch off (greater petrosal nerve, stapedial nerve and chroda tympani nerve)
• emerges through stylomastoid foramen

Question 18

what are some normal microflora of the external ear

Answer 18

• staphylococcus
• malassezia pachydermatis