the normal ear Flashcards
what structures encompas the external ear
pinna, external ear canal (external auditory meatus) down to the tympanic membrane
what structures encompass the middle ear
- tympanic cavity in tympanic bulla
- contains auditory ossicles
- connects to nasopharynx
the inner ear holds which structures
structures within petrous temporal bone
describe the cartilagenous structures of the external ear
- 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)
discuss vascular supply and innervation of the external ear
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
what structures will you find adjacent to the external ear?
- parotid salivary gland
- blood vessels
- nerves
label
what makes up secretions of the ear canal
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)
what is the purpose of the cerumen (ear wax)
provides protective and antimicrobial layer to the ear
describe how exudate in the ear is carried to the surface
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
describe the microscopic structure of the tympanic membrane
- epithelial structure
- stratified squamous keratinising epithelium laterally
- thin lmaina propria
- simple squamous/cuboidal mucosal epithelium medially (includes scattered secretory goblet cells)
decrbe the gross description of the tympanic membrane
- 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
label green arrows
name the 3 compartments of the middle ear
- 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
describe the epithelium of the middle ear and associated structures
- 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
