ear anatomy

Question 1

Three major areas of the ear

Answer 1

1. external (outer) = hearing only
2. middle (tympanic cavity) = hearing only
3. internal (inner) ear = hearing and equilibrium
   - receptors for hearing and balance respond to separate stimuli

Question 2

External ear (everything)

Answer 2

Auricle (pinna)

• helix (rim) and lobule (earlobe)
• funnels sound waves into auditory canal

External acoustic meatus (auditory canal)

• short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands
• transmits sound waves to eardrum

Tympanic membrane (eardrum)

• boundary b/t external and mid ears
• CT membrane that vibrates in response to sound
• transfers sound energy to bones of mid ear

Question 3

Middle Ear (Tympanic cavity) definition

Answer 3

• small, air-filled, mucosa-lined cavity in temporal bone
• flanked laterally by eardrum
• flanked medially by bony wall containing oval(vestibular) and round (cochlear) windows

Question 4

Middle ear parts

Answer 4

Epitympanic recess
mastoid antrum
pharyngotympanic (auditory) tube
-ossicles

Question 5

epitympanic recess

Answer 5

superior portion of middle ear

Question 6

mastoid antrum

Answer 6

canal for communication with mastoid air cells

Question 7

pharyngotympanic tube

Answer 7

• connects middle ear to nasopharynx

- equalizes pressure in middle ear cavity with external air pressure

Question 8

Ear ossicles

Answer 8

• 3 bones in tympanic cavity: malleus, incus, and stapes
• suspended by ligaments and joined by synovial joints
• transmit vibratory motion of eardrum to oval window

-tensor tympani (innervated by cranial nerve V) and stapedius muscles (innervated by cranial nerve VII) contract reflexively in response to loud sounds to prevent damage to hearing receptors

Question 9

otis media

Answer 9

• middle ear inflammation
• especially in kids
• shorter, more horizontal pharyngotympanic tubes
• most frequent cause of hearing loss in kids
• usually treated with antibiotics
• Myringotomy (ear tubes) to relieve pressure if severe

Question 10

Two major divisions of internal ear

Answer 10

Bony labrynth

• tortuous channels in temporal bone
• three regions: vestibule, semicircular canals, and cochlea
• filled with perilymph (similar to CSF)

Membranous labrynth

• series of membranous sacs and ducts
• filled with K-rich endolymph

Question 11

Vestibule

Answer 11

• central egg-shaped cavity of bony labrynth
• has 2 membranous sacs: saccule (continuous with cochlear duct) and utricle (continuous with semicircular canals)
• These sacs house maculae (equilibrium receptors) and respond to gravity/changes in positions of head

Question 12

Semicircular canals

Answer 12

• 3 canals (ant, post, and lat) that are 2/3 circles and lie in x,y,and z axes
• membranous semicircular ducts line each canal and communicate with utricle
• Ampulla of each canal houses equilibrium region called crista ampullaris
• receptor for dynamic equilibrium

Question 13

cochlea

Answer 13

• spiral, conical, bony chamber
• size of split pea
• extends from vestibule
• coils around bony pillar (modiolus)
• contain cochlear duct which houses spiral organ (organ of corti) and ends at cochlear apex

Question 14

chambers of cochlea

Answer 14

-cochlear cavity divided into 3 chanbers

• scala vestibuli = abuts oval window and has perilymph
• scala media (cochlear duct) = has endolymph
• scala tympani = terminates at round window and has perilymph

Scalae tympani and vestibuli are continuous with each other at helicotrema (apex)

Question 15

cochlear duct

Answer 15

• the “roof” is vestibular membrane
• external wall is stria vascularis –> secretes endolymph
• “floor” of cochlear duct composed of bony spiral lamina and basilar membrane which supports spiral organ
• cochlear branch of nerve VII runs from spiral organ to brain