Chapter 20 Ear Flashcards
Pinna (auricle)
functions to collect sound
Primary parts of ear
helix (rim) & tragus
Skin of auditory canal innervated by…
CN X
In auditory canal?
- ceruminous glands
- sebaceous glands
- hairs
Tympanic membrane
- ear drum
- 2 layers
External auditory canal
cartilage + meatus (bone)
TMD=
TMJ dysfunction (shared nerves)
Middle ear
outer ear/ear drum + pharynx + mastoid sinus + inner ear
Squamous portion
thin
Petrosal portion
massive
What is stretched across external auditory canal?
ear drum
Auditory ossicles
malleus, incus, stapes
What do the auditory ossicles do?
carry vibrations from ear drum > oval window
Tensor tympani muscle attaches to…
malleus
Stapedius muscle attaches to…
stapes
Tympanic reflex
- tension on ear drum
- stapedius “locks-down” the ossicular chain= dampens loud sounds
Auditory (eustachian) tube
- connects middle-ear to pharynx
- equalizes pressure across tympanic membrane
Inflammation to the auditory tube
- infectious material trapped in middle ear
- fluid builds up and pressure
- threatens ear drum & hearing/balance
Change in pressure =
change in altitude
Myringotomy
- tubes that perforate the ear drum
- releases fluid from middle ear
Labyrinthitis
infection of inner ear
Embryo jaw muscle & nerve
tympani m. V3
Adult jaw muscle & nerve
Masseter, etc V3
Hyoid arch muscle & nerve
stapedius m. VII
Osseous labyrinth
- -boney canals in petrous portion of the temporal bone
- membranous labyrinth is housed w/in the boney labyrinth
Membranous labyrinth
-hollow tubes within osseous labyrinth
Endolymph
fills each canal/chamber
Perilymph
space btw oss. & memb. labyrinths
Hair cell
- hearing & equilibrium
- located throughout membranous labyrinth
- vibration/movement of stereocilia = signal (VIII)
Ampullae
- swelling at base of canal
- hair cells aligned in ridge = crista
Cupula
- tips of hair cells embedded in gel
- distorted by endolymph movement = sensitive to changes in position
Sound
vibration of air molecules
High-pitched tones
- high frequency
- short wave-lengths travel short distances
- pin-drop
Low-pitched tones
- low frequency
- long wave-length travel long distances
- truck
Hearing ability
determined by body size
Cochlea
Region of inner ear responsible for hearing
Cochlear duct
- coiled tube resembling a snail’s shell
- part of the membranous labyrinth
Basal membrane
floor of cochlear duct
Cochlear duct lies btw two other ducts
vestibular duct & tympanic duct
Vestibular duct
- oval window to the helicotrema
- filled with perilymph
Tympanic duct
- helicotrema to the round window
- filled with perilymph
Helicotrema
- helical extremity
- tip of cochlea
Oval window membrane
vestibular duct
round window
tympanic duct
Organ of Corti
- auditory receptor
- tips of hair cells in contact with tectorial membranes
- signal > cochlear part of CN VIII
Sound transduction
- sound vibrates the ear drum which vibrates ossicles
- stapes oscillates within the oval window
- membrane vibrates the perilymph in vestibular duct
- vibrations go around helicotrema into tympanic duct
- pressure causes round window to bulge outwards
Perilymph in vest/tymp ducts…
distorts the basal membrane
Problem with hair-cells
generic in size, shape, and function
Place-theory
- sweet-spot along BM
- combination of wave-length/location= sound
Basilar membrane is ribbon-like
- thick/stiff at the base
- thin/floppy @ helicotrema
High pitch/short wavelengths/short distance
base of BM
Low pitch/long wavelength/long distance
tip of BM
