Lecture Outline #20: Special Senses: Ear

Question 1

ear

Answer 1

a series of mechanical transducers

Question 2

external ear

Answer 2

auricle/pinna - collects sound and directs in into canal
tragus
helix
auditory canal (skin/cartilage) and external acoustic meatus (opening in bone) - skin is innervated by mainly X - little VII & V3, contains ceruminous glands, sebaceous glands, and hairs. Also contains tympanic membrane [epithelium 2 layers and separates external and middle ear (lateral side innervated by X, VII, V3 and medial by IX)] and external auditory canal (cartilage & meatus)

Question 3

middle ear boundaries

Answer 3

lateral - tympanic membrane collects sound waves
medial - bony wall separating mid from inner ear
superior - petrous portion of temporal bone
posterior - pneumatized (mastoid antrum)
anterior - opening of the Eustachian tube

Question 4

auditory ossicles

Answer 4

malleus, incus, stapes
carry vibrations from ear drum to oval window
suspended/connected by ligaments/muscle
- tensor tympani m. attaches to malleus, chorda tympani n. (V3)
- stapedius m. attaches to stapes (VII)

Question 5

tympanic reflex

Answer 5

tensor tympani places tension across eardrum
stapedius m. locks down ossicular chain
= dampens vibrations from LOUD noises

Question 6

ear pressure

Answer 6

wants equal pressure in external & middle ear = pops

Question 7

Eustachian tube

Answer 7

connects middle ear to pharynx
tube is supported by m.s & cartilage
equalizes pressure across tympanic membrane

Question 8

inflammation/damage of Eustachian tube

Answer 8

if inflamed, will swell shut and infectious bacteria will be trapped in middle ear, fluid build up = pain
threatens ear drum & hearing/balance

Question 9

myringotomy
mastoiditis
otitis media
labyrinthitis

Answer 9

insertion of a tube that perforates the ear drum to release fluid/pressure from the middle ear
M: infection of mastoid air cells = mastoid bone of temporal bone
OM: infection of middle ear
L: infection of inner ear

Question 10

inner ear labyrinths & lymphs

Answer 10

osseous labyrinths - bony canals in petrous portion
membranous labyrinth - hollow tubes and chambers within osseous.
endolymph - within mem. lab. fills each tube/chamber, bathes stereocilia, high in potassium, produced by stria vascularis
perilymph - fills in space between oss. & mem. labyrinths, ~CSF, doesn’t mix with endolymph

Question 11

hair cells

Answer 11

functional unit of hearing & equilibrium
located throughout mem lab., bathed in endolymph
vibration/movement of this = VIII signal
is VIII source

Question 12

semicircular canals

Answer 12

three - filled with endolymph
each canal has an no innervated, osseous swelling @ base = ampulla
each ampulla has crista - hair cells align in a ridge
crista is embedded in cupula - gel-like structure (when moving, fluid pushed on cupula and bends crista, sending electrochemical signal to brain that movement is happening.

Question 13

utricle & saccule

Answer 13

each has a macula - swellings of osseous mem., have hair cells covered in gel. Gel is covered w/ CaCO3 crystals called otoliths.
u - linear accel or deaccel, otoliths slide forward/backward, bending stereocilia
s - gravity, up & down, otoliths push down or rise on macula, bending stereocilia

Question 14

vertigo

Answer 14

1. receptor overload/miscommunication
   - steady movement induces endo to flow
   - flow can be interrupted by abrupt stop/change
   - dizziness & nausea
2. mismatch of audio/visual info (seasickness)
   - vestibular apparatus senses movement
   - visual system says stationary
   - vestibular nuclei in BS is confused
   - dizziness & nausea

Question 15

vertigo & vestibular nystagmus

Answer 15

steady movement induces endo to flow
- if continues - endolymph stabilizes/stops and eyes adjust to tracking of moving objects
- if sudden stop - endolymph is re-accelerated, eyes will race in direction of spin = nystagmus, continues until endo settles

Question 16

sound

Answer 16

vibration of air molecules
high pitched tones - high frequency vibration = short wave-lengths = travel short distances
low pitched tones - low frequency vibrations = long wave-lengths = travel long distances
Air (thru external acoustic meatus) - solid (ossicles) - liquid (endolymph)

Question 17

hearing

Answer 17

ability - size of pinna, tympanum, ossicles, cochlear
20-20000 Hz

Question 18

cochlea - membranes and duct

Answer 18

cochlea - region of inner ear responsible for hearing
cochlear duct - coiled tube, part of mem. labyrinth with endolymphatic deep
basal membrane - floor of cochlear duct
tectorial membrane - stimulate hair cells/organ of corti when vibrations come through

Question 19

cochlear - ducts

Answer 19

vestibular duct - oval window to helicotrema
tympanic duct - helicotrema to round window
both filled w/ perilymph
helicotrema - tip of cochlea

Question 20

organ of corti

Answer 20

hair cells - disturbed along basal membrane
tips in contact with tectorial membrane
adjacent with mem. labyrinth in cochlea

Question 21

sound transduction

Answer 21

auricle/pinna - external acoustic meatus - tympanic membrane - malleus - incus - stapes - oval window - vestibular/tympanic ducts - cochlear duct - basilar membrane & stereocilia

Question 22

place theory

Answer 22

each wavelength has a sweet spot along basal membrane
high pitch - base of BM by windows
low pitch - tip of BM, by helicotrema

Question 23

tinnitis

Answer 23

constant ringing/buzzing
damage to hair cells @ high frequencies