Midterm Flashcards
parts of the outer ear (3)
- pinna
- External Auditory Meatus
- Lateral Layer of TM
Middle Ear
- Ossicles
- Muscles- Acoustic Reflex
- Eustachian Tube
- Where acoustic energy converts to mechanical energy
- Impedance Mismatch
Parts of Ossicles
- Maleus
- Incus
- Stapes
muscles of middle ear involved in acoustic reflex
- stapedius (7th cn)
- Tensor Tympani (5th cn)
Eustachian Tube
- middle ear
- clear excess mucous
- equalize middle ear pressure
Impedance Mismatch
- middle ear
- ossicles act as a lever system
- reduction in area from the TM to oval window, increasing force
Inner Ear
Balance
Hearing
Balance in the inner ear
- vestibule (linear acceleration)
- semicircular canals (rotational)
Hearing in inner ear
Cochlea-organ of hearing
Cochlea
- where mechanical energy converts to electrical energy
- membranous labyrinth encased in temporal bone
- Modiolus
- Osseous Spiral Lamina
- Basilar Membrane
- Reissner’s Membrane
Modiolus
central axis of cochlea
Osseous Spiral Lamina
shelf-like structure protecting from modiolus
Basilar Membrane
projects from spiral lamina and connects to outer wall of cochlea, the spiral ligament referred to as floor of cochlea
Reissner’s Membrane
projects from spiral lamina in an upward fashion to a region of outer wall (ceiling)
Channels of the Cochlea
- Scala Vestibuli (Above Reissner’s)
- Scala Tympani (Below Basilar’s)
- Scala Media/ Cochlear Duct- btwn Reissner’s and Basilar’s, organ of corti
Organ of Corti
- sensory organ of hearing
- rests on floor of BM
- sensory cells
Sensory Cells of Organ of Corti
- Inner: single row, towards modiolus “U” shape, loud sounds
- Outer: 3-4 rows, towards spiral lamina, “v/w” shape, soft sounds
- Stereocili: project from both IHC & OHC, graded in length
- Tectorial Membrane: longest stereocilia are embedded in it.
Pathways of Sound
- Conductive: outer & middle ear
- Sensory/Neural: inner ear & auditory nerve
Conduction of Sound
Air
Bone
Air Conduction
- sound travels through all 3 parts of ear: outer, middle, & inner
- how we hear in every day life
Bone Conduction
- occurs through vibrating the skull
- sound BYPASSES outer & middle ear to directly stimulate nerve/inner ear
Measurement of Hearing
Volume: Decibel (dB)
Pitch: Frequency (Hz)
Air vs. Bone Conduction
- determines type of HL
- Air-Bone gap: difference of 15 dB or more btwn 2 methods of testing
- separates conductive HL vs. mixed vs. sensorineural
Types of HL
- Conductive
- Sensorineural
- Mixed
Conductive HL
- problem exists w/in conductive/mechanical portion of ear (outer &/or middle ear)
- Air conduction-impaired
- Bone conduction- normal
- Air-Bone Gap Present**
SNHL
- problem lies w/in inner ear &/or nerve
- Mechanical/Conductive portion- normal
- Air Conduction- impaired
- Bone Conduction- impaired
- Air & Bone are EQUALLY impaired- NO AIR-BONE GAP
Mixed HL
- damage occurs to both conductive & sensory/ neural pathways
- air conduction- impaired
- bone conduction- impaired, but BETTER THAN AIR
- Air-Bone Gap Present
- age related HL, but cerumen impaction
- congenital HL, but patient developed an ear infection
Cross Hearing
-when sound presented on 1 ear is so loud it sets skull into vibratory state, causing cochlea on other side to vibrate (bone conduction)
Masking
- presenting 2 sounds at same time, where intensity of one causes other to be inaudible
- shifts threshold- a sound now needs to be louder to detect
- masker- noise that causes change of threshold, usually presented to better ear or ear you do not want a response from
- eliminating an ear to contribute to a response
Test ear vs. non test ear
- TE- ear you are testing/want response to come from this side
- NTE- ear you are eliminating, masker presented to this side
Interaural Attenuation
- Loss of energy from one side, but picked up from other side
- energy transferred from TE to NTE
- level at which sound will cause bone conduction/ IA
a. headphones = 40 dB
b. inserts = 70 dB
c. bone oscillator = 0 dB
When do we need Masking?
- Air Conduction:
a. large difference btwn ears
b. Headphones: difference of 40 dB
c. Inserts: difference of 70 dB - Bone Conduction:
a. air-bone gap present
b. unmasked bone only tests better cochlea, should a difference exist
c. Thus, when BC is better than AC (air-bone gap) we do not know which ear is responding
Formula for masking
AC te - IA > BC nte
Masking noises used
- Pure tone testing: narrowband noise
2. speech audiometry: speech noise
Pure tone testing & SRT/SAT
- in general you need about 30 dB of noise above AC threshold of NTE
- AC threshold NTE= 30 dB, you need to present masking at 60 dB
- Before you reach full 30 dB above NTE, start using Plateau method first bc some will require more than 30 dB
WRT scores
- present noise 20 dB less than that of presentation level in TE
- Exp. Presenting words at 70 dB in TE requires 50 dB of speech noise in NTE
- Note: some situations may require more noise