Transcript The Acoustic Reflex - Brigham Young University

The Lever Ratio
Purpose of ME
To transmit sound energy from the air
space in the EAC to the fluid in the
cochlea
This is accomplished by vibration of the
ossicles
So what if we didn’t have a TM
or any ossicles?
99.9% of sound waves would bounce off the
oval window
This energy reflected off oval window gives
about a 30 dB hearing loss
Purpose of the TM and the ossicles -- eliminate
IMPEDANCE MISMATCH
IMPEDANCE – the resistance to flow of energy
Two Forms of Impedance
Resistance
Reactance


Stiffness
Mass
Area Advantage
TM
OW
Lever Advantage
Area & Lever Ratio
17 * 1.3 = _______
22 to 1
therefore the overall increase in pressure equals:
26.84 dB or 27 dB
20 Log 22 = _________________
The Acoustic Reflex
STAPEDIUS vs.
• 6 mm in length
•
Arises in bony canal
adjoining the facial canal
and inserts on the head
of the stapes
TENSOR TYMPANI
• 25 mm in length
• Arises from wall of
Eustachian tube and
inserts on the upper
margin of the
manubrium of malleus
• Cranial Nerve VII
• Cranial Nerve V
• Activates by acoustic
(acoustic reflex) and
nonacoustic means
• Activates by startle
response and/or tactile
stimulation of the
orbital area
Neuronal Organization of
Acoustic Stapedius Reflexes
Clinical Acoustic-Reflex Protocols
Acoustic-reflex thresholds


AR thresholds vs. auditory thresholds
Reduction of .6 - .7 dB per dB
INPUT
INNER EAR
80
80
81
80.3 - 80.4
90
83 - 84
95
84.5 - 86
108
88.4 - 91.2
We only measure up to 110 dB HL
Acoustic Reflex Profiles in
Specific Pathologies
Middle ear disorders
Facial nerve disorders
Cochlear disorders
Eighth nerve disorders
Central (Brainstem) disorders