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 99.9% of sound waves would bounce off the oval window This energy reflected off oval window gives about a 30 dB hearing loss 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 IMPEDANCE – the resistance to flow of energy

Two Forms of Impedance ResistanceReactance Stiffness Stiffness Mass Mass

Area Advantage TM OW

Lever Advantage

Area & Lever Ratio 17 * 1.3 = _______ therefore the overall increase in pressure equals: 20 Log 22 = _________________ 20 Log 22 = _________________ 22 to dB or 27 dB

The Acoustic Reflex

STAPEDIUS vs. TENSOR TYMPANI STAPEDIUS vs. TENSOR TYMPANI 6 mm in length 6 mm in length Arises in bony canal Arises in bony canal adjoining the facial canal adjoining the facial canal and inserts on the head and inserts on the head of the stapes of the stapes Cranial Nerve VII Cranial Nerve VII Activates by acoustic Activates by acoustic (acoustic reflex) and (acoustic reflex) and nonacoustic means nonacoustic means 25 mm in length 25 mm in length Arises from wall of Arises from wall of Eustachian tube and Eustachian tube and inserts on the upper inserts on the upper margin of the margin of the manubrium of malleus manubrium of malleus Cranial Nerve V Cranial Nerve V Activates by startle Activates by startle response and/or tactile response and/or tactile stimulation of the stimulation of the orbital area orbital area

Neuronal Organization of Acoustic Stapedius Reflexes

Clinical Acoustic-Reflex Protocols Acoustic-reflex thresholds AR thresholds vs. auditory thresholds AR thresholds vs. auditory thresholds Reduction of dB per dB Reduction of dB per dB INPUT INNER EAR 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