The mechanisms described above become obvious when one studies the transference function of the ME, ie the complex interaction between amplitude and phase that exists between the acoustic pressure at the entrance to the inner ear (Pv: pressure within the perilymph at the base of the scala vestibuli) and the pressure at the TM (Pt): Pv/Pt. This along with clinical experience leads some researchers to report that TTTS symptoms can be reduced or eliminated once sound tolerances improve and anxiety to protect one’s ears is reduced. More about physics (s ee below) Middle Ear transfer function Both middle-ear muscles receive direct control from centers of the brain that are influenced by emotional state (the serotonergic system) (McFerran 2007).
In effect, ME function (similar to any type of mechanical system) depends on the friction (R) of the ossicular joints, the mass of the drum/ ossicular chain, and the rigidity (K) of the various membranes, ligaments, air volume and so on.
Because of the relationship between the surface areas of the TM (area S1 = 0.6 cm2) and the stapes footplate (area S2 = 0.03 cm2), and because of the interaction of the ME levers (the axis of the ossicular chain passes very close to the incudomalleolar joint, but the two arms of this lever are of unequal length, d1/d2 = ~ 1.3), the pressure amplification is theoretically in the order of x26 (approx 28 dB)īeware, however! This calculation must be used with caution, because, due to its mechanical characteristics, the behaviour and the efficiency of the ME varies greatly with varying frequency of sound (f).
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