Middle ear

The auditory system is divided into the external ear, the middle ear and the inner ear. The middle ear consists of the tympanic membrane (TM) and three ossicles, namely, the malleus, the incus and the stapes, respectively. The stapes footplate is attached to the base of the cochlea. These ossicles are supported by many ligaments.
Human auditory system	Middle ear

When an acoustic sound goes into the external ear canal, it vibrates the TM. The vibration is then transmitted to the cochlea via the ossicles. Therefore, the middle ear plays an important role that converting the sound to the mechanical vibration. If you shout something at a swimmer who is under the water, he cannot hear the sounds, because almost all the sounds are reflected on the surface of the water. The cochlea is fulfilled with the lymph fluid. Therefore, if there are not the ossicles in the auditory system, the sound cannot be transmitted to the cochlea. However, in fact, because of lever effect of the ossicles and the ratio of the area of the TM to that of the stapes footplate, the sound can be transmitted to the cochlea effectively.

(i) Dynamic behavior of the middle ear
As diseases of the middle ear affect the vibration mode of the TM, it is necessary for a correct diagnosis to measure the TM vibration precisely. However, it is very difficult to measure the TM vibration, because the vibration amplitude of the TM is only several dozen nanometer even when the sound pressure level of 80 dB (loud voice) is applied to the TM. Therefore, we developed a measurement system which can measure the vibration mode of the TM using time-averaged electronic speckle pattern interferometry(ESPI). In addition, we developed a three-dimensional sweep frequency impedance meter (SFI), which can diagnose the middle-ear diseases and an apparatus for diagnosis of the ossicular mobility, which can quantitatively evaluate the ossicular mobility.

(ii) Computer simulation
It is very important to measure the vibration of the ossicles. However, it is difficult to measure its vibration, because the ossicles cannot be seen directly. In our laboratory, the FEM model of the middle ear has been established and the dynamic behavior of the middle ear is analyzed.

　