The fusimotor system controls joint muscles for tension, balance, and coordination of the joint movements (feedback regulation) (Roll et al. 1989). Like any other skeletal muscle, middle ear muscles (i.e., tensor tympani and stapedius)
possess muscle spindles (five on average) as well as a fusimotor system (one to three intrafusal fibers) (Kierner et al. 1999). Conceivably, high acoustic pressures of firearms could cause, besides hearing loss, stretch/contraction Inhibitors,research,lifescience,medical microlesions on muscles and joint tendons of the middle ear due to exaggerated acoustic reflexes, with resulting deleterious effects on fusimotor system of middle ear muscle spindles, and proprioception dysfunction. Action Inhibitors,research,lifescience,medical of middle ear muscles was required for the auditory task in the MRI noisy environment. Movement preparation or achievement probably triggers widespread muscle tone response, which may account for a sensitizing effect of the motor activity involved in “target” conditions, in revealing middle ear proprioceptive anomalies in AAT patients. The emotional and sensorimotor anomalies associated with AAT may
be aggravating co-factors, ultimately generating abnormal physical constraints along the tympano-ossicular chain through, for instance, tension in the temporo-mandibular region (Allin 1975; Al–Ani and Gray 2007). Additionally, anxiety and stress activate the sympathetic system that Inhibitors,research,lifescience,medical innervates the muscle spindles (Nozzoli et al. 1987). The relative importance of mechanical dysregulation or of emotional hyperreactivity Inhibitors,research,lifescience,medical in middle ear proprioceptive dysfunction is a matter
of conjecture and may vary from subject to subject. In general, proprioceptive dysfunction causes mild find more confusion and a reduction of the accuracy of task performance (Verschueren et al. 1999) that may also explain the differences in performance observed between AAT and control groups during the behavioral task. Inhibitors,research,lifescience,medical Our results led us to envisage besides an emotional disturbance, the possibility of a relationship between middle ear proprioceptive dysfunction and tinnitus in AAT subjects. Mechanistic origin of tinnitus The mechanistic origin of tinnitus is still a matter of debate. Cochlear cell damage (Liberman and Dodds 1987) is widely considered as a most likely origin for AAT tinnitus. It is widely assumed that cochlear Tolmetin cell damage triggers changes in the central auditory system, which is then interpreted as tinnitus by the higher processing stages in the brain (Jastreboff 1990; Roberts et al. 2010). Thus, hyperactivity and synchronization of neural firing in the dorsal cochlear nucleus, inferior colliculus or the auditory cortex in acoustic traumas has been reported (Rajan and Irvine 1998; Kaltenbach 2000; Eggermont 2003, 2006; Norena and Eggermont 2003) and attributed to an imbalance of exitability between the cochlear inner hair cells (IHC) and the outer hair cells (OHC) (Jastreboff 1990; Shiomi et al. 1997; Job et al. 2007).