Movements of the Eardrum Following Intra-Aural Muscle Reflexes

Abstract

In recent years there has been a revival of interest in the reflectory contractions of the tympanic muscles since the acoustic reflexes of these muscles were proved to be of diagnostic value in various diseases. Until the beginning of this century extensive research was devoted to the function of these muscles, mostly based on direct observations in animal experiments, using acoustic stimuli or irritation of the fifth and seventh cranial nerves. Summarizing this work it may be stated that musculus stapedius is innervated by the facial nerve and musculus tensor tympani by the trigeminus. During contractions the stapedius muscle pulls the drum outward, while the tensor muscle pulls it medially. Contractions of both muscles are elicited by sounds of a certain intensity via the cochlea and the acoustic pathways, the reflex arc not going above the brain stem. Contractions serve the purpose of protecting the cochlea against intense sound pressures.