Action of the Middle Ear Muscles in Normal Cats

TLDR

The study implanted permanent electrodes on the cochlear round window in cats to record auditory responses. The middle ear muscles neither alter absolute hearing sensitivity nor significantly influence sound transmission, but they contract within 15 ms of intense stimuli, attenuate tones between 500 and 3000 Hz, protect the ear from loud sounds, and spontaneous contractions intermittently reduce transmission, with the stapedius muscle playing a greater role than the tensor tympani.

Abstract

Wires have been permanently implanted on the round window of the cochlea in cats. The voltage output of ears responding to sound stimulation has thus been made continuously available in unanesthetized animals for periods up to 4 months. By cutting the middle ear muscles of one ear and comparing its responses with those derived from the normal ear on the opposite side, it has been shown that the muscles: (1) do not appreciably influence absolute sensitivity, (2) contract to intense stimuli within 15 msec of their delivery to either ear, (3) attenuate transmission of tones between at least 500 and 3000 cps, and (4) significantly protect the ear against damage from intense sounds. Spontaneous contractions sporadically and intermittently introduce a transmission attenuation of several decibels in the resting normal cat. The stapedius muscle is much more important than the tensor tympani in producing these effects.