Basic contraction properties of the avian stapedius muscle

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Abstract
The basic contraction properties of the solitary avian middle ear muscle, m. [musculus] stapedius, was investigated in chicken, G. gallus, by a sensitive tension transducer. In situ muscle preparation revealed both fast and slow components in the muscle''s physiological responses. Brief electrical stimulus pulses delivered to the isolated m. stapedius elicited rapid twitch contractions with average tension levels of 46 mN for maximal stimulation. The contraction time was 15 ms, the half relaxation time was 15 ms and the total twitch time was 54 ms. Repetitive stimulation (2.5-200 Hz) revealed minimal summation of responses at 10-20 Hz and apparent complete fusion at 160 Hz. Peak tension at 160 Hz ranged from 150-200 mN. The twitch tetanus ratio was 0.25. In earlier experiments with an in situ preparation, a slow component was observed in the physiological responses. This slow component was not seen in the single twitch responses or the response to repetitive stimulation. The m. stapedius of G. gallus was a fast muscle. Its contraction time is slightly shorter than the contraction times of the m. stapedius in mammals such as the cat (21 ms) and the rabbit (22 ms). The m. stapedius of G. gallus apparently has the features of a fast twitch muscle.