Basic contraction properties of the avian stapedius muscle

Area of Science:

• Physiology
• Muscle Biology
• Bioacoustics

Background:

• The M. stapedius is the only middle ear muscle in birds.
• Previous studies on in situ preparations suggested both fast and slow components in its response.

Purpose of the Study:

• To investigate the basic contraction properties of the isolated avian M. stapedius muscle (Gallus gallus).
• To classify the M. stapedius as a fast or slow muscle based on its physiological responses.

Main Methods:

• Isolated M. stapedius muscle preparation from Gallus gallus.
• Measurement of muscle tension using a sensitive tension transducer.
• Electrical stimulation with single pulses and repetitive frequencies (2.5-200 Hz).

Main Results:

• Single electrical stimulus pulses elicited rapid twitch contractions (average tension 46 mN).
• Contraction time was 15 ms, half relaxation time was 15 ms, and total twitch time was 54 ms.
• Maximum tension summation occurred at 10-20 Hz, with peak tension at 160 Hz ranging from 150-200 mN. The slow component observed in previous in situ studies was absent.

Conclusions:

• The M. stapedius of Gallus gallus is definitively classified as a fast-twitch muscle.
• Its contraction time is faster than that of the M. stapedius in mammals like cats and rabbits.
• Findings align with morphological studies indicating fast-twitch characteristics.