Tetanic response of the cricothyroid muscle.

Tetanic response of canine cricothyroid muscle tissue was investigated through a series of experiments conducted in vitro. Two separate portions of the cricothyroid muscle, namely the pars recta and pars oblique, were studied. Samples of the muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees +/- 1 degrees C and a pH of 7.4 +/- 0.05. Tetanic contraction of the muscle samples was obtained by field stimulation to the muscle through a pair of parallel-plate platinum electrodes and with a train of square pulses of 0.1-millisecond duration and 85-V amplitude. Isometric force responses of the pars recta and pars oblique muscles were obtained electronically with a dual servo system (ergometer). The effect of tissue elongation on the active and passive responses was quantified by stimulation of the sample during cyclic elongation. Both active and passive responses as a function of elongation were obtained on the same sample.