Two groups of Golgi tendon organs in cat tibial anterior muscle identifiedfrom the discharge frequency recorded under a ramp-and-hold stretch

Twenty Golgi tendon organs (GTOs) from the tibial anterior muscle of the ca t were investigated under a ramp-and-hold stretch of the passive muscle. Th e stretch rare was varied between 1 and 100 mm/s, the stretch amplitude bet ween 0.1 and 7 mm, the prestretch of the muscle between 0 and 12 mm. The ac tion potential sequences of the GTOs were recorded, and discharge patterns derived from them. The basic discharge frequencies, namely the initial freq uency, the peak dynamic discharge, the maximum static value, and the final static value, were read from each discharge pattern. The tension of the mus cle was determined at the same points in time at which one of the basic dis charge frequencies was read from a discharge pattern. The static and dynami c properties of the GTOs were determined from the basic discharge frequenci es. Two groups of GTOs were identified. Four GTOs discharged with an initia l frequency and at the same time had static properties of small magnitude. Sixteen GTOs showed no initial activity and had static properties of large magnitude. The two groups of GTOs did not differ in their dynamic propertie s. The number of a-fibers activating a single GTO was determined from a fur ther 11 GTOs. Eight GTOs without initial activity were activated by a mean number of 9.7 alpha-fibers. Three GTOs discharging with initial activity we re activated by a mean number of 15.3 alpha-fibers. The two mean values wer e significantly different (p = 0.02). The identification of two groups of G TOs is explained by the GTOs being positioned differently within the muscle and its tendon. (C) 1999 Published by Elsevier Science B.V. All rights res erved.