THE DYNAMIC-RESPONSE OF GOLGI TENDON ORGANS TO TETANIC CONTRACTION OFIN-SERIES MOTOR UNITS

Golgi tendon organs (TOs) display a dynamic response related to the ra te of tension development by the motor units (MUs) which activate each TO. When several MUs are activated together the response increases no n-linearly with respect to tension. The dynamic response has been re-e xamined by recording the responses of TOs, in the adult cat, to tetani c, isometric contractions of one or more MUs and has been found to com prise two components: for each MU-TO pair the instantaneous frequency between the first two impulses of the response was linearly related to the rate of rise of the tension, the slope of the relationship being greatest for the slow units. Similarly, when activating MUs were stimu lated together, the relationships between frequency and the initial ra te of tension rise were linear. When the relationships were expressed in terms of relative tension rate the organs were found to be most str ongly activated by the IIb muscle fibres, the responsiveness at the le vel of the whole muscle being reduced by unloading effects. The later component of the response showed an exponential relationship between d ischarge frequency and rate of tension development, the slope of the r elationship between frequency and the logarithm of tension rate being independent of MU size. Although absolute tension increases during a c ontraction, this did not appear to impinge on the response which was d ominated by the dynamic parameters of the contraction.