THE INFLUENCE OF A DOUBLET OF STIMULI AT THE BEGINNING OF THE TETANUSON ITS TIME-COURSE

The influence of a pair of stimuli generated in a short time sequence (doublet) at the beginning of stimulation on the time course of the fo llowing tetanus was investigated. Experiments were performed on single motor units in rat's medial gastrocnemius. The doublet evoked an incr ease in tetanic tension, tetanic fusion and the area under tension rec ord. These effects were measured in tetani fused to varying degrees. I t was found that for all types of motor units the strongest influence of the doublet was observed in half-fused tetani. Moreover, the double t influenced the first part of tetanus significantly more as compared to the second. Slow motor units showed greater sensitivity of the tens ion and the tetanus area to the doublet than fast units. The results s how that slow units are characterized by better summation of their ten sion at the beginning of a tetanus.