Synaptic strength as a function of motor unit size in the normal frog sartorius.

摘要: A wide range of motor unit sizes exists in each frog sartorius, with values tetanus and twitch tensions extending over 62- 400-fold ranges, respectively. These differences primarily represent the number, rather than size, muscle fibres unit. Tetanus-to-twitch tension ratios varied markedly between different units, ranging from 1.5 to 190. Because directly stimulated have tetanus/twitch no larger 3, it is concluded that high arise recruitment during which respond only subthreshold depolarization a twitch. Small as judged either by their or tension, were associated higher ratios, suggesting average safety margin increases unit's size. Indeed, when ratio used determine fraction neuromuscular junctions, observed there direct linear relationship size its over-all efficacy synaptic transmission. Measurements effects changes calcium concentration on confirmed last conclusion. Furthermore, this analysis revealed large although having transmission margins, are largely comprised junctions uniformly margin. In units smaller strengths become more evenly distributed values. had consistently longer rise-times did units. This decrease rise-time paralleled raising questions about regulation fibre contraction kinetics.