Kucera J, Walro J M
Am J Anat. 1986 May;176(1):97-117. doi: 10.1002/aja.1001760108.
The form of terminations of fusimotor (gamma) and skeletofusimotor (beta) axons on intrafusal fibers was analyzed in serial sections of 20 spindles of the cat tenuissimus muscle. Seven synaptic features were assessed either qualitatively or quantitatively from electron micrographs of transverse sections of 184 intrafusal and 30 extrafusal endings. Features were compared among endings that were terminations of gamma or beta axons on different types of intrafusal fiber at different distances from the spindle equator. These comparisons indicated that interactions of several factors, and not the motor axon alone, determine the form of motor endings. Intrafusal muscle fiber type is dominant to the motor axon in regulation of the number and depth of postsynaptic folds. Separation of the influence of the motor axon from the muscle fiber was less clear with respect to the size of ending. Complete expression of the muscle fiber-motor axon interaction reflected by the form of motor endings is dependent upon location of the ending relative to the sensory region. Both depth of the primary synaptic cleft and size of the soleplate of motor endings increased with increasing distance of the ending from the spindle equator. A system of classification of cat intrafusal motor endings that reflects the multiplicity of factors that determine the form of endings, and one that simplifies the current terminology, is proposed.
在猫薄肌20个肌梭的连续切片中，分析了肌梭运动（γ）和骨胳肌梭运动（β）轴突在肌梭内纤维上的终末形式。从184个肌梭内终末和30个肌梭外终末的横切电子显微照片中，定性或定量地评估了七个突触特征。对γ或β轴突在距肌梭赤道不同距离处不同类型肌梭内纤维上的终末进行了特征比较。这些比较表明，是多种因素而非单一运动轴突相互作用决定了运动终末的形式。在调节突触后褶皱的数量和深度方面，肌梭内肌纤维类型比运动轴突更具主导性。就终末大小而言，运动轴突与肌纤维影响的区分不太明显。运动终末形式所反映的肌纤维 - 运动轴突相互作用的完全表达取决于终末相对于感觉区域的位置。随着终末距肌梭赤道距离的增加，初级突触裂隙的深度和运动终末终板的大小均增加。本文提出了一种猫肌梭内运动终末的分类系统，该系统反映了决定终末形式的多种因素，并且简化了当前的术语。
