Walro J M, Kucera J
Am J Anat. 1985 May;173(1):55-68. doi: 10.1002/aja.1001730105.
Distributions of 53 motor axons to different types of intrafusal fibers were reconstructed from serial 1-micron-thick transverse sections of 13 poles of spindles in the rat soleus muscle. The mean number of motor axons that innervated a spindle pole was 4.1. Approximately 60% of motor axons lost their myelination prior to or shortly after entry into the periaxial fluid space of spindles. Motor innervation to the juxtaequatorial portion of nuclear bag fibers (particularly the bag1) consisted of groups of short, synaptic contacts that were terminations of thin, unmyelinated axons. In contrast, motor endings on both the bag1 and bag2 fibers were platelike in the polar intracapsular region. Chain fibers had a single midpolar platelike ending. The ratio of motor axons that innervated the bag1 fiber exclusively to axons that innervated bag2 and/or chain fibers was 1:1. However, one-fourth of motor axons coinnervated the dynamic bag1 fiber in conjunction with static bag2 and/or chain fibers. Thus the complete separation of motor control of the dynamic bag1 and static bag2 intrafusal systems observed in cat tenuissimus spindles is neither representative of the pattern of motor innervation in all other species of mammals nor essential to normal spindle function.
从大鼠比目鱼肌13个纺锤体极的连续1微米厚的横切片中重建了53条运动轴突到不同类型肌梭内纤维的分布。支配一个纺锤体极的运动轴突的平均数量为4.1。大约60%的运动轴突在进入纺锤体的轴周液空间之前或之后不久失去髓鞘。核袋纤维赤道旁部分（特别是袋1纤维）的运动神经支配由短的突触接触群组成，这些是细的无髓轴突的终末。相比之下，袋1和袋2纤维在极内囊区域的运动终末呈板状。链纤维有一个单极中部板状终末。仅支配袋1纤维的运动轴突与支配袋2和/或链纤维的轴突的比例为1:1。然而，四分之一的运动轴突与静态的袋2和/或链纤维共同支配动态的袋1纤维。因此，在猫的薄肌纺锤体中观察到的动态袋1和静态袋2肌梭内系统运动控制的完全分离，既不代表所有其他哺乳动物物种的运动神经支配模式，对正常纺锤体功能也不是必需的。
