Ritz L A, Bailey S M, Carter R L, Sparkes M L, Masson R L, Rhoton E L
Department of Neuroscience, University of Florida College of Medicine, Gainesville 32610.
J Comp Neurol. 1991 Feb 8;304(2):316-29. doi: 10.1002/cne.903040212.
The terminal fields of primary afferent fibers from tail muscle spindle primary endings were mapped within cat sacrocaudal spinal cord (S3-Ca7), using intra-axonal recording and horseradish peroxidase staining techniques. We sought to determine the ipsilateral and contralateral projection patterns and to relate these to the fibers' muscles of origin. Fifty-three group Ia fibers were successfully stained. Segmental collaterals originated from either the ascending or descending branch within the dorsal columns. Collaterals coursed rostromedially within the dorsal columns and traversed the medial aspect of the dorsal horn. Ipsilateral terminations were similar for all fibers. Within the ventral horn, boutons were consistently observed in the medial or central portions of lamina VII. In lamina VIII, a variable number of boutons was seen on fine branches emerging from larger fibers coursing ventrally. Clusters of terminals were plentiful in the regions of motoneurons, i.e., lamina IX and the nucleus commissuralis. Terminals were found in the adjacent white matter. In addition to ipsilateral terminations, some group Ia fibers (20 of 53) had collateral branches that crossed ventrally to the central canal, terminating within the midline ventral gray commissure and/or the contralateral ventral horn. Crossed projections always originated in medial (dorsal or ventral), but not lateral, muscles of the tail. These data suggest that ipsilateral projections of group Ia fibers make connections on sacrocaudal motoneurons, on neurons mediating segmental reflex functions and on neurons conveying ascending information. It is speculated that crossed and uncrossed connections between group Ia fibers from medial muscles and bilateral dendritic trees of motoneurons subserve synchronized co-contraction of synergistic muscles located on the two sides of the body, such as with dorsal or ventral flexion of the tail. Group Ia projections from lateral muscles, that are entirely ipsilateral, would be involved with lateral movements of the tail.
运用轴突内记录和辣根过氧化物酶染色技术，在猫的骶尾脊髓（S3 - Ca7）内绘制了来自尾部肌肉梭初级末梢的初级传入纤维的终末区域图。我们试图确定同侧和对侧的投射模式，并将这些与纤维的起源肌肉联系起来。成功染色了53条Ia类纤维。节段性侧支起源于背柱内的升支或降支。侧支在背柱内沿吻内侧走行，并穿过背角的内侧。所有纤维的同侧终末相似。在腹角内，始终能在VII层的内侧或中央部分观察到终扣。在VIII层，在从腹侧走行的较大纤维发出的细支上可见数量不等的终扣。在运动神经元区域，即IX层和联合核内，终末簇丰富。在相邻的白质中也发现了终末。除了同侧终末外，一些Ia类纤维（53条中有20条）有侧支，这些侧支向腹侧越过中央管，终止于中线腹侧灰质连合和/或对侧腹角内。交叉投射总是起源于尾部的内侧（背侧或腹侧）肌肉，而非外侧肌肉。这些数据表明，Ia类纤维的同侧投射与骶尾运动神经元、介导节段性反射功能的神经元以及传递上行信息的神经元建立了联系。据推测，来自内侧肌肉的Ia类纤维与运动神经元的双侧树突之间的交叉和不交叉连接有助于身体两侧协同肌肉的同步共同收缩，例如尾部的背屈或腹屈。来自外侧肌肉的完全同侧的Ia类投射将参与尾部的侧向运动。
