Research on the double innervation of trapezius muscle and the mechanisim of the axons extension direction

颈神经腹支和脊副神经（SAN）之间的交通分支也发送运动纤维供给斜方肌。然而，交通支的运动纤维类型及其周围分布，以及运动神经元的定位仍不清楚，这些运动神经元直接通过SAN或通过颈神经腹支延伸轴突支配斜方肌。采用顺行示踪法测定肌肉运动纤维的交通支内纤维成分及其周围分布。此外，运动神经元的定位也通过荧光染料标记和3D重建方法进行了研究，这些运动神经元通过轴突直接通过SAN或通过颈神经腹支支配肌肉。结果表明，在肌外纤维上观察到少量来自交通支的运动端板，而在肌内纤维中，更多的来自交通支的运动元件分布在束内纤维的极性部分。结果表明，通过交通支供给斜方肌的运动纤维以y运动纤维为主，也有少量a运动纤维。此外，在锁骨斜方肌、肩方肌和棘方肌吻侧均可见到交通支的a和γ运动纤维。另一方面，轴突穿过颈神经腹支进入SAN的运动神经元和直接通过SAN延伸轴突的运动神经元分布在前角的同一区域内。通过SAN延伸轴突的神经元比那些通过颈神经到达斜方肌的轴突直径大。此外，最终延伸到SAN的轴突从脊髓背外侧退出，而那些通过颈神经的轴突则从脊髓腹侧根伸出。我们认为延伸轴突通过SAN的神经元主要是α-运动神经元，而通过颈神经向斜方肌投射轴突的神经元主要是γ-运动神经元，因为外周部分的分布和纤维类型与中枢部分一致。综上所述，这些结果可以解释为什么使用SAN治疗臂丛损伤的患者保留了对斜方肌的一些控制

The communicating branch between the ventral rami of cervical nerves and the spinal accessory nerve (SAN) has been reported to also send motor fibers to supply the trapezius. However, the motor fiber type of the communicating branch and its peripheral distribution, and the localization of motoneurons, which extend axons either directly through the SAN or through the ventral rami of cervical nerves to innervate the trapezius are still unclear. To determine the fiber elements within the communicating branch and its peripheral distribution of the motor fibers in the muscle the anterograde tracing method was used. Moreover, the localization of motoneurons, which extend axons either directly through the SAN or through the ventral rami of cervical nerves to innervate the muscle are also investigated using fluorescent dye labeling and 3D reconstruction method.The results show that a few a motor end plates from the communicating branch were observed on the extrafusal fibers, while in the muscl … More e spindle the motor elements from the communicating branch were distributed to the polar portions of the intrafusal fibers. The results indicated that the motor fibers passing through the communicating branch to supply the trapezius are mainly y motor fibers, with some a motor fibers. Moreover, the a and γ motor fibers from the communicating branch were observed in the clavotrapezius, acromiotrapezius and the rostral part of spinotrapezius. On the other hand, the motoneurons whose axons pass through the ventral rami of cervical nerves and then enter the SAN, and those extending axons directly through the SAN are distributed within the same area in anterior horn. The neurons that extend axons through the SAN had a greater diameter than those axons that pass through the cervical nerves en route to the trapezius muscle. In addition, the axons that ultimately extend through the SAN exit the spinal cord dorsolaterally, while those that pass through the cervical nerves extend out the spinal cord through the ventral roots. We consider that the neurons that extend axons through the SAN are mainly α-motoneurons and that those projecting axons through the cervical nerves to the trapezius are mainly γ-motoneurons, because the distribution and fiber types of peripheral part are agreement with the central part. Taken together, these results could explain why patients in whom the SAN was used to treat brachial plexus injury retain some control of the trapezius muscle Less