Roy R R, Garfinkel A, Ounjian M, Payne J, Hirahara A, Hsu E, Edgerton V R
Brain Research Institute, University of California, Los Angeles 90095-1761, USA.
Muscle Nerve. 1995 Oct;18(10):1187-95. doi: 10.1002/mus.880181015.
The motor unit is the basic unit for force production in a muscle. However, the position and shape of the territory of a motor unit within the muscle have not been defined precisely. The territories of five motor units in the cat tibialis anterior muscle were reconstructed three-dimensionally (3-D) from tracings of the glycogen-depleted fibers belonging to each unit. The motor unit territories did not span the entire length of the muscle and their cross-sectional areas tapered along the proximodistal axis producing a conical shape. In addition, the position of the territory of each unit shifted in an anterior-posterior plane along the longitudinal axis of the muscle, presumably as a consequence of the pinnation of the fibers. The area of the motor unit territory at any given level along the proximodistal axis was highly correlated with the number of fibers within the territory at that level. Connective tissue boundaries (outlining fascicles) appeared to have a strong influence on the shape of the territory, territories showed abrupt changes at connective tissue boundaries as groups of motor unit fibers within a fascicle often terminated together while motor unit fibers in neighboring fascicles did not terminate. It is likely that the mechanical impact of the recruitment of a motor unit is affected by the location and shape of motor units within the same muscle area.(ABSTRACT TRUNCATED AT 250 WORDS)
运动单位是肌肉中产生力量的基本单位。然而，运动单位在肌肉内的分布区域的位置和形状尚未得到精确界定。通过对猫胫骨前肌中属于每个运动单位的糖原耗尽纤维进行追踪，三维重建了五个运动单位的分布区域。运动单位分布区域并未跨越肌肉的整个长度，其横截面积沿近端到远端的轴线逐渐变细，呈圆锥形。此外，每个运动单位分布区域的位置沿肌肉纵轴在前后平面内发生移动，推测这是纤维羽状排列的结果。沿近端到远端轴线的任何给定水平处，运动单位分布区域的面积与该水平处分布区域内的纤维数量高度相关。结缔组织边界（勾勒出肌束）似乎对分布区域的形状有很大影响，在结缔组织边界处分布区域会出现突然变化，因为一个肌束内的一组运动单位纤维通常一起终止，而相邻肌束中的运动单位纤维不会同时终止。同一肌肉区域内运动单位的位置和形状可能会影响运动单位募集的机械效应。（摘要截选至250字）
