Chanaud C M, Pratt C A, Loeb G E
Laboratory of Neural Control, National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
Exp Brain Res. 1991;85(2):257-70. doi: 10.1007/BF00229405.
The goal of this study was to analyze the architecture of the cat biceps femoris (BF), a multifunctional hamstring muscle, and to evaluate the relationships between muscle architecture, limb position, and muscle function during natural movement. The BF muscle consists of three neuromuscular compartments: anterior (BFa), middle (BFm) and posterior (BFp). Each compartment is innervated by a separate nerve branch. Nerve branch stimulation and 2-dimensional surface EMG recordings showed that individual compartment territories were discrete and non-overlapping with well-defined borders. Comparisons of the three compartments revealed consistent differences in architecture, relationship to the skeleton, and function. The BFa crossed only the hip joint and appears to function as a pure hip extensor. The BFm had equal lever arm lengths to the hip and knee joints, appears to function as a hip extensor, and may contribute to knee flexion or femoral rotation. The BFp had a greater lever arm to the knee, functions as a knee flexor, and may contribute to hip extension, femoral rotation or ankle extension. Measurements of individual fascicles from the three compartments revealed a surprising range of lengths, 3.3-12.0 cm. Microdissection of gold-stained tissue showed that fascicles from all compartments were comprised of interdigitated, short fibers (range: 0.6-5.0 cm; average 2.14 cm) arranged in-series in fascicles, running parallel to the origin-insertion axis of each muscle compartment. In regions of fiber interdigitation, the fiber endings were round and tapered (taper lengths: 1-11 mm) although flat, tapering endings like ribbons were occasionally found. As hip and knee joint angles were varied over physiological ranges corresponding to minimal to maximal muscle length, fascicles of the three compartments changed length disproportionately. Long BFa fascicles maximally lengthened 10-18%, consistent with in vivo length measures during treadmill locomotion. However, the long BFp fascicles lengthened 25-45%, and the relatively short fascicles near the BFm/BFp border maximally lengthened 45-53%. How do these unexpectedly large length changes affect sarcomere lengths? Using laser diffraction to measure sarcomeres, static fascicle and sarcomere lengths were compared in muscles that went into rigor mortis after fixing the hip and knee joint angles. Sarcomeres within the short BFm/BFp and long BFp fascicles consistently lengthened proportionately less than the whole fascicle. It remains to be determined how and where the fascicle length changes are dissipated in the connective tissue between the interdigitated muscle fibers and whether such a series-compliance operates during the large excursions over which this muscle normally works.
本研究的目的是分析多功能绳肌——猫股二头肌（BF）的结构，并评估自然运动过程中肌肉结构、肢体位置和肌肉功能之间的关系。BF肌肉由三个神经肌肉部分组成：前部（BFa）、中部（BFm）和后部（BFp）。每个部分由单独的神经分支支配。神经分支刺激和二维表面肌电图记录显示，各个部分的区域是离散的，边界清晰，互不重叠。对这三个部分的比较揭示了在结构、与骨骼的关系以及功能方面存在一致的差异。BFa仅跨过髋关节，似乎起到单纯的髋关节伸肌作用。BFm到髋关节和膝关节的力臂长度相等，似乎起到髋关节伸肌的作用，并且可能有助于膝关节屈曲或股骨旋转。BFp到膝关节的力臂更大，起到膝关节屈肌的作用，并且可能有助于髋关节伸展、股骨旋转或踝关节伸展。对来自这三个部分的单个肌束进行测量，发现其长度范围惊人，为3.3 - 12.0厘米。对金染组织进行显微解剖显示，所有部分的肌束均由相互交错的短纤维组成（长度范围：0.6 - 5.0厘米；平均2.14厘米），这些纤维在肌束中串联排列，平行于每个肌肉部分的起止轴。在纤维交错区域，纤维末端呈圆形且逐渐变细（渐细长度：1 - 11毫米），不过偶尔也会发现像丝带一样扁平、逐渐变细的末端。当髋关节和膝关节角度在对应于最小到最大肌肉长度的生理范围内变化时，这三个部分的肌束长度变化不成比例。BFa的长肌束最大伸长10 - 18%，这与跑步机运动期间的体内长度测量结果一致。然而，BFp的长肌束伸长25 - 45%，而BFm/BFp边界附近相对较短的肌束最大伸长45 - 53%。这些出乎意料的大长度变化如何影响肌节长度呢？通过激光衍射测量肌节，在固定髋关节和膝关节角度后进入尸僵状态的肌肉中比较了静态肌束和肌节长度。BFm/BFp短肌束和BFp长肌束内的肌节伸长比例始终小于整个肌束。肌束长度变化如何以及在何处消散于交错肌纤维之间的结缔组织中，以及在该肌肉正常工作的大幅度运动过程中这种串联顺应性是否起作用，仍有待确定。
