Sokoloff A J, Ryan J M, Valerie E, Wilson D S, Goslow G E
Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912.
Biology Department, Hobart and Williams Smith College, Geneva, New York 14456.
J Morphol. 1998 Jun;236(3):179-208. doi: 10.1002/(SICI)1097-4687(199806)236:3<179::AID-JMOR3>3.0.CO;2-Z.
We used acid digestion and glycogen depletion to determine fascicle organization, fiber morphology, and physiological and anatomical features of individual motor units of an in-series muscle, the pectoralis (pars thoracicus) of the pigeon (Columba livia). Most fascicles are attached at one end to connective tissue. Average fiber length in the four regions examined range from 42% to 66% of average fascicle length. More than 65% of fibers are blunt at one end of a fascicle and taper intrafascicularly. Fibers with blunt-blunt endings range from 13% to 31% of the population in different regions; taper-taper fibers range from 2% to 17%. Pigeon pectoralis fibers are distinguished histochemically into fast-twitch glycolytic (FG) and fast-twitch oxidative-glycolytic (FOG) populations. Three units composed of FG fibers (FG units) contract more quickly than three units composed of FOG fibers (FOG units) (range 31-37 vs 47-62 msec), produce more tetanic force (0.11-0.32 vs 0.02-0.05 N) and are more fatigable (<18% initial force vs >50% after repeated stimulation). Most motor units are confined to one of the four muscle regions. Territory of two FOG units is <30% of parent fascicle length. Territories of other units spanned parent fascicles; most fibers in these units do not extend the full fascicle length. Compared to FG units, FOG units have lower maximum innervation ratios and density indices (ratio of depleted/total FOG fibers in territory 8-14% vs 58-76% for FG units). These differences support the hypothesis that FG units are organized to produce substantial force and power for takeoff, landing and other ballistic movements whereas FOG units are suited for sustained flight when power requirements are reduced. Implications of findings for understanding the control of in-series muscles and the use of connective tissue elastic elements during wing movements are discussed. J.Morphol. 236:179-208, 1998. © 1998 Wiley-Liss, Inc.
我们采用酸消化法和糖原耗尽法来确定串联肌肉——家鸽（Columba livia）胸肌（胸段）单个运动单位的肌束组织、纤维形态以及生理和解剖学特征。大多数肌束一端附着于结缔组织。在所检查的四个区域中，平均纤维长度为平均肌束长度的42%至66%。超过65%的纤维在肌束一端呈钝形，并在肌束内逐渐变细。两端均为钝形的纤维在不同区域占总数的13%至31%；两端均逐渐变细的纤维占2%至17%。家鸽胸肌纤维在组织化学上可分为快缩糖酵解型（FG）和快缩氧化糖酵解型（FOG）两类。由FG纤维组成的三个运动单位（FG单位）比由FOG纤维组成三个运动单位（FOG单位）收缩更快（范围为31 - 37毫秒对47 - 62毫秒），产生的强直收缩力更大（0.11 - 0.32牛对0.02 - 0.05牛），且更易疲劳（重复刺激后初始力小于18%对大于50%）。大多数运动单位局限于四个肌肉区域之一。两个FOG单位的分布范围小于其母肌束长度的30%。其他单位的分布范围跨越母肌束；这些单位中的大多数纤维并未延伸至整个肌束长度。与FG单位相比，FOG单位的最大神经支配率和密度指数较低（分布区域内耗尽的/总的FOG纤维比例为8 - 14%，而FG单位为58 - 76%）。这些差异支持了这样的假说，即FG单位的组织方式是为起飞、着陆及其他爆发性运动产生强大的力量和功率，而FOG单位则适合在功率需求降低时进行持续飞行。本文还讨论了这些发现对于理解串联肌肉的控制以及翅膀运动过程中结缔组织弹性元件的作用的意义。《形态学杂志》236:179 - 208，1998年。© 1998威利 - 利斯公司。
