Stein Paul S G
Department of Biology, Washington University, St. Louis, MO 63130, USA.
Brain Res Rev. 2008 Jan;57(1):118-24. doi: 10.1016/j.brainresrev.2007.07.008. Epub 2007 Jul 31.
The turtle spinal cord contains a central pattern generator (CPG) that produces rhythmic hindlimb motor patterns during a rostral scratch. This review describes evidence in support of the hypothesis that the turtle rostral scratch CPG has a modular structure similar to that described in the Unit-Burst-Generator hypothesis for cat locomotion by Grillner. During normal rostral scratch in turtle, activity bursts rhythmically alternate with quiescence for each motor neuron pool; agonist activity rhythmically alternates with antagonist activity at each degree of freedom, e.g., hip, knee; and a transition from knee flexor to knee extensor motor neuron activity occurs midway during each hip flexor motor neuron burst. Hip extensor deletions, knee flexor deletions, and knee extensor deletions are motor pattern variations of rostral scratch. During each of these variations, agonist activity is rhythmic; antagonist activity and agonist quiescence are absent. Several classes of evidence during both normal and variation motor patterns support a modular organization of the turtle rostral scratch CPG: electroneurographic recordings from axons of motor neurons, intracellular recordings of synaptic potentials in motor neurons, and extracellular unit recordings from spinal interneurons. These data support the hypotheses that the knee extensor module is different from the hip extensor module and that the knee flexor module is different from the hip flexor module. Potential mechanisms for rhythmogenesis include reciprocal connections between agonist and antagonist modules at each degree of freedom, and agonist module rhythmogenesis. Additional tests of the modular hypothesis for turtle rostral scratch include unit recordings from knee-related interneurons during normal rostral scratch, as well as during knee-related deletions.
龟的脊髓包含一个中枢模式发生器（CPG），在向前抓挠时会产生有节奏的后肢运动模式。这篇综述描述了支持以下假设的证据：龟的向前抓挠CPG具有模块化结构，类似于格里尔纳提出的关于猫运动的单位爆发发生器假设中所描述的结构。在龟正常向前抓挠过程中，每个运动神经元池的活动爆发有节奏地与静止交替；在每个自由度（如髋、膝）上，主动肌活动有节奏地与拮抗肌活动交替；在每个髋屈肌运动神经元爆发的中途，会出现从膝屈肌运动神经元活动到膝伸肌运动神经元活动的转变。髋伸肌缺失、膝屈肌缺失和膝伸肌缺失是向前抓挠的运动模式变体。在这些变体中的每一种过程中，主动肌活动是有节奏的；拮抗肌活动和主动肌静止不存在。在正常和变体运动模式期间的几类证据支持龟向前抓挠CPG的模块化组织：运动神经元轴突的神经电图记录、运动神经元中突触电位的细胞内记录以及脊髓中间神经元的细胞外单位记录。这些数据支持以下假设：膝伸肌模块与髋伸肌模块不同，膝屈肌模块与髋屈肌模块不同。节律产生的潜在机制包括每个自由度上主动肌和拮抗肌模块之间的相互连接，以及主动肌模块的节律产生。对龟向前抓挠模块化假设的其他测试包括在正常向前抓挠期间以及与膝相关的缺失期间，对与膝相关的中间神经元进行单位记录。
