Boskov D, Heckman C J
Northwestern University Medical School, Department of Physiology, Chicago, Illinois 60611, USA.
Biol Cybern. 1996 Sep;75(3):211-7. doi: 10.1007/s004220050288.
An important function of the stretch reflex in the soleus muscle in the decerebrate cat preparation is to compensate for the tendency of muscle suddenly to yield during ramp increases in length. As the level of background (i.e. pre-stretch) force increases, there is a systematic change in the curvature of the force trajectory during this reflex compensation, from concave to convex with respect to increasing force. The hypothesis that this change in curvature was due to background force-dependent changes in the recruitment pattern of motor units was investigated with a combined computer simulation/experimental technique. The simulation consisted of 20 model motor units for the soleus muscle, each based on a distributed moment muscle model. The timing of recruitment of the motor units was optimized to allow the simulation outputs to fit a set of experimental data records on the reflex response to stretch initiated at five different levels of pre-stretch force. The resulting recruitment patterns showed that a tendency for recruitment to be concentrated progressively in the early portion of the stretch as pre-stretch force increased could account for the changes in reflex force curvature. These results are consistent with the skewed distribution of intrinsic electrical thresholds of motoneurons, in which low-threshold units are much more frequent than high-threshold ones. Therefore the changes in recruitment pattern and reflex force curvature may be due primarily to the intrinsic properties of motoneurons.
在去大脑猫的实验准备中，比目鱼肌牵张反射的一个重要功能是补偿肌肉在长度呈斜坡式增加时突然屈服的倾向。随着背景（即预拉伸）力水平的增加，在这种反射补偿过程中，力轨迹的曲率会发生系统性变化，相对于增加的力而言，从凹形变为凸形。我们使用计算机模拟与实验相结合的技术，研究了这种曲率变化是由于运动单位募集模式中依赖于背景力的变化这一假设。模拟由20个比目鱼肌的模型运动单位组成，每个单位基于分布式力矩肌肉模型。对运动单位的募集时间进行了优化，以使模拟输出能够拟合在五个不同预拉伸力水平下开始的牵张反射反应的一组实验数据记录。由此产生的募集模式表明，随着预拉伸力的增加，募集逐渐集中在牵张早期部分的趋势可以解释反射力曲率的变化。这些结果与运动神经元固有电阈值的偏态分布一致，其中低阈值单位比高阈值单位更为常见。因此，募集模式和反射力曲率的变化可能主要归因于运动神经元的固有特性。
