Rodgers J F, Durbaba R, Taylor A, Fowle A J
Sherrington School of Physiology, UMDS, St. Thomas's Hospital Campus, London.
Exp Physiol. 1994 May;79(3):337-55. doi: 10.1113/expphysiol.1994.sp003769.
Comparisons were made between the results of testing muscle spindle primary afferents with low-frequency, large-amplitude sine waves of muscle stretch and with repeating ramp-and-hold stretches. Three different situations were explored, namely, activation with succinylcholine (SCh), generation of various fusimotor outflow patterns by brainstem stimulation and fusimotor activation by stimulation of single ventral root gamma-axons. With ramp-and-hold stretches the effects of bag1 fibre contraction were thought to be generally better represented by increases in the dynamic response to stretch (delta DD) than by increases in dynamic index. The equivalent effect on the sine wave response was an increase in the magnitude of the fitted sine (delta Mag). Static effects were best measured by increases in the initial frequency for ramps (delta IF) and by increases in the fitted centre frequency (delta CF) for sines. There was good agreement between sine and ramp testing in the case of SCh effects, but much less consistency during brainstem stimulation. Sine wave testing can be regarded as less efficient than ramp testing in distinguishing between static and dynamic actions because dynamic fusimotor stimulation causes equal rises in CF and Mag, but fourfold larger rises in DD than in IF. Ramp responses with combined dynamic and static fusimotor stimulation showed increases of both IF and DD as expected, but whilst sine wave responses always showed increase in CF, they often showed no increase in Mag. Comparisons of the effects of SCh, central stimulation and fusimotor stimulation showed that it is important to recognize the different effects of chain and bag2 intrafusal fibre activation as components of static fusimotor excitation. Stimulation of driving static axons (chain activation) raised the IF and CF often with 1:1 or 1:2 driving during the shortened phase of ramps and sines. However, the stretch response in both cases was either unchanged or reduced. Stimulation of a non-driving static fusimotor axon (bag2 activation) caused a marked rise in CF for sine waves and a fall in Mag, but a modest increase in ramp stretch sensitivity (DD) with no increase in dynamic index. A way is described for measuring flattening of sine wave responses as a possible way of detecting chain fibre activation. The consequences of these findings are discussed in relation to previous reports of the use of sine wave testing for assessing fusimotor mechanisms.
对使用低频、大幅度肌肉拉伸正弦波以及重复斜坡-保持拉伸来测试肌梭初级传入纤维的结果进行了比较。研究了三种不同情况，即使用琥珀酰胆碱（SCh）激活、通过脑干刺激产生各种梭内肌传出模式以及通过刺激单根腹侧根γ轴突进行梭内肌激活。对于斜坡-保持拉伸，与动态指数的增加相比，袋1纤维收缩的影响通常通过拉伸动态反应（δDD）的增加能得到更好的体现。对正弦波反应的等效影响是拟合正弦幅度（δMag）的增加。静态效应最好通过斜坡初始频率（δIF）的增加以及正弦拟合中心频率（δCF）的增加来衡量。在SCh效应的情况下，正弦测试和斜坡测试结果吻合良好，但在脑干刺激期间一致性较差。在区分静态和动态作用方面，正弦波测试可被视为比斜坡测试效率更低，因为动态梭内肌刺激会使CF和Mag等量增加，但DD的增加幅度是IF的四倍。动态和静态梭内肌刺激相结合时的斜坡反应显示IF和DD如预期那样都增加了，但虽然正弦波反应总是显示CF增加，但它们通常显示Mag没有增加。对SCh、中枢刺激和梭内肌刺激效果的比较表明，认识到链纤维和袋2梭内肌纤维激活作为静态梭内肌兴奋成分的不同效果很重要。刺激驱动静态轴突（链激活）在斜坡和正弦波的缩短阶段通常以1:1或1:2的驱动比例提高IF和CF。然而，两种情况下的拉伸反应要么不变要么降低。刺激非驱动静态梭内肌轴突（袋2激活）会导致正弦波的CF显著升高且Mag降低，但斜坡拉伸敏感性（DD）适度增加且动态指数无增加。描述了一种测量正弦波反应平坦化的方法，作为检测链纤维激活的一种可能方式。结合之前关于使用正弦波测试评估梭内肌机制的报告，对这些发现的结果进行了讨论。
