Motoneuronal pre-compensation for the low-pass filter characteristics of muscle. A quantitative appraisal in cat muscle units
Motoneuronal pre-compensation for the low-pass filter characteristics of muscle. A quantitative appraisal in cat muscle units
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DOI：
10.1111/j.1469-7793.1998.611bh.x
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发表时间：
1998-09-01
影响因子：
5.5
通讯作者：
Cerri, G
中科院分区：
文献类型：
--
作者：
Baldissera, F;Cavallari, P;Cerri, G
1.通过用两个电流-速率转换器产生的脉冲放电刺激猫肌肉单位(MU)来评估运动神经元动态敏感性在补偿肌肉低通滤波特性中的相关性：(I)脊髓运动神经元，对输入强度及其一阶导数敏感；(Ii)线性电流-速率转换器，即具有与运动神经元相同的静态敏感性但缺乏动态敏感性的神经元模型。在三个‘快速’类型的运动神经元中注入正弦波电流所产生的放电，在三个相关的模型版本中仅适用于46微米的轴突。以电流正弦波的频率(0.5~20赫兹)调制MU等长张力。测量了电流-力转换的相位和增益。当由该模型驱动MU时，在慢MU中，力滞后电流90°，在快MU中，在约5 Hz时，力滞后电流。在运动神经元驱动下，在大约两倍高的频率下，获得了90度的相位滞后。随着调制频率的增加，换能器(峰峰力调制/峰峰电流调制)的增益衰减。除5个单位外，所有单位的截止频率F-co(增益衰减-3分贝)，当单位是运动神经元驱动(F-co Cell)时高于模型驱动(F-co Mod)。在这两种情况下，F-co与MU的峰值时间呈负相关。运动神经元动态敏感性的优势通过F-co比率(F-co Cell/F-co Mod)来表示。在MU人群中，这一比率在0.6-2.8之间，与到达峰值的时间呈负相关，与半张力率直接相关，即MU产生最大强直力的50%的冲动率。最大的改善(F-CO比率>；2.0)被发现在机械特征类似于那些可能在体内连接到用于刺激的运动神经元的单元中。这一估计在实验中得到了证实，在实验中，通过在另一个运动神经元和相关模型中注入斜坡电流产生的脉冲序列来激活8个MU，这些MU被选为类似于在体内连接到运动神经元的MU。正如预期的那样，对于任何gis en Current斜率，当单元被运动神经元驱动时，等长张力的上升阶段比它们被模型驱动时更陡峭。将增益(力斜率/电流斜率)与斜率作图，以确定增益衰减-3分贝的截止斜率S-CO。在这个均匀的MU样本中，表示运动神经元驱动优势的比率(S-co细胞/S-co模式，相当于F-co比率)范围在2.62-2.97之间，与正弦波实验中观察到的当运动神经元和肌肉单位适当匹配时的值相当。
1. The relevance of motoneurone dynamic sensitivity in compensating for the low-pass filter properties of muscle was assessed by stimulating cat muscle units (MUs) with impulse discharges generated by two current-to-rate converters: (i) a spinal motoneurone, sensitive to both the input intensity and its first derivative, and (ii) a linear current-to-rate converter, i.e. a neurone model with the same static sensitivity as the motoneurone but lacking dynamic sensitivity.2. Discharges generated by injection of sine-wave currents in three motoneurones of the 'fast' type and in the three related model versions mere applied to the axon of forty-six MUs. The MU isometric tension was modulated at the frequency of the current sine wave (0.5-20 Hz). Phase and gain of the current-to-force transduction were measured.3. When MUs were driven by the model, the force lagged the current by 90 deg at 1 Hz in slow MUs and at around 5 Hz in fast MUs. Under motoneurone drive, the 90 deg phase lag was attained at frequencies about twice as high.4. The gain of the transduction (peak-to-peak force modulation/peak-to-peak current modulation) decayed when the modulation frequency was increased. In all but five units, the cut-off frequency, F-co (gain attenuated by -3 dB), was higher when the unit was motoneurone driven (F-co Cell) then when it was model driven (F-co Mod). In both conditions, F-co was inversely correlated with the MU's time-to-peak. The advantage conferred by the motoneurone dynamic sensitivity was expressed by the F-co ratio (F-co Cell/F-co Mod). Across the MU population this ratio ranged from 0.6-2.8, was inversely correlated with the time-to peak, and was directly correlated with the half-tension rate, i.e. the impulse rate at which MUs develop 50% of their maximal tetanic force. The largest improvement (F-co ratio > 2.0) was found in units with mechanical features similar to those presumably coupled 'in vivo' to the motoneurones utilized for stimulation.5. This estimate was confirmed in experiments in which trains of pulses, generated by injection of ramp currents in another motoneurone and the related model, were used to activate eight MUs, selected for being similar to that connected 'in vivo' to the motoneurone. As expected, for any gis en current slope the rising phase of isometric tension was steeper when units were motoneurone driven than when they were model driven. The gain (force slope/current slope) was plotted against the ramp slope to identify the cut-off slope, S-co, at which the gain was attenuated by -3 dB. In this homogeneous MU sample, the ratio expressing the advantage of the motoneurone drive (S-co Cell/S-co Mod, equivalent to the F-co ratio), ranged from 2.62-2.97, values comparable with those observed in sine-wave experiments when the motoneurone and muscle units were properly matched.