Kudina L P
Institute for Problems of Information Transmission, U.S.S.R. Academy of Sciences, Moscow.
Electroencephalogr Clin Neurophysiol. 1988 Jun;69(6):576-80. doi: 10.1016/0013-4694(88)90170-8.
The excitability of a firing human motoneurone was tested by Ia afferent excitatory volleys. An H reflex was evoked by stimulation of the tibial nerve while the subjects maintained the background rhythmic firing of single MU of the soleus and of the medialis gastrocnemius during weak voluntary contraction. The mean background firing rate of MUs ranged from 3.6 to 9.4 imp/sec. In order to estimate the 'effectiveness' of an afferent volley, PSTHs were constructed. The firing index was used as a measure of motoneurone excitability. It has been shown that the 'effectiveness' of an afferent volley decreases with an increase in background firing rate of a MU. Such a dependence was deduced from changes in current motoneurone excitability within an interspike interval. The results indicate that during natural muscle contraction at a low firing rate of a motoneurone, the discharge rate is one of the factors affecting the excitability of a firing motoneurone and, hence, its input-output relations. The method of testing changes in human motoneurone excitability within an interspike interval may prove useful in studies on interaction of volleys arriving at a motoneurone via different excitatory inputs.
通过Ia传入兴奋性冲动来测试正在放电的人体运动神经元的兴奋性。在受试者进行弱自主收缩期间，刺激胫神经诱发H反射，同时保持比目鱼肌和腓肠肌内侧单个运动单位（MU）的背景节律性放电。运动单位的平均背景放电频率在3.6至9.4次/秒之间。为了估计传入冲动的“有效性”，构建了脉冲密度直方图（PSTHs）。放电指数用作运动神经元兴奋性的度量。已经表明，传入冲动的“有效性”随着运动单位背景放电频率的增加而降低。这种依赖性是从峰间期内当前运动神经元兴奋性的变化推导出来的。结果表明，在运动神经元低放电频率的自然肌肉收缩过程中，放电频率是影响正在放电的运动神经元兴奋性的因素之一，因此也是影响其输入-输出关系的因素之一。测试峰间期内人体运动神经元兴奋性变化的方法可能在研究通过不同兴奋性输入到达运动神经元的冲动相互作用方面有用。
