GROUP IA SYNAPTIC INPUT TO FAST AND SLOW TWITCH MOTOR UNITS OF CAT TRICEPS SURAE
GROUP IA SYNAPTIC INPUT TO FAST AND SLOW TWITCH MOTOR UNITS OF CAT TRICEPS SURAE
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DOI：
10.1113/jphysiol.1968.sp008526
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发表时间：
1968-01-01
影响因子：
5.5
通讯作者：
BURKE, RE
中科院分区：
文献类型：
--
作者：
BURKE, RE
应用细胞内记录技术，观察了Pen-Barbitone麻醉猫小腿三头肌运动神经元的Ia组突触传入特征。测定由细胞支配的肌肉单位的力学性质，并测量运动神经元的输入阻值。同名复合(电诱发)单突触兴奋性突触后电位(EPSP)的最大波幅与整个样本单位的运动神经元输入阻力值之间存在显著的正相关。在异名EPSP的情况下，同样的相关性也很显著，尽管有些不那么强烈。本文还研究了同名肌肉的小静态伸展所引起的起源于1a群的单位微型EPSP(MEPSP)的波幅分布。在所研究的运动神经元中，mEPSP分布的中值幅度与输入阻力值之间存在显著的正相关。在两个数据点都可获得的细胞中，mEPSP的中位数和最大同义复合EPSP的幅度之间也观察到正相关。在这些相关性中，来自腓肠肌和比目鱼肌运动池的相对高阻的S(慢抽动肌单位)运动神经元的突触电位幅度往往大于低阻的快抽动肌单位(F)的腓肠肌细胞。对不同运动神经元的同名单突触EPSP波形的观察表明，S细胞的持续时间明显长于F型细胞。这种差异不能完全由F型细胞和S细胞的平均时间常数值的相对较小差异所解释。在S运动神经元上，La组突触终末的密度往往高于F型细胞。此外，与接受相对较低输入密度的运动神经元的情况相比，接受相对高密度的1a组输入的细胞显然倾向于将这种输入分配到远端膜区域。
The characteristics of the group Ia synaptic input to triceps surae motoneurons were examined in pento-barbitone-anesthetized cats, using intracellular recording techniques. The mechanical properties of the muscle units innervated by the cells were determined and the motoneuron input resistance values were also measured. A significant positive correlation was found between the maximum amplitudes of homonymous composite (electrically evoked) monosynaptic excitatory post-synaptic potentials (EPSPs) and the motoneuron input resistance values across the entire population of units sampled. The same correlation in the case of heteronymous EPSPs was also significant although somewhat less strong. The distribution of the amplitudes of unitary miniature EPSPs (mEPSPs) of presumed group la origin, elicited by small static stretches of the homonymous muscles, were also studied. A significant positive correlation was found between the median amplitudes of the mEPSP distributions and the input resistance values in the motoneurons studied. Positive correlation was also observed between the amplitudes of the median mEPSPs and the maximum homonymous composite EPSPs in the cells for which both data points were available. In each of these correlations, the synaptic potential amplitudes tended to be larger in the relatively high resistance type S (slow twitch muscle unit) motoneurons from both gastrocnemius and soleus motor pools, than in the lower resistance type F (fast twitch muscle unit) gastrocnemius cells. Examination of the shape of the homonymous monosynaptic EPSP wave forms in different motoneurons showed that these tended to be significantly longer in duration in type S cells than in type F. This difference could not be entirely accounted for by the relatively small difference in mean time constant values found in types F and S cells. The density of group la synaptic terminals tends to be higher on type S motoneurons than on the type F cells. Further, cells receiving a relatively high density of group la input apparently tend to have a greater proportion of this input distributed to distal membrane regions than is the case in motoneurons receiving a relatively low input density.