THE CONTROL OF HUMAN MOTOR UNITS

1. The motor unit, consisting of a single motor neuron and the skeletal muscle fibres that it innervates, is the final output pathway of the motor system. 2. Much is now known about the way that human motor neurons are recruited and controlled during voluntary and reflex movements. This review briefly summarizes some of the recent experimental data that has contributed to our present understanding. The review is largely limited to data obtained in human experiments. While much of what we know about the organization of the nervous system has come from studies of the anatomy and physiology of experimental animals, there are some questions that cannot be addressed in reduced animal preparations. The development of new techniques has made it possible to investigate the human nervous system at a level of detail that has not hitherto been possible.     

还原型谷胱甘肽和L-NAME对体外培养的脊髓运动神经元的影响

目的 :探讨还原型谷胱甘肽 (GSH)和L NAME对体外培养的脊髓运动神经元的保护作用。方法 :不同浓度的GSH和L NAME作用于脊髓运动神经元 ,3d后计算存活率。并测量存活率高的两组和对照组的免疫细胞化学标本的神经元形态学指标。结果 :GSH 10mmol·L-1和L NAME 1× 10 -3 mol·L-1组存活率最高。两实验组轴突长度、树突总长度、树突分叉点数目和胞体面积高于对照组。结论 :抗氧化剂和NOS抑制剂可以提高脊髓运动神经元的存活率 ,促进神经元生长     

5-羟色胺免疫阳性纤维和终末在大鼠舌下神经伸、缩舌肌运动神经元的分布

5-羟色胺（5－HT）参与舌和面口部精细运动的调节。5－HT对舌下神经运动神经元功能的调控表现为兴奋性作用。本文首先采用免疫组化方法，在光镜下观察了大鼠舌下神经核内5－HT免疫阳性纤维的形态和分布特征。又进一步采用荧光逆行追踪结合固定脑片细胞内LuciferYellow染色和荧光免疫组织化学染色，通过共聚焦激光扫描显微镜观察了伸舌肌（颏舌肌、颏舌骨肌）和缩舌肌（茎突舌肌）运动神经元与5－HT免疫阳性纤维及其终末的解剖学关系。结果证明：舌下神经核有较丰富的5－HT阳性纤维，以尾侧段的背侧部和吻侧段的腹侧部较为密集；根据纤维及其膨体的形态特征，本文将此阳性纤维分为三种类型。5－HT免疫阳性膨体样纤维及其终末与舌下运动神经元的胞体、树突分枝和轴丘及轴突起始段形成紧密接触；这些接触多呈不均匀的簇状（由2～7个紧密接触点组成）分布。定量分析发现：在额舌肌神经元和茎突舌肌神经元，除少量分布在胞体（密度为3．4～6．7／1000μm2）外，主要分布在近段和中段树突分权处附近；但是在颏舌骨肌神经元则集中分布在跑体（密度为10．8～17．6／1000μm2）和近侧树突上。以上所见提示：5－HT对舌下神经核整体行为的调节在不同功能的亚核可能有所选择；5－HT调制舌下运动神经元兴奋性的方式可     

Synaptic actions of the ventral root afferents on cat hindlimb motoneurons

Postsynaptic potentials (PSPs) with long latencies were evoked in cat hindlimb motoneurons by stimulation of the distal stump of a cut ventral root. Measurements of their latency and the threshold in the responsible afferent fibers showed that they were produced mainly by the activity of the unmyelinated fibers in the ventral root that enter the spinal cord through the dorsal root. Patterns of PSPs evoked in flexor and extensor motoneurons by ventral root stimulation were similar to those observed in the flexion reflex.     

Localization of motoneurons innervating the stylopharyngeus muscle in the cat

Recent investigations of the nucleus ambiguus (NA) have attempted to identify motoneurons associated with muscles of the larynx and pharynx. However, relatively little attention has been directed to the stylopharyngeus muscle, which is important in elevation of the pharynx in swallowing and speech. The present study was designed to identify the specific location of stylopharyngeus motoneurons within the brainstem. Horseradish peroxidase or fluorescent dye was injected into the stylopharyngeus muscle of 12 cats. Retrogradely labeled cells were located ipsilateral in the rostral NA and retrofacial nucleus. This is the first report to definitively localize stylopharyngeus motoneurons.     

大鼠三角肌前,后部的运动神经元

为了解主动肌与拮抗肌的运动神经元，应用ＨＲＰ逆行追踪技术研究了大鼠三角肌前部、后部的运动神经元。三角肌前部的运动神经元池位于Ｃ４－６脊髓前外侧核背部及其与后外侧核之间。三角肌后部的运动神经元池位于Ｃ４－７脊髓外侧核及其与前外侧核之间。与前池略有重叠。     

大鼠脊髓损伤后NGF及其受体TrkA在运动神经元及神经胶质细胞表达的变化

为探讨脊髓损伤后运动神经元及神经胶质细胞内神经生长因子(NGF)及其高亲和力受体(TrkA)表达的变化,用改良Allen重击法损伤SCI组动物T12脊髓,按伤后存活时间再将动物分为脊髓损1 d组、2 d组和5 d组。各组动物的脊髓切片经ABC法免疫组织化学染色,用光镜观察TrkA及NGF在脊髓前角运动神经元表达的变化和胶质纤维酸性蛋白(GFAP)及NGF免疫反应阳性胶质细胞的反应性增生程度,并进行图像分析。结果显示:脊髓损伤后前角运动神经元TrkA及NGF的表达随脊髓损伤后动物存活时间的延长逐渐上调;脊髓白质和灰质内尤其是皮质脊髓束内GFAP及NGF阳性胶质细胞明显增生;与此同时,室管膜细胞内亦可见明显的NGF免疫反应产物。上述结果表明,脊髓损伤可刺激脊髓前角运动神经元表达TrkA及NGF,通过自分泌维持受损神经元的存活;损伤部位反应性增生的胶质细胞亦可产生NGF,通过旁分泌作用于脊髓前角运动神经元或皮质脊髓束的轴突末梢,以维持运动神经元的存活及促进皮质脊髓束的再生;适时补充外源性神经营养素或改变损伤局部的微环境将有利于受损脊髓的修复和再生。     

Properties and localization of the anterior semicircular canal-activated vestibulocollic neurons in the cat

Summary Unit activites of secondary vestibular neurons that selectively responded to stimulation of the anterior semicircular canal nerve (ACN) were recorded extracellularly in the anesthetized cat. Axonal pathways and projections in the spinal cord of the ACN-activated neurons were examined by recording their antidromic responses to stimulation of the lateral and medial vestibulospinal tracts (LVST and MVST), and the bilateral neck extensor motoneuron pools in the C₁segment (C₁dorsal rami [DR] motoneuron pools). In order to determine whether the neurons had ascending axon collaterals to the extraocular motoneurons, the contralateral (c-) inferior oblique (IO) motoneuron pool was also stimulated. Twenty-seven neurons sent their axons to the ipsilateral (i-) C₁DR motoneuron pool via the LVST without any projection to the extraocular motoneuron pool. All the cells except one were located in the ventral part of the lateral vestibular nucleus. This pathway produced monosynaptic EPSPs with short time-to-peak and short half-width in C₁DR motoneurons (16/16 motoneurons). Eight neurons sent axons to the i-C₁DR motoneuron pool via the MVST without any to the extraocular motoneuron pool. Cell somata were located in the descending nucleus or in the ventral part of the lateral nucleus. These neurons did not produce postsynaptic potentials (PSPs) in any C₁DR motoneurons. All thirty-five neurons sending axons to the c-C₁DR motoneuron pool have ascending axon collaterals to the c-IO motoneuron pool.     

外周神经损伤后对大鼠脊髓运动神经元及背根节感觉神经元的影响

大鼠左腓总神经离断后与胫神经端侧吻合,于术后第1至8周取L4～5脊髓和背根节（DRG）做冰冻切片,分别显示前角运动神经元（SMN）AChE活性和DRG神经元NOS活性。结果发现;①正常鼠SMN－AChE活性中－强度阳性反应。实验组外侧核SMN－AChE活性和阳性细胞数,于术后2～3周比正常者明显减低,有的SMN－核周体出现空泡样变性;术后4～8周,SMN酶活性和阳性细胞数渐增,并明显高于正常者。同体对照组与实验组同期比较,SMN酶活性相对较弱。②正常鼠部分中－小型DRG神经元NOS活性为中－强度阳性反应。实验组于术后第1～4周,NOS活性和阳性细胞数较正常者明显增高;术后第5～8周其渐趋正常。对照组DRG神经元NOS活性表达较强及与实验组有相应的变化梯度。二组DRG内均见到空泡样变性的神经元核周体。结果提示,坐骨神经慢性损伤所产生SMN－AChE活性增强,可能是轴突再生的反应,并对由NO介导的一级感觉信息传导有一定影响。     

The Extent of the Dendritic Tree and the Number of Synapses in the Frog Motoneuron

Frog motoneurons were intracellularly labelled with cobaltic lysine in the brachial and the lumbar segments of the spinal cord, and the material was processed for light microscopy in serial sections. With the aid of the neuron reconstruction system NEUTRACE, the dendritic tree of neurons was reconstructed and the length and surface area of dendrites measured. The surface of somata was determined with the prolate - oblate average ellipsoid calculation. Corrections were made for shrinkage and for optical distortion. The mean surface area of somata was 6710 microm2; lumbar motoneurons were slightly larger than brachial motoneurons. The mean length of the combined dendritic tree of brachial neurons was 29 408 microm and that of lumbar neurons 46 806 microm. The mean surface area was 127 335 microm2 in brachial neurons, and 168 063 microm2 in lumbar neurons. The soma - dendrite surface area ratio was 3 - 5% in most cases. Dendrites with a diameter of motoneuron dendrites (Antal et al., J. Neurocytol., 15, 303 - 310, 1986; 21, 34 - 49, 1992), and from the present data, the number of synapses on the dendritic tree was calculated. The calculations indicated 26 949 synapses on the smallest and 61 519 synapses on the largest neuron if the synaptic density was multiplied by the length of the dendritic tree. If the synaptic density was multiplied by the surface area of the dendritic tree the calculation yielded 23 337 synapses for the smallest and 60 682 synapses for the largest neuron. More than 60% of the combined surface area of dendrites was >600 microm from the soma. This suggests that about two-thirds of the synapses impinged upon distant dendrites >600 microm from the soma. The efficacy of synapses at these large distances is investigated on model neurons in the accompanying paper (Wolf et al., Eur. J. Neurosci., 4 1013 - 1021, 1992).