Gabella G, Trigg P, McPhail H
Department of Anatomy, University College London, UK.
J Neurocytol. 1988 Dec;17(6):753-69. doi: 10.1007/BF01216704.
Neurons and glial cells of the superior cervical ganglion of sheep were investigated with morphometric methods in the light and electron microscope. The nerve cell sectional area (measured on nucleated cell profiles) ranged from 165 to 2500 microns2, which corresponds to range in cell diameter from 14 to 56 microns and a range in cell volume from 1600 to 93,000 microns3, i.e. a 60-fold volume difference between smallest and largest neurons. The distribution of cell sizes appeared unimodal, with a predominance of small neurons; there were no variations in different parts of the ganglion. This wide range in nerve cell sizes is discussed in the light of the suggestion that large neurons innervate a greater amount of target tissue (e.g. smooth muscle) and are less readily excitable than smaller neurons: it is thus possible that there is differential recruitment of ganglion neurons in autonomic reflexes. The ultrastructural features of ganglion neurons in the sheep were similar to those observed in small laboratory animals. The relative volumes of perikaryal cytoplasm occupied by mitochondria and Golgi apparatus were 8.5% and 4.8%, respectively, but the average values were the same in small and large neurons. Subsurface cisternae of endoplasmic reticulum were common in the perikaryon, while in the dendrites clusters of synaptic vesicles were found beneath the plasma membrane; the absence of a glial wrapping at the latter sites suggests that they are points of (non-synaptic) release of transmitters. The extent of the capsule that satellite cells form around each neurons was compared in size-based classes of neurons. There was no difference in the size of glial nuclei, and this suggests that glial cells are probably of uniform size. However, glial cells were more densely packed over the surface of large neurons than over the surface of small neurons--in fact the packing density was proportional to the ganglion neuron volume, rather than to its surface. The average thickness of the glial capsule was significantly greater around large than around small neurons. It is suggested that the matching of glial cell number and nerve cell volume is achieved during development by glial cell mitosis taking place long after the nerve cells have ceased dividing.
采用形态计量学方法，利用光学显微镜和电子显微镜对绵羊颈上神经节的神经元和神经胶质细胞进行了研究。神经细胞的横截面积（在有核细胞轮廓上测量）范围为165至2500平方微米，这对应于细胞直径范围为14至56微米，细胞体积范围为1600至93000立方微米，即最小和最大神经元之间的体积相差60倍。细胞大小的分布呈现单峰型，小神经元占优势；神经节不同部位无差异。根据大神经元支配更多靶组织（如平滑肌）且比小神经元更不易兴奋的观点，对神经细胞大小的这种广泛差异进行了讨论：因此，自主反射中神经节神经元可能存在差异性募集。绵羊神经节神经元的超微结构特征与在小型实验动物中观察到的相似。线粒体和高尔基体在核周细胞质中所占的相对体积分别为8.5%和4.8%，但大小神经元的平均值相同。内质网的表面池在核周很常见，而在树突中，在质膜下方发现了突触小泡簇；后者部位没有神经胶质包裹，这表明它们是递质（非突触性）释放的部位。在按大小分类的神经元中，比较了卫星细胞围绕每个神经元形成的被膜范围。神经胶质细胞核的大小没有差异，这表明神经胶质细胞可能大小均匀。然而，大神经元表面的神经胶质细胞比小神经元表面的更密集——实际上，堆积密度与神经节神经元体积成正比，而不是与其表面积成正比。大神经元周围神经胶质被膜的平均厚度明显大于小神经元周围的。有人提出，在发育过程中，神经胶质细胞有丝分裂发生在神经细胞停止分裂很久之后，从而实现神经胶质细胞数量与神经细胞体积的匹配。
