THE STRUCTURAL RELATIONS BETWEEN NERVE-FIBERS AND MUSCLE-CELLS IN THE URINARY-BLADDER OF THE RAT
THE STRUCTURAL RELATIONS BETWEEN NERVE-FIBERS AND MUSCLE-CELLS IN THE URINARY-BLADDER OF THE RAT
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DOI：
10.1007/bf01181533
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发表时间：
1995-03-01
期刊：
影响因子：
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通讯作者：
GABELLA, G
中科院分区：
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作者：
GABELLA, G
用连续切片方法对成年雌性大鼠膀胱肌内神经纤维进行了观察。观察到了以下几点。(1)神经束进入肌层后反复分支，几乎全部变成单一纤维，轴突变得静脉曲张，雪旺细胞鞘变薄、不完整或不存在，轴索与肌细胞膜之间的距离缩小到几十纳米。(2)所有单个轴突和一些束内轴突均为静脉曲张，但静脉曲张的特征是以度表示的，而不是全有或全无状态。(3)精索静脉曲张包括小泡(多为无颗粒型)、微管(与轴膜或小泡联系较少)、部分神经丝(在发育最好的精索中少见或不存在)、线粒体(平均大小小于核周)和少量内质网。(4)终末静脉曲张是轴突的真实解剖末端，常无雪旺细胞鞘，充满小泡，极少含有微管或神经细丝，靠近肌细胞：间隙常缩小至约10 nm。(5)雪旺细胞伴随着肌束内的轴突。与轴突轮廓的面积不同，神经胶质鞘的面积沿着神经纤维的长度变化很小，除了朝向神经纤维的末端。(6)精索静脉曲张周围的雪旺细胞鞘通常是不完整的；由此暴露的轴膜区域被基板覆盖，在这里被称为“窗口”。虽然一些曲张的窗口只有几十纳米宽，但另一些曲张有多个窗口，有些完全没有雪旺细胞，因此它们的整个轴膜与基底板接触。雪旺细胞从来不会延伸到轴突之外，而轴突常常(也可能总是)延伸到雪旺细胞之外。(7)精索静脉曲张节段的长度和直径各不相同，最窄的伴有较清晰的静脉曲张。有些静脉曲张节段直径小至50 nm，含有单个微管，缺少雪旺细胞鞘。另一些被雪旺细胞包裹的神经纤维只含有一根神经丝，或者根本没有细胞器。(8)轴突和肌肉细胞之间的特殊接触(神经-肌肉连接)很多，有四个特征：轴突是充满小泡的静脉曲张；轴膜外露(有窗口)；两膜之间的距离在10-100 nm之间，大多是30-50 nm；细胞间隙不包括纤维，如胶原，但被单一的基膜占据。然而，这些参数中的任何一个也可以发生“非耦合”(静脉曲张节段上的窗口；没有窗口的静脉曲张；远离肌细胞的外露轴膜)。(9)轴突间无直接接触。即使当它们在一束中彼此靠近时，它们总是被雪旺细胞过程分开。(10)肌细胞膜在静脉曲张下呈凹形；然而，神经-肌肉连接区的肌细胞超微结构特征与细胞其他区域的肌细胞并无不同。(11)平均每个肌肉细胞有一个以上的神经-肌肉连接部，并通过连续切片获得来自一个或两个轴突的多个神经末梢的肌细胞。(12)膀胱神经支配的一个显著特征是其超微结构参数的变异性。膀胱的神经支配似乎不是建立在一个严格的结构计划上，并提出了“松散模式的神经支配”的概念。
Intramuscular nerve fibres in the bladder of adult female rats were investigated by means of serial sections. The following observations were made. (1) Upon penetrating into the musculature the nerve bundles branch repeatedly, and almost all turn into single fibres; their axons become varicose, the Schwann cell sheath is attenuated, incomplete or absent, and the separation between axonal membrane and muscle cell membrane is reduced to tens of nanometres. (2) All single axons, and some of those within bundles, are varicose, but the characteristic of being varicose is expressed by degrees, and is not an all-or-none state. (3) Varicosities contain vesicles (mostly of the agranular type), microtubules (with little connection with the axolemma or the vesicles), some neurofilaments (scarce or absent in the best developed varicosities), mitochondria (whose size is on average smaller than those of the perikaryon, and a minute amount of endoplasmic reticulum. (4) Terminal varicosities, the true anatomical ending of an axon, are often devoid of Schwann cell sheath, are packed with vesicles, rarely contain microtubules or neurofilaments, and lie close to a muscle cell: the gap is often reduced to similar to 10 nm. (5) Schwann cells accompany the axons within the muscle strands. Unlike the area of the axonal profiles, the area of glial sheath changes little along the length of the nerve fibre, except towards its end. (6) The Schwann cell sheath around a varicosity is often incomplete; the area of the axolemma thus exposed is covered by the basal lamina, and is here referred to as a 'window'. While some varicosities have a window only a few tens of nanometres in width, others have more than one window, and some are devoid of Schwann cell altogether, so that their entire axolemma is in contact with the basal lamina. The Schwann cell never extends beyond the axon, whereas very often (and possibly always) the axon extends beyond the Schwann cell. (7) Intervaricose segments vary in length and diameter, the narrowest ones accompanying the more clear-cut varicosities. Some intervaricose segments are as small as 50 nm in diameter, contain a single microtubule and lack a Schwann cell sheath. Others, sheathed by a Schwann cell, contain a single neurofilament or no organelles at all. (8) Specialized contacts between an axon and a muscle cell (neuro-muscular junctions) are abundant and are identified by four features: the axon is a varicosity packed with vesicles; the axolemma is exposed (presence of a window); the distance between the two membranes ranges between 10 and 100 nm, mostly 30-50 nm; and the intercellular gap excludes fibrils, such as collagen, but is occupied by a single basal lamina. Any of these parameters, however, can also occur 'uncoupled' (windows on intervaricose segments; varicosities without a window; exposed axolemma far from a muscle cell). (9) There are no direct contacts between axons. Even when they run close to each other within a bundle, they are always separated by a Schwann cell process. (10) The muscle cell membrane is concave beneath the varicosities; however, the muscle cell ultrastructural features in the region of the neuro-muscular junction are not different from those in other regions of the cell.(11) On average there is more than one neuro-muscular junction per muscle cell, and examples of muscle cells receiving multiple nerve endings from one or from two axons are picked up by the serial sections. (12) A striking feature of the bladder innervation is the variability of its ultrastructural parameters. The bladder innervation does not appear to be built on a rigid structural plan, and the notion of 'loose-patterned innervation' is presented.