The central nervous system of Loligo. I. The optic lobe.
The central nervous system of Loligo. I. The optic lobe.
复制标题
洛利戈的中枢神经系统。
DOI：
--
复制
发表时间：
1974
期刊：
影响因子：
--
通讯作者：
John Zachary Young
中科院分区：
文献类型：
--
作者：
John Zachary Young
视神经纤维以规则的方式投射到视叶上，在穿过交叉后精确地重新组合。在外丛状区，视神经纤维的末端与二级视细胞的树突接触。这些可能用于分类视觉输入，并且在解剖学上可以识别出四种类型：（1）最小的具有微小的圆形树突区域，与一个或几个视神经纤维接触。(2)还有更大的圆形场地。(3)许多细胞具有非常细长的树突状区域，每个树突状区域都朝一个方向笔直延伸，因此可能对边缘敏感。(4)最大的第二级视细胞有巨大的椭圆形树突状区域，几毫米长，定向在叶的长轴上。每种类型的场占据不同的水平，产生外丛状带的特征性分层。许多无长突细胞突起终止于外丛状层，有些非常小，具有限制的分支，另一些具有宽树，纤维先向内然后向外穿过几次。因此，有可能在小或大的视野区域上建立统一的兴奋或抑制条件。离心细胞的树突与轴突一起延伸到视网膜，分布在丛状带的各层。它们可以将兴奋或抑制区域的信息投射到视网膜上。第二级视细胞的轴突在视叶髓质的外部形成放射状柱。那些具有较小树突区域的细胞末端更浅，最大的树突区域大约在叶的一半。每一个柱状细胞的中心都有纤维和神经纤维，周围有多极和双极无长突细胞，它们的分支进入二级视细胞末梢之间的神经纤维。各种大小的水平多极单元连接列。三级视觉细胞将树突送入这些柱状物，将轴突送入叶的更深处，有些直接到达视束。因此，大细胞叶的巨细胞可以通过只涉及两个先前突触的视觉通路（以及不涉及任何突触的直接静态通路）激活。径向柱区域的中心是一个区域，其中许多连接是切向的。有越来越多的大细胞通过中央，许多可能是第四级视觉神经元。它们将轴突发送到叶内的其他地方或视束。从中央脑或对侧脑叶到达脑叶的纤维分布在该区域，并且也延伸到放射状柱。在许多离开视叶到其他中心的纤维束中，纤维保持精确的地形关系，视连合也是如此。这种规律性在传递到运动中心（脚叶和前基底叶）的束中尤其明显，但也可能存在于其他部位。因此，在整个系统的大部分区域中存在视野的规则映射。其他途径显示复杂的交织，例如颜色控制，其中的响应模式是不地形相关的视觉输入。
The optic nerve fibres project on to the optic lobe in a regular manner, being precisely re-assorted after passing through a chiasma. In the outer plexiform zone the optic nerve fibres end in contact with the dendrites of second-order visual cells. These presumably serve to classify the visual input and four types can be recognized anatomically: (1) The smallest have minute circular dendritic fields, in contact with one or few optic nerve fibres. (2) There are also larger circular fields. (3) Many cells have very elongated narrow dendritic fields each running straight in one direction and thus perhaps sensitive to edges. (4) The largest second-order visual cells have enormous oval dendritic fields, several millimetres long, orientated in the long axis of the lobe. Each type of field occupies a different level, producing the characteristic layering of the outer plexiform zone. Numerous amacrine cell processes end in the outer plexiform layer, some are very small with restricted branches, others have wide trees with fibres passing first inwards then outwards several times. There are thus possibilities of establishing uniform conditions of excitation or inhibition over small or large areas of the visual field. The dendrites of the centrifugal cells with axons passing to the retina spread in the various layers of the plexiform zone. They could serve to project information of the areas excited, or inhibited, out to the retina. The axons of the second-order visual cells form radial columns in the outer part of the medulla of the optic lobe. Those with the smaller dendritic fields end more superficially, the largest ones about half-way through the lobe. Each column contains fibres and neuropil at its centre, surrounded by multipolar and bipolar amacrine cells, whose branches enter the neuropil among the endings of the second-order visual cells. Horizontal multipolar cells of various sizes link the columns. Third-order visual cells send dendrites into these columns and axons deeper into the lobe, some directly to the optic tract. The giant cells of the magnocellular lobe can thus be activated by a visual pathway involving only two previous synapses (as well as by a direct static pathway involving none). Central to the zone of radial columns is a zone where many of the connexions are tangential. There is an increasing number of large cells passing centrally, many being presumably fourth-order visual neurons. They send axons either elsewhere within the lobe or to the optic tract. Fibres reaching the lobe from the central brain or opposite lobe are distributed in this region and also reach out into the radial columns. In many of the tracts leaving the optic lobes for other centres the fibres maintain precise topographical relations, as also do those of the optic commissure. This regularity is especially clear in the bundles that pass to the motor centres (peduncle lobes and anterior basal lobes) but may be present in others. There is thus a regular mapping of the visual field throughout much of the system. Other pathways show complex interweaving, for instance those for colour control, where the response pattern is not topographically related to the visual input.