Sarnat H B, Netsky M G
Can J Neurol Sci. 1985 Nov;12(4):296-302. doi: 10.1017/s031716710003537x.
The planarian is the simplest living animal having a body plan of bilateral symmetry and cephalization. The brain of these free-living flatworms is a bilobed structure with a cortex of nerve cells and a core of nerve fibres including some that decussate to form commissures. Special sensory input from chemoreceptors, photoreceptor cells of primitive eyes, and tactile receptors are integrated to provide motor responses of the entire body, and local reflexes. Many morphological, electrophysiological, and pharmacological features of planarian neurons, as well as synaptic organization, are reminiscent of the vertebrate brain. Multipolar neurons and dendritic spines are rare in higher invertebrates, but are found in the planarian. Several neurotransmitter substances identified in the human brain also occur in the planarian nervous system. The planarian evolved before the divergence of the phylogenetic line leading to vertebrates. This simple worm therefore is suggested as a living example of the early evolution of the vertebrate brain. An extraordinary plasticity and regenerative capacity, and sensitivity to neurotoxins, provide unique opportunities for studying the reorganization of the nervous system after injury. Study of this simple organism may also contribute to a better understanding of the evolution of the human nervous system.
涡虫是具有两侧对称身体结构和头部化的最简单的活体动物。这些自由生活的扁虫的大脑是一个双叶结构，有神经细胞皮层和神经纤维核心，其中一些神经纤维交叉形成连合。来自化学感受器、原始眼的光感受器细胞和触觉感受器的特殊感觉输入被整合起来，以提供全身的运动反应和局部反射。涡虫神经元的许多形态学、电生理学和药理学特征以及突触组织，都让人联想到脊椎动物的大脑。多极神经元和树突棘在高等无脊椎动物中很少见，但在涡虫中却有发现。在人类大脑中鉴定出的几种神经递质物质也存在于涡虫神经系统中。涡虫在导致脊椎动物的系统发育线分歧之前就已经进化出来了。因此，这种简单的蠕虫被认为是脊椎动物大脑早期进化的一个活例子。其非凡的可塑性和再生能力以及对神经毒素的敏感性，为研究损伤后神经系统的重组提供了独特的机会。对这种简单生物体的研究也可能有助于更好地理解人类神经系统的进化。
