寻找穿越大脑之路

马德里—我们的大脑像是茂密的森林——一个复杂的、难以穿越的、互相影响的神经元之林,调节着认知和行为。大挑战在于揭示它的神秘性,即找出神经元是如何构造的,又是如何互相联系的。我们对这一目标有多接近?

总体而言,构成神经元之林的数十亿神经元之间的信息交换通过两大高度专业化的结构发生:化学突触(主要)和所谓的缝隙连接(一类电突触的基底层)。化学突触传导包括释放特定的分子——散布于细胞间空间、与位于相邻神经元特定神经末梢互动的神经递质。在缝隙连接发出的电传导中,相邻神经元的细胞膜通过大约两纳米(一米的二十亿分之一)的缝隙分离,但包含连接相邻神经元细胞质的微小通道(缝隙连接),让小分子和电流得以传播和扩散。

分析大脑的主要问题在于其突触连接的极端复杂性。一个非常密集的过程网络占据着神经元细胞体、神经胶质(支持和保护神经元的细胞)和血管之间的空间。这类空间(神经毡,neuropil)占据了人类大脑皮层总体积的90—98%,每立方毫米神经毡大约包含十亿个突触。

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