Why nerves are bundles of fibers? - Experimental verification to the origin of the parallel structure

为什么神经是由大量纤维组成的束？这是后生动物多细胞组织的简单结果吗？这个幼稚的问题最终会触及到，神经系统适应了什么样的选择压力，或者在进化中获得了生存价值？还有，在适应气候变化的过程中受到了什么样的限制？信息的获取（即测量）不可避免地需要能量的耗散（准确地说是熵）。蟋蟀风感受器细胞的信息能量成本非常接近热力学理论的极限（0.7 kBT焦耳/比特）。本研究揭示的结果如下。1)对蟋蟀风感受器毛发的布朗运动进行光学测量，揭示了波动耗散定理在活体组织中的有效性。2)蟋蟀的感觉细胞对热噪声很敏感，因此作为一个非常差的信息元素，因为信噪比很低。3)本研究证实了在神经系统中，由于热噪声的存在，细胞很大程度上是随机的，求和平均原理是有效的，即平均值的信度依赖于样本量的平方根倒数。活细胞对热噪声的极高灵敏度并不是通过进化而达到的，而是追溯到生命起源的一种限制。资源的时空分布不均和生存环境的危害是信息传播速度加快的选择压力。受差信噪比约束的活细胞的生物解是并行传输的求和平均。

Why nerves are bundles of a large number of fibers? Is this a simple consequence of multi-cellular organization of metazoan life? This naive question will reaches, in the end, what type of selection pressure the nervous system was adaptive to or gaining a survival value in the evolution? and also what kind of constraints has been tied on the adaptation?Acquisition of information (i.e. measurement) inevitably requires dissipation of energy (entropy in accurate). Energy cost of information in cricket wind receptor cell was measured as very close to the limit of thermodynamic theory (0.7 kBT Joule/bit). Results revealed by this research are followings.1) Optical measurement of the Brownian motion of the cricket wind receptor hair revealed the validity of fluctuation-dissipation theorem in living tissue.2) Cricket sensory cell is sensitive to thermal noise and therefore operates as a very poor informational element because of low signal to noise ratio.3) The present study confirmed that the principle of summation average, i.e. reliability of mean value depends on inverse square root of sample size, is effective principle in the nervous system where cells are largely stochastic because of thermal noise.The extremely high sensitivity of living cell to thermal noise is not achieved by evolution, but this is rather constraint retroactively to the beginning of life. Spatio-temporally uneven distribution of resource and harm in living environment act as selection pressure for increase in transmission rate of information. Biological solution by living cells which are tied on the constraint of poor signal to noise ratio is the summation average by parallel transmission.