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英海听涛

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喜欢科学,偏爱自然科学。也喜欢技术,儿时喜围观打锡壶的和锔盆锔锅的。当过工人,当过兵,第二故乡是湖南、广西和广东。

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我们为什么睡觉?  

2013-11-14 11:26:53|  分类: 生命与健康 |  标签: |举报 |字号 订阅

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(喜欢熬夜的朋友要注意一些了,呵呵。为了中英文对照的方便,分了较多的段落并加了段落编号。还有些地方没听出来,希望能得到指教。)

1)要说我们不理解困难的和复杂的东西如量子力学或暗物质这不奇怪,可是有些简单的东西我们也不懂。比如我们为什么睡眠?为什么我们差不多三分之一的生命是处于事实上瘫痪、失明和哑吧的状态?当然,我们之所以睡觉是因为我们困倦了,可是我们为什么会困倦?为什么它发生在大约16小时后而不是1小时或60小时后呢?

2)睡眠中我们的脑子并不是在休息,事实上当我们睡觉时脑中的网络处于非常有组织的活动中,它消耗的能量与我们清醒时几乎相当。我们现在还知道睡眠期间脑精心组织生产多种不同类型的分子:蛋白质、类固醇、胆固醇、脂筏、人生长激素等等还有很多。另一方面,如果你得不到足够的睡眠,如许多倒班工人一样,你会增加心脏病和某些癌症的风险。

3)可是我们为什么要睡觉呢?哦,几乎可以肯定,答案将是有许多原因,它们的重要程度也不一样。一些睡眠科学家说睡眠的最终目的是“修剪”或削弱你觉醒时建立的脑中联接。这意味着第二天你的脑不会因为有许多无关紧要的联接而过载。而其他的睡眠科学家指出有一项研究显示睡眠替换并巩固重要的记忆。某些新近的研究指出睡眠期间一些神经传导电脉冲的方向与我们清醒时的正常情况刚好相反,我们还不太清楚它们为什么这么做。

4)另外的当前研究说睡眠给予脑子一个机会,让它把日间产生的多种代谢废物冲洗出去。如果我们观察脑,会看到其中有许多解剖结构:神经细胞、支持神经细胞的胶质细胞、动脉、静脉、以及让脑飘浮在其中的脑脊液。人们往往忽略的是这些结构之间的空间、间隙、空隙,我们称之为细胞间隙(胞间隙),这些空间里充满了一种液体,称为脑脊液(CSF)。这些细胞间隙约占颅内容量的20%。

5)人脑重约1.5千克。这里有个问题:它完全是软绵绵粘糊糊又没有支撑结构的一个整体。所以一般来说脑的重量将会压垮并损坏脑底层的结构。因此脑脊液的一个重要作用就是浮起脑组织,这样一来脑的有效重量只有约25克,其底部的结构就不会被上部的重量压垮了。

6)不论任何时候,约有140毫升的脑脊液在脑的内部和周围以及脊髓中,然而你每天制造的脑脊液约有500毫升,所以它是边制造边吸收的。这意味着你有大量的“过剩”产能来制造额外的脑脊液。大部分脑脊液在细胞间隙里流通。

7)在睡眠期间脑细胞会收缩,这使得细胞间隙增加60%的容量,这也意味着在脑的空间里,当你睡眠时的脑脊液流量会增加到让人吃惊的20倍。很快地,白天积聚起来的脑代谢产生的废物在你睡眠时被滚滚而来的脑脊液的激流冲刷而去。

8)如今我们知道在某些情况下,脑中过量的蛋白质与多种多样的神经退行性疾病相关。例如,贝它淀粉样蛋白质与阿尔茨海默病有关。这些以及其他类似的蛋白质通常是存在于胞间隙中的。

9)在一项研究中,科学家发现特定的药物能使我们睡眠时大量增加的脑脊液的冲刷作用停止,作为一个直接后果,脑中不良化学物的水平会升高。也许使用别的药物能在我们清醒的状态下增加脑脊液的净化作用,降低不良化学物的水平,那我们在此过程中就可以清除废物了。

——《卡尔博士的科学伟大时刻》/《我们为什么睡觉》,ABC 2013/11/5

 

1)It makes sense that we don’t understand difficult and complicated stuff like quantum mechanics or dark energy, but we also don’t know simple stuff, such as why do we sleep, why do we spend about one third of our lives virtually paralysed as well as being blind and dumb? Sure, we sleep because we are sleepy but why do we get sleepy? And why after about sixteen hours? Why not one hour or sixty hours?

2)Now, it is not the brain in resting, in fact, when we sleep, networks in the brain undergo very organized patterns of activity and use almost as much energy as when we are awake. Now we also know that during sleep the brain orchestrates the manufacture of many different types of molecules: proteins, steroids, cholesterol, lipid rafts, human growth hormone and many more. And on the other hand, if you don’t get enough sleep, as happens to many shift-workers, you suffer increased risk of heart disease and some cancers.

3)But why do we sleep? Well, almost certainly it’ll turn out that there are many different reasons all of them ?? to vary degrees. So some sleep scientists claim that the ultimate purpose of sleep is to prune or weaken brain connections that you have made while you are awake, and so this means that the next day your brain won’t be overloaded with irrelevant memories. And other sleep scientists point to a research that suggests that sleep replaces and consolidates significant memories. And some recent research points out that during sleep some nerves send their electrical impulses in the opposite direction that they normally do when you are awake. We are not too sure why they do this. And other current research says that sleep gives the brain the opportunity to flush out the various metabolic waste products created during the day.

4)If you look at the brain, there are a lot of obvious anatomical stuff: the nerve cells, the glial cells that support the nerve cells; the arteries and the veins; and the cerebrospinal fluid or CSF that keeps the brain afloat. What is unappreciated is the space in-between these structures, the gap, the void, the so called interstitial space that is filled with the ?? liquid that is called CSF. This interstitial space makes up about twenty percent of the volume inside your skull.

5)Now the brain weighs about one and a half kilos. The trouble is that is all soft and squishy with virtually no structural integrity. So normally the weight of the brain would crash and damage all the structures at the bottom of the brain. So one very important role of the CSF, the cerebrospinal fluid is to ?? float the brain so that it’s effective weight is only about twenty-five grams and the stuff at the bottom doesn’t get damaged by the weight of the stuff above it.

6)At any given moment, there is about a hundred and forty mls of CSF in and about the brain and the spinal cord. However you make about five hundred mls of CSF each day so it is always being made and always being absorbed. This means that you have massive over capacity to make extra CSF and most of the CSF flows through the interstitial space.

7)During sleep the brain cells shrink and so the interstitial space increases by about sixty percent in volume. This means that in the case the brain, when you sleep the flow rate of the CSF increases by an astonishing twenty times. Suddently the waste products of brain metabolism that have built up during the day are whisk away by the raging torrent of cerebrospinal fluid when we are asleep.

8)Now we know that in some cases, excess quantities of proteins in the brain are linked to various neurodegenerative diseases. For example, the protein beta amyloid is linked to Alzheimer’s disease. These and many other similar proteins are normally preset in the interstitial space.

9)Purely as a research study the scientists found out that certain drugs could stop this flushing action of the massively increased flow rate of the CSF when we are asleep. As a direct result, this increased levels of nasty chemicals in the brain. Perhaps with different drugs they could increase the flushing actions of the CSF while we are awake and reduce the levels of these nasty chemicals and we could get de-wasted in the process.

-- Dr Karl’s Great Moments in Science / Why Do We Sleep? ABC 2013/11/5

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