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qingqinghu

The chemical adenosine is released by brain cells when those cells are active.
Adenosine then binds to more and more sites on cells in certain areas of the
brain, as the total amount released gradually increases during wakefulness.
During sleep, the number of sites to which adenosine is bound decreases. Some
researchers have hypothesized that it is the cumulative binding of adenosine to a
large number of sites that causes the onset of sleep.

Which of the following, if true, provides the most support for the researchers’
hypothesis?

A Even after long periods of sleep when adenosine is at its lowest concen-
 tration in the brain, the number of brain cells bound with adenosine remains
 very large.
B Caffeine, which has the effect of making people remain wakeful, is known to
 interfere with the binding of adenosine to sites on brain cells.
C Besides binding to sites in the brain, adenosine is known to be involved in
 biochemical reactions throughout the body.
D Some areas of the brain that are relatively inactive nonetheless release
 some adenosine.
E Stress resulting from a dangerous situation can preserve wakefulness even
 when brain levels of bound adenosine are high.
                              答案是B, onset of sleep，那个onset  是理解为开始吗？如果是这样．那么光看那个hypothesis，我对B选项没有问题．

但是我怎么就看不懂在提出假设前的那一段话和那个假设有什么关系呢？估计是我理解能力太差了．麻烦哪位帮忙讲讲．

gonghao

The chemical adenosine is released by brain cells when those cells are active.
Adenosine then binds to more and more sites on cells in certain areas of the
brain, as the total amount released gradually increases during wakefulness.
During sleep, the number of sites to which adenosine is bound decreases. Some
researchers have hypothesized that it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep.

化学物质a是由一些激活状态的大脑细胞释放的。当醒的时候呢，总量上升；物质a接下来和许多许多的大脑特定区域的细胞绑定。

当睡的时候，对物质a限制的地区数量减少了，也就是说不限制的地方就多了（和之前特定的区域相比）。

一些科学家就假设，是物质a在大片地区的积蓄导致了睡眠的触发。【如果是特定部位蓄积就是醒，大面积就是睡】

问加强

找个说 ：的确是物质a的大面积的分部造成了睡眠

B，咖啡因－－ 影响了物质a的分布－－－ 从而不能大面积分部－－－ 不能睡觉

qingqinghu

谢谢，但是我还是没明白During sleep, the number of sites to which adenosine is bound decreases

当睡的时候，对物质a限制的地区数量减少了，也就是说不限制的地方就多了（和之前特定的区域相比）。

这里的bound 是理解为限制吗？我一直理解为bind 的过去分词，而且前面也是说　bind 到很多的区域．

所以我对科学家提出的假设和前面一段的推理关系很困惑．

gonghao

I'm sorry

解释有点偏差

应该是：睡觉的时候，物质a进行绑定的区域少了。这里的sites和上面所说的特定区域的sites是对应的。

醒的时候，物质a是和许多许多的大脑特定区域的细胞绑定。

因此，如果在特定区域的物质a减少，而在更大范围内的sites的物质a增加的话，就符合睡眠的条件，【特定区域的物质a的绑定减少就睡眠，特定区域物质a的绑定增加就醒着】

qingqinghu

我想了好久,觉得科学家的假设是这个意思:物质A 累积的绑定到一些区域就会导致睡觉.这样就可以解释睡觉时A绑定的区域变少.

和楼上解释的应该是一个意思．就是说绑定的sites 变少，某些A物质累积的绑定到一些sites 上了．

希望这回理解对了．

hsyeng

清醒的時候逐漸增加 睡覺中逐漸減少 所以推論 是增加到一個很大量時就會開始睡覺這個動作
(可以想像成睡覺時減少到零就醒過來繼續增加增加到一個極大值就睡著)

所以caffeine可以interfere with the binding 使得不會增加 也就不會那麼想睡覺

kenworth

类似物理学里LC震荡电路中2组变量之间此消彼的关系。

rio

还是不懂。。。

panglin

ding............

hello55olleh

以下是引用hsyeng在2006-8-16 16:16:00的发言：

清醒的時候逐漸增加 睡覺中逐漸減少 所以推論 是增加到一個很大量時就會開始睡覺這個動作
(可以想像成睡覺時減少到零就醒過來繼續增加增加到一個極大值就睡著)

所以caffeine可以interfere with the binding 使得不會增加 也就不會那麼想睡覺

不懂不懂

B干吗突然说咖啡因呀？不是无关么？