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作者: qingqinghu 时间: 2006-7-15 13:21
标题: ＧＷＤ25 36

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．

作者: gonghao 时间: 2006-7-15 21:35

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

作者: qingqinghu 时间: 2006-7-16 08:44
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．

作者: gonghao 时间: 2006-7-16 09:27

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】

作者: qingqinghu 时间: 2006-7-16 10:43

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．

作者: hsyeng 时间: 2006-8-16 16:16

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

作者: kenworth 时间: 2006-10-30 16:10

类似物理学里LC震荡电路中2组变量之间此消彼的关系。

作者: rio 时间: 2006-11-26 18:49
还是不懂。。。

作者: panglin 时间: 2006-12-14 06:46
ding............

作者: hello55olleh 时间: 2006-12-17 19:01

以下是引用hsyeng在2006-8-16 16:16:00的发言：

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？

作者: hello55olleh 时间: 2006-12-21 20:05

作者: hello55olleh 时间: 2006-12-22 09:01
ding

作者: cccccc0 时间: 2007-1-4 16:02
当大脑的cells被激活的时候，A就会被这些cells释放。当在醒着的时候被释放的总数慢慢增加的时候，A然后就会邦在越来越多的cells的位置上。而当睡着的时候邦着A的的地方变少了。一些研究人员就假设

A邦定大量的site的积累的过程的时候导致了睡觉的发生

注意cumulative这个词，他时候过程；当邦定积累到一定的程度，邦定就会慢慢减少，那么就会导致睡觉的刚刚开始
A 无关，因为提干中的假设是说睡觉刚刚开始的时候，而A说after long periods of sleep

B 加强，说明A的邦定确实是和wakefullness或者是sleep相关的东西
C br无关
D inactive无关
E 说stress导致wakefullness或者是sleep的东西，否认了是A的邦定导致wakefullness或者是sleep的东西，所以削弱

作者: cccccc0 时间: 2007-1-4 16:03
不过我有个问题的，B中咖啡因的对wakefullness作用似乎与提干中说的不一样啊~~

作者: chenyudi 时间: 2007-3-18 20:02

当邦定积累到一定的程度，邦定就会慢慢减少，那么就会导致睡觉的刚刚开始

不同意这样理解,实际上应该是当人处于清醒状态中-非睡眠状态中, A绑定大脑中的区域的数量一直在累积. 而当人睡眠时,绑定区域的数量就减少了. 科学家就猜想绑定积累到一定时候就会引发睡眠. 并不是绑定减少才引起睡眠,而是睡眠时A绑定数量开始下降.

B说咖啡因干扰了A的绑定过程,也就是说咖啡因打乱了A的绑定, 使A的绑定数量无法增多, 从而让人保持清醒.

作者: phoenixwgq 时间: 2007-5-2 20:49
标题: 我这样理解

"as the total amount released gradually increases during wakefulness", 是说醒的时候释放的A增加，

"during sleepness, the nuber of sites to which a is bound decreases"是说睡的时候A可以bind的site减少。

A的释放增加，和site减少，是两回事。所谓site减少就是A物质bind to site减少，这个是在睡眠时发生的。所以科学家的假说是认为睡眠时bind这件事减少。

B就是说抑止bind这件事，刚好针对问题关键。

[此贴子已经被作者于2007-5-2 20:49:55编辑过]

作者: nancia 时间: 2009-9-2 14:18
顶

作者: qqiaoer 时间: 2010-3-13 12:21
大家可以看看这篇OG里面的阅读，作为一个背景知识，应该就容易理解这个逻辑题目了。
把OG关于咖啡因的文章贴到此，供大家参考。

Caffeine, the stimulant in coffee, has been called
“the most widely used psychoactive substance on Earth .”
Synder, Daly and Bruns have recently proposed that
caffeine affects behavior by countering the activity in
(5) the human brain of a naturally occurring chemical called
adenosine. Adenosine normally depresses neuron firing
in many areas of the brain. It apparently does this by
inhibiting the release of neurotransmitters, chemicals
that carry nerve impulses from one neuron to the next.
(10) Like many other agents that affect neuron firing,
adenosine must first bind to specific receptors on
neuronal membranes. There are at least two classes
of these receptors, which have been designated A1 and
A2. Snyder et al propose that caffeine, which is struc-
(15) turally similar to adenosine, is able to bind to both types
of receptors, which prevents adenosine from attaching
there and allows the neurons to fire more readily than
they otherwise would.
For many years, caffeine’s effects have been attri-
(20) buted to its inhibition of the production of phosphodi-
esterase, an enzyme that breaks down the chemical
called cyclic AMP.A number of neurotransmitters exert
their effects by first increasing cyclic AMP concentra-
tions in target neurons. Therefore, prolonged periods at
(25) the elevated concentrations, as might be brought about
by a phosphodiesterase inhibitor, could lead to a greater
amount of neuron firing and, consequently, to behav-
ioral stimulation. But Snyder et al point out that the
caffeine concentrations needed to inhibit the production
(30) of phosphodiesterase in the brain are much higher than
those that produce stimulation. Moreover, other com-
pounds that block phosphodiesterase’s activity are not
stimulants.
To buttress their case that caffeine acts instead by pre-
(35) venting adenosine binding, Snyder et al compared the
stimulatory effects of a series of caffeine derivatives with
their ability to dislodge adenosine from its receptors in
the brains of mice. “In general,” they reported, “the
ability of the compounds to compete at the receptors
(40) correlates with their ability to stimulate locomotion in
the mouse; i.e., the higher their capacity to bind at the
receptors, the higher their ability to stimulate locomo-
tion.” Theophylline, a close structural relative of caffeine
and the major stimulant in tea, was one of the most
(45) effective compounds in both regards.
There were some apparent exceptions to the general
correlation observed between adenosine-receptor binding
and stimulation. One of these was a compound called
3-isobuty1-1-methylxanthine(IBMX), which bound very
(50) well but actually depressed mouse locomotion. Snyder
et al suggest that this is not a major stumbling block to
their hypothesis. The problem is that the compound has
mixed effects in the brain, a not unusual occurrence with
psychoactive drugs. Even caffeine, which is generally
(55) known only for its stimulatory effects, displays this
property, depressing mouse locomotion at very low
concentrations and stimulating it at higher ones.

作者: qqiaoer 时间: 2010-3-13 12:31
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 thebrain, as the total amount released gradually increases during wakefulness. 随着化学物质Adenosine被脑细胞释放出来的数量在清醒时的逐步增加，A物质越来越多地绑定到大脑的某一区域（注意，这里的意思可不是说“绑定的多就清醒”如果错误理解成这样，那就会觉得前后有矛盾，而是“醒着的时候大脑释放A，A逐步越来越多地绑定”）

During sleep, the number of sites to which adenosine is bound decreases. 睡眠时，A物质被绑定的区域减少（我的理解是和前面那句话说的是一回事，A绑定的越来越多，所以可以给更多的A用来绑定的区域当然就少了）

Some researchers have hypothesized that it is the cumulative binding of adenosine to a
large number of sites that causes the onset of sleep.
结论：累计的A绑定到大脑某个区域的数量达到一个大的量，这个累积的绑定就引发了睡眠。
注意：THAT从句 that causes the onset of sleep修饰限定的是binding

所以这个题目B的含义和结论要论证的方向完全一致。

其实还是阅读理解的问题，我一开始也晕。

作者: 双鱼游 时间: 2010-10-1 22:37
顶楼上，解释的非常清楚

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