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It is the coastal plain, and that provides, or that is the main highway out of Egypt or down to Egypt.
这就是海岸平原，它提供了或说它本身就是,离开埃及或者下埃及的主要通道。
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However, when that gate is opened, the sodium channel is now going to be incredibly selective and only let through sodium ions and no other type of ion.
但是，当闸门打开的时候，钠离子通道,将会有极高的选择性,不允许除钠离子以外的任何其它离子通过。
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The ones that are most important in physiology are ones that only allow ions to go through: sodium, potassium, chloride, calcium, bicarbonate.
在生理学上这种,只能允许某种离子通过的通道十分重要,这些离子包括钠离子,钾离子,氯离子,钙离子和碳酸氢根离子
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You can sit up the steps and in the aisles.
可以坐在阶梯上或通道中。
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Milton's blindness, the fact of his blindness, has shut out his view of the visible world, which would ordinarily present itself to him through the entrance of his eyes; and this shut-out will enable him, will help him, explore the invisible world of divine truth.
弥尔顿的失明，他失明的这个事实，遮住了,他看具体世界的目光，他通常是通过双眼,这个通道来看具体世界的，不过这种蒙蔽帮助了他，使他能够探索不可见世界中的神圣真理。
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He also had the idea that he would make it narrow enough so that when you're boarding an airplane you can still roll it down the aisle of the airplane-- it just fit perfectly.
他还想到要将把手弄的窄一点,以便登机进通道的时候,还能拖着箱子走-,这非常符合当时的需要。
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And all ion channels are selective for a single type of ion, and we can think about how that selectivity takes place, and that's where this idea of atomic radius is going to become very important.
所有的离子通道都是仅对某一种离子具有选择性的，而我们可以来想一想这种选择性是如何发生的，这也就是原子半径这个概念将会变得，非常重要的地方。
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We can already use that in terms of single ions to think about a really complex biological issue, which is to talk about ion channels.
我们已经能够仅仅凭借这个关于单个离子的原理,来讨论一个非常复杂的生物问题了，我们要讨论的就是离子通道。
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So, what happens, this is another view of a sodium channel, so this is actually looking a little bit more at the protein structure.
那么，这里发生了什么，这是钠离子通道的另一张图片，在这种蛋白质结构中,它看起来更复杂一点。
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Because if it was a neurotransmitter activated ion channel, what would happen when the neurotransmitter bound here?
因为假如这是一个,神经递质激活的离子通道,当神经递质结合于此的时候,会发生些什么呢
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And actually, a question that might come up, I just explained, the sodium channel, you might say, well, how do potassium channels work then, because I can understand how you can filter something big out, but how do you filter out something small.
实际上，可能大家会问一个问题，我刚解释过，钠离子通道，你可以说，好吧，那么钾离子通道该如何起作用呢，因为我可以理解你是如何把大东西过滤掉的，但是你如何把小东西过滤掉呢？
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For these purposes think about a channel, it only allows sodium to go through for example.
基于此目的,我们来讲离子通道,拿仅允许钠离子通过的通道作为例子
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That change happens because something gets triggered in the membrane, and what gets triggered is a voltage gated sodium channel, which is shown here.
变化的原因是膜上某些东西被触发了,被触发的是钠离子电压门控通道,展示在这儿了
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It has a gate on it and that gate is in open or close state depending on whether a ligand is present or not.
在这个通道上有个门,这个门是打开还是关闭,取决于配体到来与否
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That's shown functionally here but recovery means that this sodium channel becomes closed again.
在此展示了这项功能,恢复代表着钠离子通道再次关闭
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What all of these channels have is what's called a selectivity filter, so this filter filters out the type of ion that's going to be allowed through.
这些离子通道都有的一部分,就是所谓的选择性过滤器，这个过滤器,会滤过允许穿过的离子。
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So, that is just a quick example for some of you, you might be very familiar with ion channels, others might not know what these are, so I'll just tell you quite briefly that ion channels are these very massive transmembrane proteins.
这对你们中的某些人来说仅仅是个小例子，有些人可能已经非常熟悉离子通道这个概念了，但有些人可能还不清楚，那么就让我来简单地介绍一下离子通道,就是这些巨大的跨膜蛋白。
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many of these ion channels have this size exclusion pore, it's a very important part of them.
很多离子通道也都有这样的具有尺寸排斥性的小孔，这是它们非常重要的组成部分。
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And when we talk about any type of ion channel, there are just tons of different kinds of ion channels, and you can characterize them in a few different ways.
而当我们讨论任何一种离子通道时，离子通道有非常多种，你可以用几种不同的方法来描述它们。
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It can exist in - a gated ion channel - can exist in one or two states.
它们能够存在于,门控离子通道有一种或者两种状态
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So the influx of ions from the outside of the cell to the inside of And you can think of ion channels as being gated, by gated it means the gate can be closed and no ions are going through, as in this case here.
下面以离子从细胞外部流入内部,你可以把离子通道想象成是有闸门的，也就是说闸门可以关上,这时没有离子能通过，就像这种情况。
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If a ligand comes and interacts with a receptor, it opens up; In the presence of this ligand, if the ligand goes away, it closes.
如果配体与受体相互作用,在配体存在的情况下通道打开,如果配体脱离,通道就关闭
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Now, these are special channels in that they only allow certain molecules to pass through.
这种特殊的通道,只能允许特定的分子通过
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All cell membranes have these channels within them, and under their resting conditions sodium is moving from outside to inside, potassium's moving from inside to outside.
所有细胞膜上都有这种通道结构,在静息状态下,钠从细胞外流向细胞内,钾从细胞内流向细胞外
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There's a continuous path from the outside world right through the intestine.
从体外经由肠道的路径,是一条连贯的通道
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A state where it's closed, so imagine a channel with a lid on top of it; when it's closed nothing can go through the channel, when it's open then things can go through.
一种是闭合状态,想想一个有盖子的通道吧,当盖子合上的时候任何东西都不能通过,而打开时就畅通无阻
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Now, remember we talked about these last time, voltage-gated channels are channels that would allow the passage of sodium, in this case, but they can exist in two states, a closed state and an open state.
还记得我们上节课讨论过的吧,电压门控通道是,一种可以容许钠离子通过的通道,在这一例子中 电压门控通道有两种状态,关闭状态和开放状态
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The cells that take an electrical signal, which is coming down your nerve and convert it into a muscle contraction work this way, so 'neuro' nerve, muscle junctions act based on ligand-gated ion channels.
依靠相同的工作原理,细胞将来自于神经的,电信号传递到细胞收缩肌中,所以神经和肌肉关节运动,都基于配体门控离子通道
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Now, it's more complicated than that because it's not just sodium channels that are involved, there are potassium channels also, and the interplay between sodium channels opening and potassium channels opening, this is described in some detail in your book.
现在 事情更复杂了,因为这一过程不仅关系着钠离子通道,也关系着钾离子通道,以及钠离子通道和钾离子通道之间开关,的相互作用,书中有详细解释
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Now, sodium and potassium don't ordinarily move across membranes, they're charged molecules, they can't dissolve, they can't permeate through a cell membrane, but they go through because there are channels that allow them to pass through in the membrane.
钠和钾通常是不能跨过细胞膜的,它们都是带电粒子,它们不能溶解在细胞膜中,不能渗透通过细胞膜,但它们之所以能通过细胞膜,全赖膜上离子通道的作用
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