How do nerves work? - Elliot Krane

神经是如何工作的？ - Elliot Krane

翻译人员: Eva Cao 校对人员: Geoff Chen

How do nerves work?

神经是如何工作的？

Are nerves simply the wires in the body

神经只是人体中的电线吗？

that conduct electricity, like the wires in the walls of your home

像是家里墙壁中的电线导电吗？

or in your computer?

或像计算机中的电线？

This is an analogy often made,

通常我们会把神经比作电线，

but the reality is that nerves have a much more complex job in the body.

其实，神经在人体内的功能复杂多了。

They are not just the wires, but the cells that are the sensors,

它们不只是电线， 也是具有感应功能的细胞，

detectors of the external and internal world,

是体内和体外的世界的探测器，

the transducers that convert information to electrical impulses,

是能够将信息转换为电冲动的传导器，

the wires that transmit these impulses,

是传递这些电冲动的电线，

the transistors that gate the information

是阻截信息的晶体管，

and turn up or down the volume-

能上调或下调信息量，

and finally, the activators that take that information

最后，它是收取信息的启动装置，

and cause it to have an effect on other organs.

对其他器官产生效应。

Consider this. Your mother gently strokes your forearm

設想看看，當母亲轻轻抚摸你的手臂，

and you react with pleasure.

你的反应是愉悦的。

Or a spider crawls on your forearm and you startle and slap it off.

或者，当一只蜘蛛爬到你的手臂上， 你受到惊吓，把它拍掉。

Or you brush your forearm against a hot rack while removing a cake from the oven

或者，当你从烤箱取出蛋糕时， 手臂碰到了炙热的烤架，

and you immediately recoil.

你会马上收回来。

Light touch produced pleasure, fear, or pain.

轻触分别导致了愉悦、 恐惧，或疼痛。

How can one kind of cell have so many functions?

一类细胞怎么会具有这么多功能呢？

Nerves are in fact bundles of cells called neurons

神经其实是捆绑在一起的神经细胞，

and each of these neurons is highly specialized to carry nerve impulses,

每一个神经细胞高度专一传递神经冲动，

their form of electricity,

神经冲动可以比作是电流，

in response to only one kind of stimulus, and in only one direction.

一个神经细胞只对一种刺激作单向反应。

The nerve impulse starts with a receptor,

神经冲动启动从受体开始，

a specialized part of each nerve,

受体是神经细胞一个专门部分

where the electrical impulse begins.

是电冲动的开始位置。

One nerve's receptor might be a thermal receptor,

有的神经受体可能是感受温度的，

designed only to respond to a rapid increase in temperature.

只在温度突然上升时反应。

Another receptor type is attached to the hairs of the forearm,

有的受体连接到前臂的毛发

detecting movement of those hairs, such as when a spider crawls on your skin.

它们探测毛发的运动， 比如蜘蛛在皮肤上的爬行时毛发的变化。

Yet another kind of neuron is low-threshold mechanoreceptor,

还有一类神经细胞是很敏感的机械受体，

activated by light touch.

通过轻触激活。

Each of these neurons then carry their specific information:

每一个神经细胞传递他们接受的特定信息：

pain, warning, pleasure.

疼痛，警告，乐趣。

And that information is projected to specific areas of the brain

把信息投射到大脑的特定区域，

and that is the electrical impulse.

这就是是电冲动。

The inside of a nerve is a fluid that is very rich in the ion potassium.

神经内部的液体含丰富的钾离子，

It is 20 times higher than in the fluid outside the nerve

浓度是神经外的 20 倍之多

while that outside fluid has 10 times more sodium than the inside of a nerve.

神经外的液体含高浓度钠例子， 是神经内的 10 倍。

This imbalance between sodium outside and potassium inside the cell

细胞内外之间钾钠不平衡

results in the inside of the nerve having a negative electrical charge

导致神经内带负电荷

relative to the outside of the nerve,

相对神经外部，

about equal to -70 or -80 millivolts.

相当于负 70 或 80 毫伏。

This is called the nerve's resting potential.

这称为神经静息电位。

But in response to that stimulus the nerve is designed to detect,

一旦神经探测到信息被激活

pores in the cell wall near the receptor of the cell open.

受体附近的细胞膜会打开小孔。

These pores are specialized protein channels

这些小孔是特殊的蛋白通道，

that are designed to let sodium rush into the nerve.

作用是让外部的钠离子进入神经内。

The sodium ions rush down their concentration gradient,

钠离子顺浓度梯度快速移动，

and when they do, the inside of the nerve becomes more positively charged-

此时，神经内部就带正电荷，

about +40 millivolts.

约 是 40 的毫伏。

While this happens, initially in the nerve right around the receptor,

一开始，受体附近的细胞会有这个变化，

if the change in the nerve's electrical charge is great enough,

如果神经的电荷的变化足够大，

if it reaches what is called threshold,

达到了所谓 “阈值”，

the nearby sodium ion channels open, and then the ones nearby those,

会让周围细胞的钠离子通道打开， 以至于更大范围的钠离子的开启，

and so on, and so forth,

如此传递下去。

so that the positivity spreads along the nerve's membrane

这样一来，正电荷覆盖了整个神经，

to the nerve's cell body

从膜到细胞体，

and then along the nerve's long, thread-like extension, the axon.

也覆盖了细长的、如同棉线一样的延伸部分，轴突。

Meanwhile, potassium ion channels open,

同时，钾离子通道打开了，

potassium rushes out of the nerve,

钾离子从神经内流出，

and the membrane voltage returns to normal.

膜电位从而恢复正常，

Actually, overshooting it a bit.

事实上，还矫枉过正。

And during this overshoot,

点位矫正过头时，

the nerve is resistant to further depolarization-it is refractory,

神经不能再被去极化 ﹣ 此时神经是麻木的，

which prevents the nerve electrical impulse from traveling backwards.

防止了电冲动往回走。

Then, ion pumps pump the sodium back back out of the nerve,

然后，离子泵把神经内的钠离子泵到外面，

and the potassium back into the nerve,

同时，钾离子回到神经内，

restoring the nerve to its normal resting state.

神经恢复到正常的静息电位。

The end of the nerve, the end of the axon,

神经端和轴突端，

communicates with the nerve's target.

与目标沟通。

This target will be other nerves in a specialized area of the spinal cord,

目标可以是脊髓某一区域的的其他神经，

to be processed and then transmitted up to the brain.

信息处理后传达到大脑。

Or the nerve's target may be another organ, such as a muscle.

神经的目标可能是另一个器官，比如肌肉。

When the electrical impulse reaches the end of the nerve,

当电冲动到达神经端

small vesicles, or packets, containing chemical neurotransmitters,

含有化学神经传递物质的小液泡，或小颗粒，

are released by the nerve and rapidly interact with the nerve's target.

从神经中释放出来，快速作用于目标神经。

This process is called synaptic transmission,

此过程称为突触传输，

because the connection between the nerve and the next object in the chain

因为传输链中，神经与下一个神经连接的部位

is called a synapse. And it is here, in this synapse,

被称为突触。就在这里，在这个突触中，

that the neuron's electrical information can be modulated,

神经元电信息可能会被调节，

amplified,

被放大，

blocked altogether

被全部拦截，

or translated to another informational process.