英语听力文摘 English Digest 200、疼痛感受器

　　Hey! and then…Ouch!
伤害性刺激作用于末梢神经引起神经兴奋电活动，沿着脊髓传人神经纤维中的细纤维(A和c纤维)传人脊髓，进而引起痛觉。痛觉是由于痛觉感受器受刺激而诱发的，其他感受器受到刺激产生相应的感觉，并非痛觉。人体内痛觉的传导依赖于机体受刺激侧对侧脊髓前外侧1／4象限内上行神经纤维构成的传导束的功能完整性。先天Jf生痛觉缺如的起因与痛觉相关的脊髓传人神经纤维的缺乏有关。参与痛觉产生的高级神经中枢为丘脑和大脑皮质，这些部位的损伤可以引起痛觉减弱。
'Hey! and then…Ouch!' on this Moment of Science.

　　One thing we don’t want anyone to do is poke¹ themselves with a sharp object after reading this Moment of Science. But the next time you accidentally get poked² you might notice something interesting.
Say you reach into a pile of clothes where a needle is sticking up. If you are able to reflect for a moment as you are sucking your fingertip, you may realize that you have had two separate sensations.
The first of these is what we might think of as the “hey!” sensation. It conveys the information that something startling has happened to your finger, and that thing is unpleasant. A moment after that comes a deeper-down feeling of pain. This latter sensation might be called the “ouch!” It’s not startling so much as just plain bad.
What’s going on here?
In fact, there are several different kinds of fibers³ that send pain information to your brain. These are called “nociceptors,” and they respond not only to pins but to heat, cold, chemical changes, and other dangers. These receptors send their information through two different kinds of fibers: the large, fast “A” fibers, and the smaller, slower “C” fibers.
Because they are naturally coated with a conductive substance, “A” fibers transmit messages at about 330 feet per second, whereas “C” fibers can only handle about six-and-one-half feet per second.
The delay some people can distinguish between “Hey!” and “Ouch!” is thought to be due to this time lag. It also makes sense that the faster “A” fibers would be the ones whose job it is to get you to pull your finger away right now.

1 poke   

n.刺，戳，袋；vt.拨开，刺，戳；vi.戳，刺，捅，搜索，伸出，行动散慢

参考例句：

• We never thought she would poke her nose into this.想不到她会插上一手。
• Don't poke fun at me.别拿我凑趣儿。

2 poked   

v.伸出( poke的过去式和过去分词 )；戳出；拨弄；与（某人）性交

参考例句：

• She poked him in the ribs with her elbow. 她用胳膊肘顶他的肋部。
• His elbow poked out through his torn shirt sleeve. 他的胳膊从衬衫的破袖子中露了出来。 来自《简明英汉词典》

3 fibers   

光纤( fiber的名词复数 )； （织物的）质地； 纤维，纤维物质

参考例句：

• Thesolution of collagen-PVA was wet spined with the sodium sulfate as coagulant and collagen-PVA composite fibers were prepared. 在此基础上，以硫酸钠为凝固剂，对胶原-PVA共混溶液进行湿法纺丝，制备了胶原-PVA复合纤维。
• Sympathetic fibers are distributed to all regions of the heart. 交感神经纤维分布于心脏的所有部分。