英语听力文摘 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 poke themselves with a sharp object after reading this Moment of Science. But the next time you accidentally get poked 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 fibers 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.
