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The sensation of pain cannot accurately1 be described as "located" at the point of an injury, or, for that matter, in any one place in the nerves or brain. Rather, pain signals-and pain relief-are delivered through a highly (5) complex interacting circuitry.

  When a cell is injured, a rush of prostaglandin's sensitizes nerve endings at the injury. Prostaglandins are chemicals produced in and released from virtually all mammalian cells when they are injured: these are the only (10) pain signals that do not originate in the nervous system. Aspirin2 and other similar drugs (such as indomethacin and ibuprofen) keep prostaglandins from being made by inter- fering with an enzyme3 known as prostaglandin synthetase, or cyclooxygenase. The drugs' effectiveness against pain is (15) proportional to their success in blocking this enzyme at the site of injury.

  From nerve endings at the injury, pain signais move to nerves feeding into the spinal4 cord. The long, tubular membranes5 of nerve cells carry electrical impulses. When (20) electrical impulses get to the spinal cord, a pain-signaling chemical known as substance P is released there.

  Substance P then excites nearby neurons to send impulses to the brain. Local anesthetics such as novocaine and xylocaine work by blocking the electrical transmission (25)along nerves in a particular area. They inhibit7 the flow of sodium8 ions through the membranes, making the nerves electrically quiescent9; thus no pain signals are sent to the spinal cord or to the brain.

  1. The passage is primarily concerned with

  (A) analyzing10 ways that enzymes11 and other chemicals influence how the body feels pain

  (B) describing the presence of endorphins in the brain and discussing ways the body blocks pain within the brain itself.

  (C) describing how pain signals are conveyed in the body and discussing ways in which the pain signals can be blocked
    (D) demonstrating that pain can be influenced by acupuncture12 and electrical stimulation13 of the central brain stem.

  (E) differentiating14 the kinds of pain that occur at different points in the body's nervous system.

  2. According to the passage, which of the following is one of the first things to occur when cells are injured?

  (A) The flow of electrical impulses through nerve cells at the site of the injury is broken.

  (B) The production of substance P traveling through nerve cells to the brain increases.

  (C) Endorphins begin to speed up the response of nerve cells at the site of the injury.

  (D) A flood of prostaglandins sensitizes nerve endings at the site of the injury.

  (E) Nerve cells connected to the spinal cord become electrically quiescent.

  3. Of the following, which is most likely attributable to the effect of endorphins as described in the passage?

  (A) After an injection of novocaine, a patient has no feeling in the area where the injection was given.

  (B) After taking ibuprofen, a person with a headache gets quick relief.

  (C) After receiving a local anesthetic6, an injured person reports relief in the anestherized area.

  (D) After being given aspirin, a child with a badly scraped elbow feels better.

  (E) After acupuncture, a patient with chronic15 back pain reports that the pain is much less severe.

  4. It can be inferred from the passage that if the prostaglandin synthetase is only partially16 blocked, which of the following is likely to be true?

  (A) Some endorphins will be produced, and some pain signals will be intensified17.

  (B) Some substance P is likely to be produced, so some pain signals will reach the brain.

  (C) Some sodium ions will be blocked, so some pain signals will not reach the brain.
     (D) Some prostaglandins will be produced, but production of substance P will be prevented.

  (E) Some peptides in the brain will receive pain signals and begin to regulate incoming pain traffic


1 accurately oJHyf     
  • It is hard to hit the ball accurately.准确地击中球很难。
  • Now scientists can forecast the weather accurately.现在科学家们能准确地预报天气。
2 aspirin 4yszpM     
  • The aspirin seems to quiet the headache.阿司匹林似乎使头痛减轻了。
  • She went into a chemist's and bought some aspirin.她进了一家药店,买了些阿司匹林。
3 enzyme cPozF     
  • Above a certain temperature,the enzyme molecule will become unfolded.超过一定温度,酶分子将会展开。
  • An enzyme that dissolves the fibrin of blood clots.能溶解血凝块中的纤维的酶。
4 spinal KFczS     
  • After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天,就已经使脊椎骨变得富有弹性了。
  • Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。
5 membranes 93ec26b8b1eb155ef0aeaa845da95972     
n.(动物或植物体内的)薄膜( membrane的名词复数 );隔膜;(可起防水、防风等作用的)膜状物
  • The waste material is placed in cells with permeable membranes. 废液置于有渗透膜的槽中。 来自辞典例句
  • The sarcoplasmic reticulum is a system of intracellular membranes. 肌浆网属于细胞内膜系统。 来自辞典例句
6 anesthetic 8wHz9     
  • He was given a general anesthetic.他被全身麻醉。
  • He was still under the influence of the anesthetic.他仍处在麻醉状态。
7 inhibit C7jxT     
  • Don't let ego and greed inhibit clear thinking and hard work.不要让自我和贪婪妨碍清晰的思维和刻苦的工作。
  • They passed a law to inhibit people from parking in the street.他们通过一项法令以阻止人们在街上停车。
8 sodium Hrpyc     
  • Out over the town the sodium lights were lit.在外面,全城的钠光灯都亮了。
  • Common salt is a compound of sodium and chlorine.食盐是钠和氯的复合物。
9 quiescent A0EzR     
  • It is unlikely that such an extremist organization will remain quiescent for long.这种过激的组织是不太可能长期沉默的。
  • Great distance in either time or space has wonderful power to lull and render quiescent the human mind.时间和空间上的远距离有一种奇妙的力量,可以使人的心灵平静。
10 analyzing be408cc8d92ec310bb6260bc127c162b     
v.分析;分析( analyze的现在分词 );分解;解释;对…进行心理分析n.分析
  • Analyzing the date of some socialist countries presents even greater problem s. 分析某些社会主义国家的统计数据,暴露出的问题甚至更大。 来自辞典例句
  • He undoubtedly was not far off the mark in analyzing its predictions. 当然,他对其预测所作的分析倒也八九不离十。 来自辞典例句
11 enzymes 7881ad8ce9c83424f7874e70266ed2d8     
n. 酶,酵素
  • It was said that washing powders containing enzymes remove stains more efficiently. 据说加酶洗衣粉除污更有效。
  • Among the enzymes which are particularly effective are pepsin, papain. 在酶当中特别有效的是胃朊酶、木瓜酶。
12 acupuncture 3zEznF     
  • Written records show that acupuncture dates back to the Song Dynasty.文字记载表明,宋朝就已经有了针灸。
  • It's known that acupuncture originated in China.众所周知,针灸起源于中国。
13 stimulation BuIwL     
  • The playgroup provides plenty of stimulation for the children.幼儿游戏组给孩子很多启发。
  • You don't get any intellectual stimulation in this job.你不能从这份工作中获得任何智力启发。
14 differentiating d3096d547199751d1b8d0cb8d931d402     
[计] 微分的
  • They succeed in differentiating the most commodity-like products. 在最通用的日用产品方面,它们也能独树一帜标新立异。
  • The simplest and most effective method of differentiating areas is to use different colours. 区别面状要素最简单而又行之有效的办法,是使用不同的颜色。
15 chronic BO9zl     
  • Famine differs from chronic malnutrition.饥荒不同于慢性营养不良。
  • Chronic poisoning may lead to death from inanition.慢性中毒也可能由虚弱导致死亡。
16 partially yL7xm     
  • The door was partially concealed by the drapes.门有一部分被门帘遮住了。
  • The police managed to restore calm and the curfew was partially lifted.警方设法恢复了平静,宵禁部分解除。
17 intensified 4b3b31dab91d010ec3f02bff8b189d1a     
v.(使)增强, (使)加剧( intensify的过去式和过去分词 )
  • Violence intensified during the night. 在夜间暴力活动加剧了。
  • The drought has intensified. 旱情加剧了。 来自《简明英汉词典》