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  3. The sensation of pain cannot accurately be described as "located" at the point of an injury, or, for that matter, in any one pla

The sensation of pain cannot accurately be described as "located" at the point of an injury, or, for that matter, in any one pla

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问题     The sensation of pain cannot accurately 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 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 pain signals that do not originate in the nervous sys- tern. Aspirin and other similar drugs(such as indomethacin and ibuprofen)keep prostaglandins from being made by interfering with an enzyme known as prostaglandin synthetase, or cyclooxy- genase. The drugs’ effectiveness against pain is proportional to their success in blocking this enzyme at the site of injury.
    From nerve endings at the injury, pain signals move to nerves feeding into the spinal cord. The long, tubular membranes of nerve cells carry electrical impulses. When 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 novo-caine and xylocaine work by blocking the electrical transmission along nerves in a particular area. They inhibit the flow of sodium ions through the membranes, making the nerves electrically quiescent; thus no pain signals are sent to the spinal cord or to the brain.
    Recent discoveries in the study of pain have involved the brain itself—the supervising organ that notices pain signals and that sends messages down to the spinal cord to regulate incoming pain traffic. Endorphins-—the brain ’ s own morphine—are a class of small peptides that help to block pain signals within the brain itself. The presence of endor- phins may also help to explain differences in response to pain signals, since individuals seem to differ in their ability to produce endorphins. It now appears that a number of techniques for blocking chronic pain—such as acupuncture and electrical stimulation of the central brain stem—involve the release of endorphins in the brain and spinal cord.
Of the following, which is most likely attributable to the effect of endorphins as described in the passage?
选项 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 anesthetic, an injured person reports relief in the anesthetized area.
D、After being given aspirin, a child with a badly scraped elbow feels better.
E、After acupuncture, a patient with chronic back pain reports that the pain is much less severe.
答案E
解析 哪一个最像是内啡肽的作用?该物质作用在第四段被明确给出，并举了例证。∴E正确。针刺后，慢性背痛患者说疼痛减轻。符合原文L53—58。A、B、C、D都是文章别处内容，和内啡肽的作用无关。
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