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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.
It can be inferred from the passage that if the prostaglandin synthetase is only partially blocked, which of the following is likely to be true?
选项 A、Some endorphins will be produced, and some pain signals will be intensified.
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.
答案B
解析 如果前列腺素合成只是部分受阻，下面哪个将会发生?前列腺素只部分受阻，意味着痛信号将向脊髓传播。∴B正确。一些P物质会产生，一些痛信号将抵达脑神经L28—31，这正是原文第三段内容。A．“endorphins”是否产生和痛信号如何并没有直接联系。C．一些钠离子被阻碍。这是使用局麻药的后果，和痛信号无直接联系。D．P物质制造将被阻止。说反了。E．peptides接收痛信号并调节痛传输。文中无。
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