托福[微博]阅读文章分为自然科学、人文科学、互联网等几大类，如果同学们平时能对这些种类的文章都有所涉猎，托福阅读考试中遇到相关的话题就会有非常熟悉的感觉。下面给大家提供一篇关于人类味觉系统的背景材料，希望能拓宽同学们的阅读面。

　　Take a deep breath. Taste anything? Actually，your lungs may. Because scientists have discoveredthat the same receptors that exist on the tongue totaste bitter substances are also found on thesmooth muscle of the lungs。

　　Researchers were studying the receptors on smooth lung muscles that regulatecontraction and relaxation of theairways. That’s when they made the discovery—which was sounexpected that the researchers themselves were skeptical。

　　Finally， they became convinced that the receptors were really there， though notclustered in taste buds as they are on the tongue. The scientists then exposed human andmouse airways to various bitter compounds to gauge the effects。

　　Many toxic compounds are bitter，so the researchers expected the lung muscle to tense upand contract—to compel the breather to move away from whatever was bitter and perhapstoxic. But， in a second surprise， bitter compounds relaxed and opened airways better thanany existing asthma drug. The study is in the journal Nature Medicine. [Deepak Deshpande etal.， “Bitter taste receptors on airway smooth muscle bronchodilate by localized calciumsignaling and reverse obstruction”]

　　Researchers will continue to search for the role of the receptors. Meanwhile， the workrepresents a surprising new lead in the search for drugs to treat asthma， emphysema orchronic bronchitis。

　　—Cynthia Graber