广泛的托福阅读背景知识积累，有助于托福阅读速度和准确率的提升。托福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 discovered that the same receptors that exist on the tongue to taste bitter substances are also found on the smooth muscle of the lungs.
　　Researchers were studying the receptors on smooth lung muscles that regulate contraction and relaxation of theairways. That’s when they made the discovery—which was so unexpected that the researchers themselves were skeptical.
　　Finally， they became convinced that the receptors were really there， though not clustered in taste buds as they are on the tongue. The scientists then exposed human and mouse airways to various bitter compounds to gauge the effects.
　　Many toxic compounds are bitter,so the researchers expected the lung muscle to tense up and contract—to compel the breather to move away from whatever was bitter and perhaps toxic. But， in a second surprise， bitter compounds relaxed and opened airways better than any existing asthma drug. The study is in the journal Nature Medicine. [Deepak Deshpande et al.， “Bitter taste receptors on airway smooth muscle bronchodilate by localized calcium signaling and reverse obstruction”]
　　Researchers will continue to search for the role of the receptors. Meanwhile， the work represents a surprising new lead in the search for drugs to treat asthma， emphysema or chronic bronchitis.
　　—Cynthia Graber