廣泛的托福閱讀背景知識積累，有助于托福閱讀速度和準確率的提升。托福閱讀文章分為自然科學、人文科學、互聯網等幾大類，如果同學們平時能對這些種類的文章都有所涉獵，托福閱讀考試中遇到相關的話題就會有非常熟悉的感覺。下面給大家提供一篇關于人類味覺系統的背景材料，希望能拓寬同學們的閱讀面。
　　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