For now, just picture it in this simple way as a molecule, usually a protein, that's embedded in the cell membrane and many receptors have a part of them that is extracellular.

现在,我只把这种分子图示出来,受体通常是一种蛋白质,它们镶嵌在细胞膜上,很多受体还有部分结构露在细胞外

耶鲁公开课 - 生物医学工程探索课程节选