How is the cell membrane involved in cell communication?
The Extracellular Matrix
I'm not exactly an expert but more like a jack-of-all trades, but far as I know, most, if not all animal cells have something called extracellular matrix in the outer region of the cell membrane. It is a combination of various cell receptors in the cell membrane usually made up of sugars and proteins. These receptors play a key role not only in cell identification through antigens (the main basis for antibody production of the immune system), but also as binding sites for chemical messengers like hormones. In effect, these binding sites allow a cell to receive information from other cells.