query: How many olfactory sensors do humans have?
passage: Olfactory receptor
There are a large number of different odor receptors, with as many as 1,000 in the mammalian genome which represents approximately 3% of the genes in the genome. However, not all of these potential odor receptor genes are expressed and functional. According to an analysis of data derived from the Human Genome Project, humans have approximately 400 functional genes coding for olfactory receptors, and the remaining 600 candidates are pseudogenes.[26]
passage: Linda B. Buck
In her landmark paper published in 1991 with Richard Axel, Linda Buck discovered hundreds of genes code for the odorant sensors located in the olfactory neurons of our noses. Each receptor is a protein that changes when an odor attaches to the receptor, causing an electrical signal to be sent to the brain. Differences between odorant sensors mean that certain odors cause a signal to be released from a certain receptor. We are then able to interpret varying signals from our receptors as specific scents. To do this, Buck and Axel cloned olfactory receptors, showing that they belong to the family of G protein-coupled receptors. By analyzing rat DNA, they estimated that there were approximately one thousand different genes for olfactory receptors in the mammalian genome. This research opened the door to the genetic and molecular analysis of the mechanisms of olfaction. In their later work, Buck and Axel have shown that each olfactory receptor neuron remarkably only expresses one kind of olfactory receptor protein and that the input from all neurons expressing the same receptor is collected by a single dedicated glomerulus of the olfactory bulb.