The nose passes odor information to the olfactory cortex of the brain.
The sense of smell, known as olfaction, uses a sensory organ called the nose to pass information from smell to the olfactory cortex of the brain. Diffuse suspensions of relevant molecules, called odours, are analyzed through the nose using a molecular lock-and-key scheme in which odors are identified by their unique chemical signatures.
Sense evolved as a means of sensing survival-relevant information about the outside world, especially the evaluation of food. Smell is the oldest of the senses, with analogs dating back to the earliest animals 600 million years ago. One of the five primary senses, smell is most closely associated with the formation of memories.
Olfactory cells are neurons.
Olfactory receptor neurons, the cells responsible for smell, are located in a 1-by-2-inch band of tissue called the olfactory epithelium, located approximately 7 centimeters above and behind the nostrils. The human olfactory epithelium measures about 16 cm², unlike some dogs that measure 150 cm².
With advanced color vision, vision can be considered the main human sense: smell plays a more limited role, mainly related to feeding and sexual bonding. Olfactory receptor neurons are surrounded by supporting cells that excrete mucus, facilitating the uptake of odor molecules. The nostrils are covered with hairs to prevent the intrusion of unwanted organisms and inanimate material from environments.
Smell is the sense most associated with the formation of memories.
Olfactory receptor neurons, each of which can detect several molecules, project axons to the brain via the olfactory nerve. These projections converge on a small (~50 micron) structure called the olfactory bulb, which converges on only about 100 neurons. Considering the degree of convergence found in the olfactory portion of the nervous system, it may seem like a wonder that we can distinguish between so many odors, but the seemingly arbitrary firing patterns among the 100 neurons are enough to get the job done. Most humans can distinguish between several thousand odors and varying degrees of intensity and odor combinations.