Nose & Smelling
The nose
A nose houses the nostrils, or nares, which admit and expel air for respiration. In most mammals, it also houses the nosehair, which catch airborne particles and prevent them from reaching the lungs. Within and behind the nose is the olfactory mucosa and the sinuses. Behind the nasal cavity, air passes through the pharynx, shared with the digestive system, and then into the rest of the respiratory system. In humans, the nose is located centrally on the face; on most other mammals, it is on the upper tip of the snout.
As an interface between the body and the external world, the nose and associated structures frequently perform additional functions concerned with conditioning entering air (for instance, by warming and/or humidifying it) and by reclaiming moisture from the air before it is exhaled (as occurs most efficiently in camels).
In most mammals, the nose is the primary organ for smelling. As the animal sniffs, the air flows through the nose and over structures called turbinates in the nasal cavity. The turbulence caused by this disruption slows the air and directs it toward the olfactory epithelium. At the surface of the olfactory epithelium, odor molecules carried by the air contact olfactory receptor neurons which transduce the features of the molecule into electrical impulses in the brain.
In cetaceans (whales & dolphins), the nose has been reduced to the nostrils, which have migrated to the top of the head, producing a more streamlined body shape and the ability to breathe while mostly submerged. Conversely, the elephant's nose has become elaborated into a long, muscular, manipulative organ called the trunk.