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The nose is the hollow protuberance in the face that admits air for respiration and that contains sensory receptors for odor detection. The ability to detect odors, the sense of smell, is also called olfaction.
Structure and Function
The Human Nose
The human nose is a prominent structure in the center of the face. The firm foundation of the nose is composed of bone at the upper portion, and cartilage at the lower portion. The tip of the nose and the nostrils are supported by cartilage, whereas the ridge of nose that lays between the eyes is supported by bone. Depending on age, ethnic group, and individual variation the mid-portion of the nose may be supported by either bone or cartilage. Examination of the nose readily reveals the level where the unyielding bony support changes to to the softer, moveable cartilage.
Every normal nose is covered by skin and lined by a thin tissue called mucosa. Unlike skin, mucosa is neither "waterproof" or dry, but glistens with moisture and easily absorbs substances from its surface. The nostrils are lined by skin on the outside and on the rim of their interiors.
The shape of the nose changes dramatically from infancy to adulthood. Newborn infants breathe through the nose, and the nose of young infants has a short and relatively open interior structure. The size of the nose increases somewhat throughout life, and the adult shape of the nose is usually reached by late adolescence.
The foundation of the nose is made up partly by bone and partly by cartilage.
The nose has an excellent blood supply. The benefit of high blood flow to the nasal mucosa is the increased ability for the nose to warm the air inhaled through the nostrils. This abundance of blood supply also promotes healing of nasal injuries and operations of the nose. Nosebleeds are common because of this generous blood supply, and the combination of the thin nasal lining and the well-supplied network of blood vessels can lead to dramatic nosebleeds from even minor breaks in the nasal lining.
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, 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.
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