NOSE

Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration. In most mammals, it also houses the nosehairs, 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 next 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. Nose as a term may be used to designate the leading end of anything, such as an airplane.

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, 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.

Due to the special nature of the blood supply to the human nose and surrounding area, it is possible for retrograde infections from the nasal area to spread to the brain. For this reason, the area from the corners of the mouth to the bridge of the nose, including the nose and maxilla, is known to doctors as the danger triangle of the face.

All humans have a trace amount of magnetite in their noses, found in the ethmoid bone (between the eyes), possibly part of a rudimentary compass to allow direction finding relative to the earth's magnetic field. The human magnetoception is still very controversial, but some studies show that some people have the ability to orient themselves-even when blindfolded and removed from such external clues as sunlight-to within a few degrees of the North Pole, exactly as a compass does.

Sneeze

A sneeze is the semi-autonomous, convulsive expulsion of air from the nose and mouth. An unimpeded sneeze sends two to five thousand bacteria-filled droplets into the air. The medical name for sneezing is sternutation.

Sneezing is generally caused by irritation in the passages of the nose. Pollens, house dust, and other particles are usually harmless, but when they irritate the nose the body responds by expelling them from the nasal passages. The nose mistakes strong odors, sudden chills, bright lights (see photic sneeze reflex), and even orgasms in some people for nasal irritants, and it tries to defend itself with a sneeze.

It is almost impossible for a person to keep their eyelids open during a sneeze. The reflex of shutting the eyes serves no obvious purpose: the nerves serving the eyes and the nose are closely related, and stimuli to the one often trigger some response in the other.

Nose-picking

Nose-picking is the act of extracting mucus or foreign bodies from the nose with a finger. Compulsive nose-picking is known as rhinotillexomania

A nosebleed or nose bleed, medically known as epistaxis, is the relatively common occurrence of hemorrhage (bleeding) from the nose, usually noticed when it drains out through the nostrils. There are two types: anterior (the most common), and posterior (less common, and more severe).

All nosebleeds are due to tears in the mucosal lining and the many small blood vessels it contains. Fragility or injury may cause the tears, while inflammation, coagulation problems and other disorders may make the injury harder to repair.

Little's area

Little's area is an area within the nose near the nasal septum that is richly infiltrated with small capillaries. Inflammation of this area is a common cause of epistaxis (nasal bleeding).

Mucus

Mucus is a slippery secretion of the lining of various membranes in the body (mucous membranes). Mucus aids in the protection of the lungs by trapping foreign particles that enter the nose during normal breathing. Additionally, it prevents tissues from drying out.

Mucus is made by goblet cells in the mucous membranes that cover the surfaces of the membranes. It is made up of mucins and inorganic salts suspended in water.

In the digestive system, mucus is used as a lubricant for materials which must pass over membranes, e.g. food passing down the esophagus. In the respiratory system, it catches unknown matter and tries to prevent it from entering the body, especially in the nose. In the reproductive system, mucus aids the penis in entering the vagina during intercourse.

Mucus is a viscous colloid containing antiseptic enzymes (such as lysozyme) and immunoglobulins.

Increased mucus production in the respiratory tract is a symptom of many common diseases, such as the common cold. The presence of mucus in the nose and throat is normal, but increased quantities can impede comfortable breathing and must be cleared by blowing the nose or expectorating phlegm from the throat. Among the components of nasal mucus are tears.

NASAL CAVITY

The nasal cavity is a large air-filled space above and behind the nose in the middle of the face. The nasal cavity is important in warming and cleaning the air as it is inhaled. The nasal cavity also contains organs involved in olfaction.

The nasal cavity is enclosed by the nasal bone above and by the maxilla and ethmoid bone on the sides. The palate separates the nasal cavity from the mouth. To the front of the nasal cavity is the nose, while the back is continuous with the pharynx. The paranasal sinuses are connected to the nasal cavity through small orifices called ostia.

The nasal cavity is divided in two by a vertical fin called the nasal septum. On the sides of the nasal cavity are three horizontal outgrowths called turbinates or conchae (singular "concha"). These turbinates disrupt the airflow, directing air toward the olfactory epithelium on the surface of the turbinates and the septum. The vomeronasal organ is located at the back of the septum and has a role in pheromone detection.

Cilia and mucus along the inside wall of the nasal cavity trap and remove dust and germs from the air as it flows through the nasal cavity. The cilia move the mucus down the nasal cavity to the pharynx, where it can be swallowed.

There is a rich blood supply to the nasal cavity. In some animals, such as dogs, the capillary beds flowing through the nasal cavity help cool the blood flow to the brain.

Diseases of the nasal cavity include viral infections and nasal cavity cancer.

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