Sunday, December 2, 2012

NOSE

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NOSE
Nose, organ of smell, and also part of the apparatus of respiration and voice. Considered anatomically, it may be divided into an external portion—the visible projection portion, to which the term nose is popularly restricted—and an internal portion, consisting of two principal cavities, or nasal Fosse, separated from each other by a vertical septum, and subdivided by spongy or turbinated bones that project from the outer wall into three passages, or meat uses, with which various sinuses in the ethmoid, spheroid, frontal, and superior maxillary bones communicate by narrow apertures.
The margins of the nostrils are usually lined with a number of stiff hairs that project across the openings and serve to arrest the passage of foreign substances, such as dust and small insects, which might otherwise be drawn up with the current of air intended for respiration. The skeleton, or framework, of the nose is partly composed of the bones forming the top and sides of the bridge, and partly of cartilages. On either side are an upper lateral and a lower lateral cartilage, to the latter of which are attached three or four small cartilaginous plates, termed sesamoid cartilages. The cartilage of the septum separates the nostrils and, in association posterior with the perpendicular plate of the ethmoid and with the vomer, forms a complete partition between the right and left nasal Fosse.

SENSE OF SMELL
Smell, one of the five special senses by which odors are perceived. The nose, equipped with olfactory nerves, is the special organ of smell. The olfactory nerves also account for differing tastes of substances taken into the mouth, that is, most sensations that appear introspectively as tastes are really smells.
Sensations of smell are difficult to describe and classify, but useful categorizations have been made by noting the chemical elements of odorous substances. Research has pointed to the existence of seven primary odors—camphor like, musky, floral, pepper mint like, ethereal (dry-cleaning fluid, for example), pungent (vinegar like), and putrid—corresponding to the seven types of smell receptors in the olfactory-cell hairs. Olfactory research also indicates that substances with similar odors have molecules of similar shape. Recent studies suggest that the shape of an odor-causing chemical molecule determines the nature of the odor of that molecule or substance. These molecules are believed to combine with specific cells in the nose or with chemicals within those cells. This process is the first step in a series that continues with the transmission of impulses by the olfactory nerve and ends with the perception of odor by the brain.
 



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