The human nose has several physiologic functions. As the air is inspired through the nose it is humidified and warmed by passing over the moist and warm nasal mucosa. The nose is an energy-conscious organ in that expired air is cooled and some of the moisture is recaptured. The functions of warming and humidification require a tremendous blood flow to the nasal mucosa and also place substantial stress on the nasal mucosa. The nose has what is known as a nasal cycle.
To allow the mucosa time to rest from these functions, the nose has periods in which one side of the nose becomes swollen, which we call congestion. During the same period the other side of the nose remains patent or decongested. The normal nasal cycle lasts from three to six hours, and during this time first one side of the human nose will be congested and the other side will be patent; then the second side becomes congested as the first side becomes patent. It is also normal for the human nose to be congested when an individual lies down.
Particularly if you lie on your side you may notice that the downside of your nose becomes congested. Olfaction is the medical word for smell. Smell is one of the six human senses and for some individuals is a very important sense; for others it seems to be less important. The olfactory centers, as described under the anatomy section, reside very high along the roof of the nose. In order for these centers to be stimulated, the odors have to be inspired into the human nose and carried up to the roof of the human nose. If the odor does not reach the roof of the nose due to a variety of conditions, the odor will not be perceived. The nose is capable of distinguishing a large number of different odors. Our understanding of precisely how this occurs is limited, but increasing.
Taste is a sense very different from olfaction. It is another of the human senses and is perceived primarily on the tongue. There are four recognized tastes and these are sweet, salty, sour, and bitter. They occupy geographically separate areas on the tongue and are perceived in cells clustered together in taste buds. The sense of smell plays a major role in the flavor of foods and it is common for individuals who lose their sense of smell to report that food loses its taste. This is of course incorrect; the food has only lost its aroma, and taste (sweet, salty, sour, bitter) remains intact.