Olfactory System

The olfactory system is in charge of the sense of smell, aids in taste, and is involved with memory. Olfaction is the sense of smell, which is the detection of chemicals dissolved in the air. This body system involves the nose, nasal passages, and lining epithelial cells (some 50 million receptor cells in the human nose). These epithelial cells transfer odorant molecules in the air to the olfactory bulb, and eventually, to the brain, where they can be interpreted. The sense of smell is closely linked to the gustatory system, or sense of taste. In fact, the flavor in foods we consume is largely due to the sense of smell (about 95 percent), whereas a much smaller part of flavor in foods is conveyed by the sense of taste (about 5 percent). Because both sense of taste and smell are inextricably linked to the enjoyment of foods and beverages, they are also related to the development of obesity. Olfaction can drive hunger, particularly when one perceives a an aroma of a pleasurable food, such as fresh-baked cookies, or a meat on a barbeque grill. If either the biological systems that control smell or taste are damaged or function improperly, obesity can result.

The two main functions of the olfactory system are to distinguish one odor from another, and to make some judgment about the intensity or concentration of that odor. In addition to this function, the olfactory system also distinguishes “new odorants” that one comes across from background odors in the environment. Finally, an additional function of this system is to make connections between odors/aromas and memory, as the olfactory system innervates parts of the brain involved with this function. Indeed, olfaction and memory are linked—to what extent and in what chemical pathways are all still being elucidated in academic research. However, it is known that olfaction allows people to identify food, potential mates, predators, and provides both sensual pleasure, such as the smell of flowers, as well as warnings of danger such as spoiled food.

Olfaction is involved with obesity in that smell and taste are closely linked and what drives hunger and taste.

To accomplish all of these tasks, olfaction must first start with an odor. A chemical odorant must possess certain molecular properties to provide sensory information for the brain. The odorant must have water solubility, a sufficiently high vapor pressure, low polarity, and some ability to dissolve in fat and surface activity. These qualities are needed for the odorant to be dissolved in the air and for the olfactory system to detect it. The olfactory sense is able to distinguish among a potentially infinite number of chemical compounds.

The olfactory system involves the limbic system, amygdala, and cortex in the central nervous system (CNS). The amygdala is a small area in the brain that has two almond shaped sides with bundles of neurons located deep within the temporal lobes of the brain. Most research has shown that the amygdala processes memory and emotional reactions to life events and involve it with the limbic system. The limbic system is a set of structures throughout the brain that generate feelings, emotions, motivations, and help in learning and memory.

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