The nose and the brain work together to detect smells. Olfaction, the sense of smell, is the process of detecting and processing chemicals present in the air. When these chemicals enter the nose, the olfactory system takes over to process them. Sometimes a fragrance may be enjoyable, such as perfume or the smell of cookies baking in the oven. The olfactory system also processes undesirable scents in conjunction with the brain. The sense of smell is the only one of the five senses that delivers immediate responses with instantaneous recognition and response.
As vaporized odor molecules enter and travel up the nostrils, they dissolve in mucous present in the nose. The olfactory epithelium lies under the mucous. This membrane contains special receptor cells that react to various chemicals. As the receptors react, they detect smells. The receptors are able to detect many different odors before transmitting a message to the olfactory bulb, with sits at the rear of the nose. From this point, chemicals move along to mitral cells located in the olfactory bulb. Special signals move to the brain for processing chemical smells.
The brain has the fascinating capability of memorizing and recalling smells. The brain can even perform this feat years after smelling a specific scent. The destination of chemicals in the brain depends on the kind of molecules. Some chemicals move to the limbic system, which is responsible for memories and emotions. Other chemicals move to the neo-cortex, which involves conscious thought processes. As the brain processes scents, it accesses connections between specific smells and memories. This is why a scent can conjure up a memory of an event, place, time, or person.
The limbic system sits in the center of the brain, and it has a direct connection with the central nervous system. When odor molecules arrive at the limbic system, the system processes them regarding their connection to memories, motivation, and emotions. The limbic system is instinctive, so the reactions stemming from this area of the brain are not a result of conscious thought. When chemicals move to the neo-cortex, they arrive at the thinking section of the brain. This area of the brain is responsible for translating smells. The way the cortex processes a chemical determines what happens next. If the smell has a positive association, it might be passed to the limbic system for further appropriate response. If the smell has a negative association, such as a connection with a bad experience, it might move to the endocrine system to facilitate a fast physiological response.
Taste is known as "gustation." The senses of smell and taste are intertwined, and taste relays on smell for processing. Chewing food involves the vaporization of odor molecules, moving up from the back of the mouth and into the nose. As the olfactory system of the nose processes the odor molecules, the sense of taste gets needed data to process the foods, too. This connection between taste and smell is the reason that people lose their sense of taste during a cold. Excessive mucous present in the nose prevents odor molecules from reaching olfactory receptor cells.
Humans can detect and differentiate between about 10,000 different smells, but categorizing and identifying this huge array of scents can be difficult. Some people have special training that enables them to identify scents. Perfume experts, for example, are trained professionals with the ability to remember and identify a large number of scents. Smelling nice is a priority in many areas of today's society. However, different cultures have different ideas about what constitutes pleasant and unpleasant smells. Creating a designer fragrance involves the study of both chemistry and psychology to design a mixture that people will enjoy.