The sense of smell also commonly referred to as olfaction is one of the most fundamental among the six senses that the human beings have. Throughout the evolution of the human beings, the sense of smell has played a significant part in survival because of the capability to distinguish a diverse range of odor. The sense of smell can evoke different emotions including those that are negative, positive and neutral (Patel & Pinto, 2014) . All the functions of smell are made possible by the effective structure of the olfactory system. It is important to realize that the sense of smell also has an impact on the human behavior. This study will delve into both the physiological aspects and the psychological aspects of the sense of smell.
Physiology of Smell (Structure and Function)
The human nose consists of an opening known as the nasal cavity. The roof of this cavity comprises sensory cells known as the olfactory receptor cells. There are small holes on the roof of the nasal cavity through which the olfactory receptor cells extend. These small holes that exist at the roof of the nasal cavity form a structure that resembles a sieve which is known as the cribriform plate. The olfactory receptor cells create the olfactory bulb which is located at the end of the olfactory nerve (Soudry et al., 2011) . The purpose of the olfactory bulb is to transport sensory information to the section of the brain which is responsible for interpreting and identifying a diverse range of scents.
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The structure observed in the nasal cavity is very useful in boosting the sense of smell of an individual. The walls of the nasal cavity comprise grooves known as the nasal conchae whose shapes enhance the circulation of the inhaled air around the nasal cavity (Patel & Pinto, 2014) . The nasal conchae are responsible for increasing the surface area of the tissues inside the nasal cavity that the inhaled air makes contact. The tissue in the nasal cavity is responsible for filtering and warming the air before it is transported to the lungs. Every time an individual detects an odor and sniffs it, there is an increase in the number of scent molecules. The molecules will be transported to the nasal cavity and into the sensory stimuli by the olfactory receptor cell. The odorant molecules must be able to interact with the mucus that overly the receptor cells. The molecules should be soluble in the mucus so that they can be able to reach the olfactory receptor cells (Soudry et al., 2011) .
The olfactory nerve is responsible for conveying the stimuli to the olfactory center which is located in the brain. The route between the olfactory nerve and the olfactory center is a direct route, and once the stimuli reach the brain, a person is able to detect the smell and react to it quickly (Walton & Maeso, 2012) . The brain is responsible for identifying the type of smell detected and providing a signal to the individual on how they should be able to react or respond to it. Some of the reactions that occur after an individual sniff at something are subconscious. For instance, the smell of chicken being baked in the oven could easily make the mouth of the person who smelled it to water.
Some of the other reactions are voluntary, for instance, the person smelling the baked chicken can decide to go into the kitchen and have the chicken. Also, the same subconscious and voluntary reactions can occur with bad smells. For instance, the smell of a sewer nearby could make an individual’s face to frown. However, the person can voluntarily decide to leave that area with the bad smell and go to a place where there is fresh air. Both the positive and the adverse reactions take place when an individual inhales a small number of molecules.
In most cases, smells are powerful stimuli which are responsible for different responses such as a sense of disgust or pleasure. In some cases, smells can be used to alarm an individual of a good thing that is about to happen or a dangerous thing. For instance, the smell of baked cake can alarm an individual of a celebration that is yet to take place. On the contrary, the smell of smoke could alarm a person of fire which can be quite dangerous in case there is an outbreak. Such sense of smell allows human beings to protect themselves from dangers, for instance, evacuate a building in case they smell acid which could be toxic to their health.
The sense of smell also influences other senses such as the sense of taste. These two senses have different sensors, however, 80 per cent of the time the sense of taste depends on the sense of smell (Soudry et al., 2011) . An individual will quickly identify if food is fresh or not through the sense of smell. At this point, they will decide to decide on whether they will taste the food or not.
Psychology of Smell
Psychologists in many studies have explained the relationship between smell and human behavior. Smell has been identified to have a strong correlation with human behavior. It is the very first warning of whether something is safe or dangerous. Smell has been attributed to many instinctive and subconscious reactions of human beings (Van Toller & Dodd, 2012) . Since time immemorial, human beings have been harnessing the power of smell so that they can be capable of utilizing it to their advantage in different situations.
In the contemporary world, many people judge others based on fragrances. In other words, fragrances have been attributed to the capability of influencing a negative or a positive psychological state of mind and affect the reaction of a person quickly. Positive smells like those of flowers have always triggered a calming state of mind and a sense of security (Van Toller & Dodd, 2012) . On the contrary, bad odors such as that of a dead human being have always lead to an instantaneous reflex to vacate the scene and seek help. In other words, positive smells allow people to behave in a friendly manner.
Smell has been linked to the capability to evoke emotions. For instance, the perfume industry operates under this concept of smell meaning that they create perfumes that tend to produce a diverse range of emotions and feelings like relaxation or even the desire for power (Walton & Maeso, 2012) . Also, psychologists have linked smell to the capability of individuals to choose their partners or be attracted to others. Research carried out shows that the body odor that is produced by people who have different genes can subconsciously help people to choose their partner (Van Toller & Dodd, 2012) . Scientists also link the act of kissing to smell because they believe that the action was first developed from sniffing.
The sense of smell aids people in remembering things from the past. Psychologists have termed this act “Proustian memory effect” meaning that scents can link people to their childhood memories (Van Toller & Dodd, 2012) . People can always trigger memories by smelling things that connect them to their past. For this reason, it can influence their behavior by reminding them of how good their past behavior was or how bad it was. In this sense, an individual can maintain their behavior or adjust it for the better. For instance, the smell of pancakes can make an adult remember how they used to have breakfast as a family in their childhood and therefore, continue this behavior with their new family after they get married.
In conclusion, the sense of smell is very crucial for our day to day activities. It helps human beings to survive by identifying safe environments and staying away from the dangerous ones. Also, it influences the behavior of the human beings, for instance, the selection of the life partners. The sense of smell is essential in evoking memories. It helps people to remember things that happened in the past which can be very beneficial in adjusting their current behaviors. Based on the study, it is essential to realize that the sense of smell has a significant role in safety, nutrition and the maintenance of the quality of life of an individual.
References
Patel, R. M., & Pinto, J. M. (2014). Olfaction: anatomy, physiology, and disease. Clinical anatomy , 27 (1), 54-60.
Soudry, Y., Lemogne, C., Malinvaud, D., Consoli, S. M., & Bonfils, P. (2011). Olfactory system and emotion: common substrates. European annals of otorhinolaryngology, head and neck diseases , 128 (1), 18-23.
Van Toller, S., & Dodd, G. H. (2012). Perfumery: the psychology and biology of fragrance . Springer Science & Business Media.
Walton, B., & Maeso, P. (2012). Can You Smell That? Anatomy and Physiology of Smell. Grand Rounds Presentation .
