More than any other sensory experience, fragrances have the ability to trigger our emotions: to fill us with joy and rage, to bring us to tears and make our hearts ache, to incite us with terror, and to titillate our desires.
— Rachel Herz, The Scent of Desire

Olfaction: the action of smelling; the sense of smell. (Oxford) Sensory cells in the mucous membrane that lines the nasal cavity are stimulated by the presence of chemical particles dissolved in the mucus. (OxfordMed) The primary sense by which most of our animal brethren negotiate the world, including our primate relatives, and it is the sense to which they owe their survival. (Herz, 14) Processes the signals sent to the brain from our nose. (Doidge, 48) A unique feature is that it bypasses the “thalamus” (and connects) in the primary olfactory cortex. (Fisch, 382) Mediates the sense of smell. (Patestas, 241) Adjective - 'olfactory.' Editor’s note - also referred to as ‘olfactory system’ and “smell” and characterized by some authors as part of the limbic system. 

Olfactory Processes: implicated in the perception and transmission of olfactory sensation. Also believed to affect other neural systems associated with producing or influencing emotional, behavioral, and reflex responses. (These include) reflex responses such as reproductive and maternal behaviors, and visceral functions such as salivation, gastric secretion, and nausea. (Patestas, 336) Every day we inhale at least twenty-three thousand times. With each breath, air containing odor molecules, enters our nostrils and is swept upward into the nasal passages of the “nose.” The chemicals then make contact with the “olfactory receptors.” (Herz, 20) Imaging studies have demonstrated that the brain can respond to odors that are so faint we are not even conscious of smelling them. (Mathews, 52) ‘Anosmia” (loss of smell) can have a progressively negative downstream effect on the healthy functioning of our emotional system. (Herz, 8) The loss of the sense of smell brings with it severe disruption of mental health and happiness, while smell’s intact state brings texture, richness, and a brilliant emotional quality to life in innumerable ways. (Herz, 16)