Vision is the dominant system that is connected to area 17 of the cortex and the Parietal area, but we are going to focus on the smell areas because it is also important for survival. It warns us of hazardous substances in our environment and further the sense of smell and taste are closely linked.
Detecting smell is detecting a chemical sense. Specialized receptors in the nasal cavity detect incoming molecules, which enter the nose, which enter the nose on air-currents, and they bind to receptor cells. Sniffing sucks up more odor molecules into the nose allowing you to sample a smell. It is a reflex action that occurs, when a smell catches your attention and helps warn you of danger such as smoke from a fire, or rotting food. Olfactory receptors located high up in the nasal cavity send electrical impulses to the Olfactory bulb in the limbic area of the brain for processing.
Smell Pathways
Odors are initially registered by receptor cells in the nasal cavity. These send electrical impulses along dedicated pathways to the olfactory bulb (each nostril is attached to one olfactory bulb). The Olfactory bulb is is part of the brain’s limbic system, the SEAT OF OUR EMOTIONS, DESIRES, AND INSTINCTS, which is why smell can trigger strong emotional reactions. Once processed by the Olfactory bulb, data is transmitted via three Olfactory pathways to higher centers in the brain that processes data in different ways. This process is called “orthonasal,” a process in which smell data travels along pathways directly from the nose. (a baking loaf of bread comes to mind…yum). In “retro-nasal” smelling odors also have a flavor component that enters the olfactory pathway via the mouth.
Receptor Arrays are about a 1000 types of receptor cells in the nasal cavity, but we can distinguish around 20,000 different smells, so clearly there is more to smell receptors that one receptor and one smell. Research shows that each receptor has zones on it which respond to a number of smell molecules and it may be that each receptor binds to a different pathway, or a specific smell will activate a different pattern, or array across the receptors, so that each smell has its own signature.When the receptors forming activate a specific pattern this signature is sent to the brain for processing.
The Chemistry of Smell has a lot of learning to be done in research about the relationship of chemical structure and smell. (For example, synthetic hair dye effecting the brain is an area of research I have written about, and it is not just smells, but the synthetic compounded organic chemicals that are causing cancers, and effecting our systems, such as Artificial Turf grasses, and our Ozone layer, and our carbon bonds). Scientists have identified 8 primary odors (like the the three primary colors for vision) these are camphorous, fishy, malty, minty, musty, spermatic, sweaty and urinous. Smells are often produced by a combination of many different smell molecules, often from different categories, have shown some similarities for example minty smelling compounds that share a similar molecule structure. Tiny differences in molecular structures can produce very different smells. Octonol a fatty alcohol. smells like oranges, while octonol acid, a saturated fatty acid that differs by only one oxygen atom, smells like sweat. (The smells of two molecular structures which are two molecules, can both conjure the same characteristic smell (mothball smell of camphor), because they share a common structural feature that has the same odorant property when picked up by olfactory receptor cells).
Side note…..Scientific research on perception of smell have attempted to identify primary odors which can be combined with one another to produce the much larger range if smells that we experience. 8 primary odors have been identified and one of those being the distinctive smell of fish. From my perspective as a researcher, I can smell odors from Stress related smells, to nickle smells in the body under stress, and water smells have a element of ores to it, and marijuana anywhere near me in second hand smoke, starts a pattern of my left leg vibrating. So smells do effect us and tell us when in danger of a group of combined smells, or compounded chemistry that synthetics, and that could be dangerous to our particular makeup in DNA. My sensitivity to my own senses, has saved my body many times over my life. Being hyper aware of your environment in many ways, can be quite life serving. It is my perception to never close yourself down to your own bodies reactions to environment and those around you.
Olfactory Epithelium
There are within each nasal cavity that contain the olfactory receptor cells is known as the Olfactory Epithelium. A small amount of the air entering the nostril will pass over the epithelium which is covered in mucus. Smell molecules in the air dissolve in the mucus bringing receptors into direct contact with the smell molecules. Three cell types are within the epithelium in addition to receptor cells and some are supporting cells which supply a constant supply of mucus, along with basal cells which produce new receptor cells every few weeks. The larger the epithelium the keener the sense of smell. Dogs as an example have a much larger epithelium that homo sapiens do. The receptor cells detect odors and danger and relay data along nerve fibers to the Olfactory bulb, which is part of the limbic system related to emotions, desires and instincts. Signals from the Olfactory bulb travel along the olfactory tract to the Olfactory cortex. The amygdala receives a signal from the Olfactory cortex if the molecules spell danger, generating emotions of fear, Orthonasal smell pathways referring to olfactory data system is stimulated by floral, perfumes, smoke, food aromas, social odors, the smell of prey, and the smell of pheromones and process signals alert the Orbit-frontal cortex, and if you really understand the process, in the case of a sneeze of a man made group of sequentia called Covid 19, that invaded our Orbito-nasal system, it would notify the immune system to protect our survival by adapting the systems, but the immune system over reacted. The anti bodies fighting off this particular group of antigens , along with the vaccine;s efficacy, was unable to keep up to this particular Covid 19 virus. Research by Dr. Hansen showed the particles of Covid 19 to go as far as 27 feet, leading to mask wearing being advantageous during this Endemic of November, 2019 from Wuhan China Lab. I had a reason for being concerned of a biological virus. because the Olfactory system is vital for our survival.
Carolyn D Hogarth this day of March 21, 2023..my observations.
