To better understand how much information we receive from our sense of smell, it will serve us to better understand the mechanics of how the nose functions. The nose comprises two large chambers, separated by the septum. At the top of these chambers are millions of olfactory epithelia where smells are detected. These cells, in turn, send electrical signals to the hypothalamus centered in our brain stem. This area of the brain registers emotions such as anxiety, fear, and aggression as well as bodily functions such as appetite, metabolism, and sex drive. With smell, it is not just the olfactory receptors that are involved as they are bathed in mucous which contain odorant—binding proteins (OBPS) that bring odors to the appropriate receptors that convert them to impulses that impinge on our brain.
Olfactory bulb and nerves
The nose is comprised of two systems: the main olfactory system (MOS), which is how we identify food odors, and the vomeronasal system (VOS), which detects sexual odors or pheromones, smells that are generated by hormones to inﬂuence our sexuality. The main olfactory receptors (MOS) contain an estimated ﬁve million cells embedded in nasal mucous. The MOS utilizes cilia in their receptor cells (fine hairs) that distinguish odors such as food.
Independent of the MOS is the vomeronasal organ system (VOS) in which, the vomeronasal organ (VNO) is the center. Also known as Jacobson’s Organ, it is located inside the upper pole of our nasal bridge and detects pheromones and ferries this information to the limbic brain (the non- thinking, primitive brain), where sexual attraction and the ﬂight and ﬁght responses are stimulated. The VNO differs from the MOS in that its innervation is distributed via distinct channels on each side of our nasal bridge and have special neural receptors which have microvilli, small projections from their cell surface that are distinct from the hair-like cilia receptors found in the MOS. These microvilli respond to sexually derived odors that interact with our brain stem and frontal cortex.
The exact centers for human sexual response in adults have not been defined except as measured by heightened brain wave patterns that are stimulated beyond conscious awareness as defined by sexual smell (pheromones) as distinct from odors involving food. The VOS in some way must make contact with our limbic, primitive brain that helps us to respond to our social environment. To be “limbic” is to be youthful and the “limbic look” is what you see in the eyes of lovers or two- or three-year-olds, delighted by the discovery of love or their ability to explore their environment.
The Jacobson’s organ, the key receptor of the vomeronasal system (VOS), contains distinct non-ciliated micro-villous receptors independent of the olfactory nerve. These go to the brain via a separate accessory nerve to a distinct brain nucleus in the amygdala, a part of the limbic center of the brain (Scalia & Winans, 1976) which also involves broader areas in the human brain. Debate continues in the medical and scientiﬁc communities as to whether Jacobson‘s organ, the vomeronasal organ (VNO), is truly amazing.
The functioning or if it’s a vestigial organ in human beings that is only active in the human embryo. To further complicate matters, there are experts who say that pheromonal communication, or the awareness of sexual odors, can occur in the absence of a functioning Jacobson’s organ. Essentially, the debate centers on how one defines pheromones and pheromonal communication. We will argue that pheromonal communication is made possible by the vomeronasal organ and in humans it still may play a role almost as vital as that seen in the sexual responses of our mammalian friends: cats, dogs, and horses, where the VNO and its VOS connections are more clearly deﬁned, and sexual behavior is outrightly governed by their noses.
First identified by Danish scientist Ludwig Levin Jacobson in 1811, the vomeronasal organ, or Jacobson’s organ as it is called, was believed to be a non-functioning organ in humans. However, in the last decade studies have been conducted that strongly suggest that nearly all healthy people have a vomeronasal organ. At the Univ. of Colorado Medical School in Denver in 1991, Bruce Jafek, an ear, nose, throat surgeon and David Moran, a cell biologist and electron microscopist, examined 200 people and discovered that all of them except two had a vomeronasal organ.
In another study at the Univ. of Mexico Medical School, a thousand patients who were seeking plastic surgery were examined, and of that number, in 808, the vomeronasal organ was easily detected. Among the others, 125 patients had deformities of the nasal septum that, once corrected, enabled the doctors to see the vomeronasal organ in all but 23 patients. Jose Garcia-Velasco concluded in this survey, that the vomeronasal organ is “a normal, distinct structure of the human nose, and is present in practically all subjects studied.” Again, the vomeronasal organ, although it anatomically shares its place in the nose, is structurally different from our more familiar main olfactory system (MOS) that detects food odors. Both the vomeronasal and main olfactory systems touch related areas of the brain, but their functions are distinctly different. In that regard our sense of smell is engineered by a cluster of cranial nerves, including the vomeronasal (VOS); the main olfactory nerve and its olfactory bulb (MOS); and the trigeminal nerve.
Anatomically, in addition to the more widely recognized VOS and the MOS, we are now beginning to recognize the importance of a fourth distinct olfactory pathway. This is the “terminal nerve” (nervus terminalis) which. was first described in sharks. This nerve is responsible for sexual behavior, governed by the release of lutenizing releasing hormone (LHRH) from the brain. LHRII governs ovulation and/or sperm production in humans. Hormones, which interfere with LHRH, are currently being used to stimulate or control fertility and, when blocked, to treat prostate cancer in men and precocious puberty in children. LHRH releases the lutenizing hormone (LH) that governs sperm and egg formation. The developing YNO exports LHRH to the brain hypothalamus from its developing site in the embryo’s nose. Responses to these gonadotrophic hormones increase with sexual maturity and with the onset of menopause in aging women and andropause in aging men decrease. In regard to the above, the terminal nerve is also an odor receptor, but its functional presence in mammals 1S still open to question.
The trigeminal nerve responds to severe olfactory stimuli, such as spirits o ammonia. There are more cranial nerves, central nerves governing the sensory input of our head and brain involved in smell perception than any other communication system. Smell, which inﬂuences taste, represents a fundamental survival system going back to the origins of life.
Mcciiran discusses the anatomy and physiology of the VNO and the VOS, aln its related controversy, in a paper asking “Are the Surviving homtlegonasal Pits Connected to Responsive Brain Centers in the Adult respond to Odor? There.is evidence that there is an electrical . rain response to chemically active stimulants called “vomerophorins” in adults. The absence of a well deﬁned brain center as has been seen in other animals, these investigators feel reflects on the major evolutionary expansion and adult growth of the human brain where this auxiliary olfactory center, involved in sexual communication, is diffusely hidden, but still functional.