How does the smell spread?
From fragrance molecule to smell
The human olfactory cells have 350 different types of receptors that are randomly distributed over the entire olfactory mucosa. Each of the receptors only responds to a very specific fragrance molecule (odorant). When a scent molecule docks onto its specific receptor, it triggers a cascade of reactions in the associated olfactory cell: the binding leads to the formation of an electrical signal, known as an action potential. It is used in conjunction with countless other action potentials along the nerve cell extensions (axons) of the olfactory cells Olfactory bulb (Olfactory bulb) forwarded. Here between 1,000 and 2,000 clusters of cells (glomeruli) sort the action potentials according to their origin. Because in each of the many glomeruli only the axons of olfactory cells with the same receptor types end. In this way, the signals from the same scents can be taken together and transmitted together to a nerve cell in the olfactory tract. Bundled in this way, the action potentials reach the cerebrum and the so-called olfactory cortex. This "center of perception" combines them into a smell that finally reaches our consciousness.
Odors now consist of many different odorants - the scent of freshly ground coffee, for example, has more than 650. This explains why numerous olfactory cells are activated at the same time with every smell perception and generate electrical signals. Every smell leads to very characteristic nerve reactions. If you combine the action potentials of the 350 different types of receptors, you get a remarkable number of around 10,000 smells that we can differentiate.
Vomeronasal organ: the "sixth sense organ"
In the lower front part of the nasal septum, about 1.5 cm away from the nostrils, a thin, blind-ended tube can be seen when looking through the microscope: the so-called vomeronasal organ, or VNO for short. Its job is to receive sexual fragrances, the pheromones. As electron microscopic examinations of the nasal mucous membrane have shown, the received pheromones are passed on via direct nerve connections in the brain to the hypothalamus and the limbic system. Once there, the erotic impulses are processed and sexual activity is stimulated.
Like numerous other animals, humans also send chemical signal substances, the so-called pheromones. They serve as sexual attractants and are released from puberty through sweat, especially from the armpits and genital area. The signal substances trigger different vegetative, nervous and hormonal reactions - without being aware of the stimulus.
Over 50 pheromones have been discovered in humans so far. Among other things, the copulins in the secretion of the vagina and the androstenones in male sweat. Copulins stimulate the male libido, while androstenones promote female willingness to have sex: In one study, significantly more women than men sit on chairs in a waiting room sprayed with them. Further research showed that androstenones improve mood and increase physical arousal in women.
The pheromones also include the testosterone derivative AND and the steroid EST, which is similar to estrogen. The former was found in men's sweat, among other things, and the latter in women's urine. Scientists from the Karolinska Institute in Stockholm were able to show that the two substances represent something like an "identifier" for possible sexual partners: If women smell AND, this leads to the activation of the anterior hypothalamus, which, among other things, controls sexual activity. On the other hand, if you hold EST under your nose, the nerve cells in the hypothalamus are silent. With men it is exactly the opposite: they respond to EST, but not to AND.
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