How do we identify food based on smell
odor How scent gets from the nose to the brain
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Smelling is so normal for us that we usually only perceive the sense of smell when we lose it. Smells affect us more than we are aware. They affect memories and feelings.
To this day, nobody knows how many different smells we can perceive. It is easier to determine the performance of the senses in the eyes and ears than in the sense of smell. Because there are quantities that serve as a reference: the spectrum of the wavelengths of light visible to humans and the audible sound frequencies. It is estimated that our hearing can recognize around 340,000 different sounds. Eyes can distinguish between 2.3 and 7.5 million colors.
The sense of smell is difficult to measure
There are hardly any reliable numbers for the sense of smell. Since it is not known how many odor molecules there are in total, it is also not known how many of them the human nose can recognize.
In 2014, researchers from Rockefeller University in New York announced that the human nose can distinguish a trillion smells. This study result has since been refuted. A calculation error had crept into the statistical extrapolation based on experiments. Since then, the following applies again: You don't know how many smells a person can distinguish.
Smells - in the fast lane to the brain
What we do know, however, is that the sense of smell is the only sense that has direct access to the center of memory and emotions in the brain, i.e. to the hippocampus and the limbic system. The sense of smell is also the oldest sense that is already formed in the womb: smelling, says olfactory researcher Hanns Hatt from the University of Bochum, developed in evolution before seeing and hearing and was of elementary importance even in the "primeval sea".
Follow your nose - communication by smell
When the first living things went ashore - like lizards and crocodiles - they were able to communicate much further through their sense of smell than through sight. The smell not only made it possible to identify food or enemies over a long distance, but also suitable partners. This is why the sense of smell was so important in the first creatures on land and in all that evolved from them, Hatt continues. This development finally reached its peak in rodents: researchers know that mice and rats have the best sense of smell. While the primeval fish had ten olfactory receptors, rats have more than 1,000.
Smelling is shaped in the womb
Fragrances - like mother, like child
The sense of smell is also developed much earlier in human embryos than hearing and seeing. From the 26th to 27th week of pregnancy, according to Hanns Hatt, embryos show that the nose and the associated brain structures are already in place. And it has been proven that embryos can smell in the womb and thus get to know smells in the mother's womb. So it may be that later as a young person you have never smelled a scent yourself, but still reacts to it:
"We also learn to evaluate scents, with the mother, so to speak. So scents that the mother hates and that arouse particularly negative emotions in her are transferred to the embryo. And the embryo stores this scent as completely negative."
Professor Hanns Hatt, cell biologist and odor researcher at the Ruhr University Bochum in conversation with Gerda Kuhn, Bavaria 2
1991: Genes for smell discovered
How many smells we can smell is unknown. How the sense of smell works has been known in detail since 1991. The neurophysiologist Linda B. Buck and the physician Richard Axel from Columbia University, New York, discovered that there are olfactory receptor genes and also the first olfactory molecule. In doing so, the researchers discovered how the sense of smell is organized. Parts of the system were known in advance, for example signal cascades and messenger substances, but not the entire system.
In 2004, the scientists received the Nobel Prize for Medicine for their groundbreaking discovery. It has now been proven that humans have a total of around 800 olfactory receptor genes, half of which are switched off. So we only use around 400 of the odor genes that we have. Nevertheless, the olfactory receptor genes are still the largest family of genes in the human genome and make up around two percent of our genes.
The sense of smell is an open system
The sense of smell is a "dynamic gene pool", says Dietmar Krautwurst, olfactory researcher at the Leibniz Institute for Food Systems Biology at the Technical University of Munich (TUM). There is no "negative selection and mutations are allowed". This allows genes to be switched on and off. So further development is possible and room for evolution. That would be unthinkable in closed systems such as reproduction, the hormonal and central nervous systems. Mutations can have dramatic consequences here and the body switches to zero tolerance to be on the safe side.
Foods have "odor patterns"
The olfactory cells in our nose can perceive and process a myriad of volatile compounds in the air. And foods emit a variety of flavors too. They come from only 230 key flavorings that occur in different concentrations and mixing ratios in food. For example, butter only contains 3 flavorings, strawberries 12, red wine around 20 and whiskey 40. With the 230 key flavorings "you can put together almost any food," says Dietmar Krautwurst, who was involved in a study of odor patterns in food. It is interesting that humans have a similar number of active olfactory receptor genes in their noses, around 270 to 300.
When the nose wears off - cancer drugs, Alzheimer's, Covid-19
The sense of smell can be restricted due to mutations, but it can also be lost due to diseases. For example, in cancer and asthma patients through medication, through mental illnesses such as neuroses, viral infections, fine dust or toxic substances. Smell disorders can also be a warning signal and occur long before illnesses break out. This is known in neurodegenerative diseases such as Alzheimer's, multiple sclerosis and Parkinson's. The disturbance or loss of the sense of smell can be reversible as well as irreversible.
This is striking with Covid-19: An unmistakable symptom of the infection is the loss of smell and / or taste, even though you don't have a cold. According to one study, the majority of patients recovered within 28 days, but a quarter of those affected continued to struggle with limitations. One percent of the sick had not regained their olfactory ability after the infection. For some illnesses, odor training can be helpful, so that, according to Dietmar Krautwurst, "at least one can smell any odor again."
Odor receptors outside the nose
There are also olfactory receptors outside the nose, for example in the intestines, in the heart, in the lungs, in the testes, in the skin or in white blood cells, which are important for the work of the immune system. They are also found in cancer tissue. Their function in these places is still being researched. The sense of smell, our most archaic sense, remains exciting.
- There's something in the air! The world smells. odysso, ARD-alpha, 05.05.2020, 3.15 p.m.
- radioWissen: Supersensor nose - diagnosis and therapy of olfactory disorders, Bavaria 2, 23.03.2018, 09.05 a.m.
- radioWissen: Fragrances described - Always follow your nose, Bavaria 2, January 2nd, 2018, 9:05 am
- Planet Wissen "How smelling influences our life", with Prof. Hanns Hatt, ARD-alpha 07.07.2017, 3:00 pm
- IQ - science and research: "Smell - our oldest sense". Gerda Kuhn in conversation with the cell biologist and odor researcher Prof. Hanns Hatt, Bavaria 2, May 23, 2017 6:05 p.m.
- radioWissen: "Nose as a miracle - the human olfactory and respiratory organs", Bavaria 2, June 27, 2014, 9:05 am; July 10, 2014, 3:05 p.m.
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