How do we actually smell?
For many mammals, a strong sense of smell is essential for survival. Most mammals rely on their noses to detect environmental hazards, identify food to eat, or locate prey. While human smell is no longer important from an evolutionary perspective, we still need to rely on our sense of smell to sniff out bad food or environmental hazards like fire and gas. This enables us to distinguish between 10,000 smells. And how exactly does smell work in humans?
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In our nasal mucosa, in the region of the roof of the nose, there is a special area that is equipped with special olfactory cells. This area is called the olfactory mucosa and has around 10 million olfactory cells. Olfactory cells are nerve cells that absorb odors from the environment via delicate sniffing hairs. Once an odor molecule has bound to a suitable receptor on a sniffing hair of an olfactory cell, the olfactory cell releases a special electrical signal. This signal is transmitted directly to the brain via the olfactory nerves, where it is processed and interpreted in the olfactory bulb, a small bulge in the frontal base of the brain.
Our ability to smell therefore largely depends on the error-free function of the olfactory cells and olfactory nerves. However, if these cells are dysfunctional, our olfactory system can fail completely. These causes can cost us our sense of smell.
These 3 causes can trigger anosmia
Viral respiratory infections
One of the most common causes of transient anosmia is respiratory infections. Even a simple cold can impair the olfactory cells in the roof of the nose so much that signals are no longer sent to the brain. In addition, when you have a cold, the mucous membranes in your nose swell. It is difficult for us to breathe because the narrow nasal airways are blocked. If fresh air no longer reaches the olfactory cells, they can of course not pass on any olfactory information.
Loss of smell is particularly common with COVID-19 infection. Anosmia is now considered one of the leading symptoms of the disease. The viruses cause severe inflammation of the olfactory cells and supporting cells in the roof of the nose. Sometimes the cells die and are not regenerated. Then the severe limitation of the sense of smell or the complete loss of smell is sometimes permanent.
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In diseases of the central nervous system, nerve cells in the brain die. In addition to effects on the motor function of the muscles, one of the more common symptoms of the disease is a reduced sense of smell up to the complete loss of smell. Indeed found researchersthat the loss of the sense of smell in many Parkinson’s sufferers occurred years before the typical symptoms of the disease. Upon closer examination, it was found that the olfactory bulb in the brain of people affected by the neurological disorder was only about half the size of people who did not have Parkinson’s disease.
Nasal polyps are benign growths of the nasal mucosa. They grow out of the mucosa in the turbinates in the form of droplets and are connected to the mucosa by a tissue stalk. Depending on how large a polyp becomes or how many such polyps grow in the paranasal sinuses, nasal breathing can be severely restricted. Less fresh air at the olfactory cells then also means the loss of the sense of smell. Nasal polyps also often cause headaches and a feeling of pressure in the midface.
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