How does the sense of smell work in humans?

How does the sense of smell work in humans?
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The sense of smell allows us to perceive taste much better. This sense is less acute in humans than in other animals, but it is nevertheless an important one. It can help us distinguish between tastes, but it can also alert us to dangers such as noxious fumes.

How does the sense of smell work?

To understand how the sense of smell works, it is necessary to look at exactly what smell is. It is also called odorous substances – volatile compounds that enter the nasal cavity along with the air. You cannot see the odor because odor molecules are elusive to the human eye. As they travel to the nostrils, they mix with the air.

When inhaled, these invisible elements are placed on the olfactory epithelium that lining the nasal cavity. It is located within it on each side and occupies an area of about 2.5 cm 2.

Although this area is very small, there are an enormous number of receptors on its surface – it is estimated that there may be as many as 50 million of them. In the olfactory field, there are several types of cells – supporting, bipolar and basal.

The receptors responsible for “picking up” odors are the bipolar cells. They contain about a dozen cilia immersed in the mucus covering the epithelium. Odorous substances that reach the cilia quickly dissolve in it. This process is extremely important because the mucus contains a protein that binds odorants – this is OBP. Its job is to transport odorant molecules that enter the nose.

Bipolar cells – as the name suggests – have two poles. The second one releases so-called axon spears, which form the olfactory threads. These, in turn, head to more cells that direct odor information to the olfactory centers, located within the hippocampal bend, the cerebral cortex, and the amygdala. It is the brain that processes the information delivered to it and assigns meaning to a given odor. Interestingly, each smell can be associated differently by a person. Some people associate the smell of oil with fried pork chops, while others associate it with French fries.

Perception of smell is therefore an individual thing, and not every smell will evoke the same associations for all people. It is thought that an average person can identify around 10,000 odors.

Photo: Drobot Dean/Adobe Stock

What functions does smell have?

Since the dawn of time the sense of smell had a protective function – it was to help us identify danger and give a signal to escape. As time passed, the number of threats decreased, and the sense of smell began to have other functions.

It is mainly used during the meal: if a food smells good, we are more inclined to eat it. Importantly, the sense of smell regulates the production of saliva and gastric juice, which is why grocery stores have introduced, among other things, baking bread on site. With a pleasant smell, customers are tempted to buy fresh rolls or sweet pastries.

The sense of smell is important from birth – a newborn baby can smell its mother. Many pediatricians and neonatologists recommend kangaroo care, i.e. skin-to-skin contact. This way the baby feels safe, not only feels the warmth of our body, but also the scent of our skin.

Smell regulates our sexual activity – the smell of pheromones and perfumes pleasant to the nostrils encourages sexual intercourse. Some scents mobilize intellectual effort or relax the body before sleep.

Why do some people have a heightened sense of smell?

Some people may have a very sharpened sense of smell. This is because they have many more receptors in their nostrils than the average person. Some medications, as well as drugs, can also sharpen this sense. Pregnant women also have a heightened sense of smell, as hormonal changes can completely reverse the sense of smell. Those associated before pregnancy with pleasant memories can become unpleasant during pregnancy.

Photo: Antonioguillem/Adobe Stock

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