What makes smell in the air

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totally phenomenal - senses

The outer walls of the nose are visible, but the essentials are hidden inside. The nostrils form the entrances to the two nasal cavities, which are separated from each other on the inside by a cartilaginous wall, the nasal septum. Since the nose consists of two cavities, it is called a paired olfactory organ. At the bottom, the palate plate separates the nose from the oral cavity.

At the back of the nose there are two more "inner" nostrils (chonanas). Through it, the nose is in direct contact with the throat. This opening between the mouth and nasal cavity is responsible for the fact that a drink runs out of our nose when we cough if we swallow hard while drinking.

  • Cut parallel to the face. You can see eye sockets, turbinates, sinuses and the oral cavity.

From the nasal walls three bulges, the turbinates, protrude into the nasal cavity, which, depending on their location, are called the upper, middle or lower turbinate. They are covered with a mucous membrane whose cilia and mucus keep the nose clean. They ensure that dirt and bacteria are removed. The fine hairs in the nostrils help you with this task: They filter the air you breathe when you breathe in and don't even let coarse dirt in.

Above the upper turbinate, very close to the brain, lies the olfactory region, an olfactory mucous membrane with millions of olfactory cells that are responsible for the actual olfactory ability of the human nose. This mucous membrane has an area the size of one or two postage stamps. This is where the five to six million olfactory cells that enable the olfactory process are located.

Olfactory cells and smelling

A fragrance is a chemical substance, so it consists of Molecules. But how does a molecule become a nerve stimulus? That is the question that scientists have been grappling with for a long time. It is only in the last twenty years that they have come closer to the answer.

For the actual olfactory ability of the human nose there are millions of Olfactory cells (= olfactory cells) responsible, which lie in the upper part of the nasal cavity.

The human olfactory region

In order for the "smelling" process to take place, the olfactory cells must recognize the odor molecules in the air and ensure that their odor information reaches the brain. How does this work? Scientists put it this way: "Smelling is one chemoelectric transduction". That means: When you smell a chemical signal is converted into an electrical signal Olfactory cells are the Interpreterwho speak both languages: They master the chemical language of the odor molecules in the air they breathe and translate the odor information into the electrical language of the brain. So olfactory cells are nerve cells, because the essence of nerve cells is that they take in information from the environment and in electrical signals convert.

  • The human nose

On the side that comes into contact with the air you breathe, an olfactory cell has many thin olfactory hairs that are covered with mucus. These hairs are also called Cilia. The odor receptors, which represent a kind of "landing stage" for odor molecules, lie on them.

If a scent molecule gets into the nose with the air we breathe, it dissolves in the mucus and can then attach to the olfactory receptor. This docking triggers an electrical impulse in the cell. In other words: the odor information is translated from "chemical" into "electrical" language.

A single olfactory molecule is not enough to generate an electrical stimulus in the olfactory cells. An odor sensation only occurs when there are enough fragrance molecules in the air we breathe and can also bind to the olfactory cells. If enough odor molecules bind, an electrical voltage is created that amplifies the olfactory cell inside by a factor of 1000. This electrical message is then passed on to the brain and ultimately causes the sensation there.

Olfactory receptors

Each olfactory cell carries numerous olfactory receptors, the docking points for olfactory molecules, on the cilia. These receptors consist of proteins and, depending on the type, can bind certain molecules to themselves.

Representation of an odor receptor

All docking points of a certain cell have the same structure, which means that they only fit one type of scent molecule. In humans there are around 350 different olfactory receptors and thus also 350 different olfactory cell types.

However, fragrances consist of many different fragrance components. Natural rose scent, for example, is made up of over 500 different fragrance components. In order for the brain to perceive a complex scent, it must many olfactory cellsthat carry different odor receptors work together.

The different odor receptors are linked to one another.

If one compares smelling with "translating", each olfactory cell type corresponds to a letter in the dictionary of smells; To understand a scent note, many different olfactory cells have to work together to form a familiar word or message for the recipient.

Since humans have fewer different types of olfactory cells than the components of the rose scent alone, suggests that the human sense of smell is very limited. A dog, for example, has many more different types of olfactory cells.

From the nose to the brain

The electrical stimulus that arises in the olfactory cells when a fragrance is bound is transmitted via a long, thin cell extension, the Axon, forwarded.

The axons of olfactory cells of the same type (which can perceive the same substance) bundle together to form olfactory fibers, which then pull into the brain - perhaps comparable to a power line. This lies directly above the olfactory region of the nasal cavity Ethmoid, a plate of bone that separates the nose from the brain. The ethmoid owes its name to the many needle-point-sized holes that give it the appearance of a sieve. The olfactory nerve fibers pull through these holes into the Olfactory bulb, the first "smell station" in the brain. This Olfactory bulb - that's what experts call it - lies directly above the bridge of the nose.