The olfactory epithelium located in the nasal cavities of most vertebrates, for example, is endowed with cells specialized in the capture of odors of various types, even at very small concentrations.
There are two types of materials in the environment: those that give off particles (such as roses, perfumes, warm bread being baked in the oven) and others that do not (such as steel and glass). These particularities make us smell the roses, but not the glass.
|That's right: there are things that smell and some that don't. In atmospheric air, besides gases (oxygen, nitrogen, helium, carbon dioxide) there are numerous volatile particles, but not all of them stimulate the sense of smell (the sense of "smell"). We can feel around 2000 to 4000 different odors.|
The organ of olfaction is located inside the nose and captures the volatile chemicals of the inspired air.
When a particular smell catches our attention, we investigate it olfactorily, increasing the frequency of short breaths and dilating the nostrils.
How do olfactory cells detect odorants?
The eyelashes of the olfactory cells have receptor molecules specific to certain odorant molecules, and when they fit together, the sensory cell generates electrical impulses (or nerve impulses). The nervous signal is sent to the brain, where finally interpretation occurs. The specificity between the receptor and odorant molecule is such that the molecule d-carvona evokes the scent of caraway seed (a type of Arab cumin) but if it is modified to l-carvonawill evoke the smell of mint!
How do nerve impulses get to the brain?
Olfactory impulses travel through the olfactory nerve and reach the brain through the olfactory bulb. But it's in olfactory cortex that odorous information is interpreted by identifying the smell that has entered the nose. Sensory information is stored by the hippocampus to be remembered and are also sent to hypothalamus for organizing visceral functions (seeking food if it smells like food or nausea (craving) and even vomiting if it is carrion). Like all sensory experience, olfactory perception arouses emotional and behavioral experiences.
Olfactory experience varies from person to person and from concentration of the odor.
For example, John doesn't smell at all, and Mary can be extremely sensitive to a wide variety of odors. O hydrogen cyanide (gas used in the Nazi attempt to exterminate Jews during World War II) is a powerful poison: one in 10 people can not feel it. That is, there are people with anosmia (olfactory deficit) for a given group of substances as color-blind people. In addition, for each odorant group the sensitivity depends on the chemical concentration: to feel the ethyl ether, A concentration of 5.8 mg / liter is required but for methyl mercaptan only 0.5 ng / liter is enough. This substance is added to the cooking gas to detect any leakage!
Fruits and flowers produce esters that evoke their typical smells. By smelling a ripe banana, your olfactory epithelium will be decoding the isoamyl acetate! And if it smells like an orange, the ester octyl acetate! The chemical industry produces several flavoring (artificial flavors) which are added in the constitution of processed foods in order to stimulate the consumer's sense of smell and taste.
Why don't we smell things when we have a cold?
You may have already had a cold with a 'stuffy' nose and have noticed that you are not feeling the smells and the taste of the food. This is because odorants do not reach the olfactory receptors because of the intense mucous secretion coming from the respiratory tract airways.
If it is not possible to transform the chemical stimulus into a sensory signal, the olfactory pathway cannot activate the olfactory cortex. In addition, when food is inside the mouth, volatile particles that reach the olfactory epithelium are released through the communication between the pharynx and the nasal cavity.
In other words, the taste of food depends not only on the taste but also on its aroma. When we are cold, the aroma of the food does not reach the olfactory epithelium, impairing the taste interpretation!