We explain what the sense of smell is, what it is for, how it works and how to take care of it. Also, what are olfactory receptors?
What is smell?
One of the five senses with which human beings and many animals can perceive the surrounding reality is called smell or sense of smell. In this case, it is the ability to detect particles and traces of chemicals in the air, using receptors in the nasal cavity (that is, the nose).
Smell is a very common ability in nature, so much so that it is the primary sense of many animal species. However, in the case of invertebrates and amphibians it is more diffuse and less recognizable, since these animals have the ability to perceive chemicals in the environment through their skin and other organs very different from the nose of higher vertebrates.
In any case, through smell we perceive odors: particles that are released from matter and remain in the air, from where they are taken during breathing by specialized nerve receptors in the nose.
In the case of human beings, it is a poorly cultivated sense, in relation to sight and hearing, but no less important, since it connects much more quickly with our memory. It is estimated that we can recognize around 10,000 different smells on average throughout our lives, distinguishing between pleasant and unpleasant, pleasant and stimulating ones.
What is the use of smell?
The sense of smell is of critical importance for living beings, since allows you to recognize the matter without coming into direct contact with it and even having no idea it's there.
Being a passive sense, requiring little concentration, It is a continuous source of information respect to the environment, revealing the presence of smoke or strange odors that may alert of a threat. In addition, smell allows us to identify familiar environments (which is precisely why animals “mark” with their smell) and to notice the state and composition of the food before eating it.
How does smell work?
The smell is the interaction between odor molecules (that is, with odor) present in the atmosphere and specialized receptors present in the nasal mucosa, neurons capable of transforming chemical information into electrical impulses that are transmitted to the brain.
For this to occur, the air loaded with odorous particles must be inhaled and come into contact with the olfactory mucosa that lines the inside of the nose. There, the olfactory sensory cells (around 20 or 30 million on average) capture these chemical traces and transport them through their cilia (filaments) and fixing proteins present in the mucus, so that they can meet the specialized neuroreceptors.
The nervous information from these neurons penetrates the skull through micro-holes in the cribriform plate of the ethmoid bone, and in the anterior region of the brain they reach the olfactory or olfactory bulb, a neural structure of the forebrain that recognizes information and transmits it to the higher areas of the brain, where it enters conscious thought.
Smell is a sense very similar to taste, since both consist of chemoreception, but while the first is at a distance, the second is through direct contact with matter. Both stimuli, in fact, are processed in the flavor and taste center in the middle part of the frontal lobe, that is, in the same region of the brain.
Olfactory receptors
The olfactory receptors are responsible for converting the chemical information of the smell into nervous information. They are found in the mucosa of the nasal cavity, distributed in two clearly differentiated regions:
- The red pituitary with a large presence of blood vessels but without olfactory functions, which heats the inhaled air and filters it of impurities and particles.
- The yellow pituitary where the olfactory cells that contain the smell receptors are found.
Smell receptors are many and very specialized, especially in mammals. It is thought that there may be up to 1,000 different receptors, so the proteins responsible for odor processing occupy a good portion of the genome.
Each of the specialized receptors recognizes a different type of odor so the so-called “primary smells” (which make up other more complex aromas) are many and difficult to define.
Even so, it is estimated that the odors available to humans can be classified into 10 different lines: fragrant or floral, woody or resinous, chemical, citrus, non-citrus fruity, menthol, sweet, smoky or burnt, rotten and acrid or rancid.
Smell care
Taking care of the olfactory sense is reduced to taking care of the nose itself and its internal components. To do this, it is advisable to comply with the following recommendations:
- Keep your nasal passages regularly clean by blowing but without putting excessive pressure on the nose.
- Do not introduce objects into the nasal cavity much less those that can hurt it, change its chemical constitution or that can lodge inside.
- Avoid smoking cigarettes and similar substances, as well as aerosols with a very intense odor.
- Do not expose yourself to high concentrations of humidity dust or strong-smelling substances for a long time.
Continue with: Sense of touch
References
- “Smell” on Wikipedia.
- “How does smell work?” (video) in Smile and Learn Spanish.
- “Physiology of smell” in Access Medicina.
- “The powerful sense of smell” at Texas School for the Blind and Visually Impaired (United States).
- “Smell (sense)” in The Encyclopaedia Britannica.
