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Features of human perception. The sense of smell

In everyday life we perceive odors. They can be pleasant or unpleasant, these feelings can cause us anxiety and may even save a life. Odor perception plays an important role in terrestrial living organisms (hunt, search, pair, protection, etc.). This is more true for animals, but necessary and human. So, in addition to ordinary reactions, sometimes when we feel the familiar smell, our memory may have certain memories associated with it.

In this article we will try to understand the causes of these sensations.

Smell is a specific sense of presence in the air of volatile aromatic substances, detectable chemical olfactory receptors located in nasal cavity of animals and humans. This feeling is determined by the total effect of the irritation of olfactory receptors, receptors of the trigeminal nerve and receptors vomeronasal body; it's also possible that the sense of smell is involved in the perception of the aerosol component of the atmosphere. [1]

Thus, odor perception is the perception of the smallest particles of matter, organic and inorganic origin, with specific receptors.
Below we describe the physiology of smell perception.

Physiology of smell

When a person inhales, air flows through the nasal cavity to the lungs. However, during exhalation nasal airway partially overlap three bony outgrowths called nasal turbinates. When passing through them the air is mixed and lays smelling molecules to wet the mucosa. As a result, when the ordinary breathing we smell is stronger on the exhale than on the inhale. [3]

When you inhale through the nose the air, along with the molecules of odorous substances (called olfactory stimulus or odorant) is held in each of the two nasal cavities via slot-like channel complex configuration, which is formed by a longitudinal septum, and the three nasal turbinates. Here the air is cleaned of dust, moistened and heated.

Anatomy of the nose and throat. 1 – ostium of the auditory tube; 2 – pharyngeal tonsil; 3 – the main bosom; 4 – the main ostium of the sinus; 5 – zetoobraznoj plate of the ethmoid bone; 6 – frontal sinus; 7 – the top nasal Concha; 8 – middle nasal Concha; 9 – inferior nasal Concha; 10 – pristenok of the nose; 11 – solid sky. [5]

A portion of the air flows in the located in the upper rear area of the olfactory region, having the form of a slit, covered with olfactory epithelium. The epithelium is covered by a layer of olfactory mucus and contains three types of primary cells: olfactory receptors, supporting and basal cells. Air carrying the odorous molecules penetrate the nasal cavity and migrate over the surface of the epithelium. The olfactory epithelium has a thickness of about 150-300 microns. It is covered with a layer of mucus (10-50 µm) that odorant molecules have to overcome before they provisionally with special sensory neurons - olfactory receptors. The physiological functions of the mucus layer completely still not clear. No doubt that it creates a hydrophilic shell to the sensitive and fragile olfactory receptors, performing a protective function. After all, the system of perception of the signal needs to be protected from the external environment, that is, from molecules of odorants, some of which may be rather dangerous and chemically active substances.

Cilia-zilie directed obliquely to the outer surface of the layer of mucus. They form a kind of grid, with irregular cells, with the grid located at the interface of sublayers so that the main part of the surface of the cilia (about 85% ) Noi is located near the boundary of the partition.

To olfactory signal was received by the neuron, the odorant molecule binds with a special protein located in the neuronal cell membrane. This structure is called a receptor protein.

One of the models of the process of signal conversion inside the cilia of the olfactory neuron [2]

The olfactory system uses a combinatorial scheme for the identification of odorants and signal encoding. According to this one type of olfactory receptor is activated by multiple odorants and one odorant activates many types of receptors. Different odorants are encoded by different combinations of olfactory receptors, and the increase in the concentration of the stimulus leads to an increase in the number of activated receptors and the complexity of its receptor code. In this scheme, each receptor acts as a component of the combinatorial receptor code for many odorants, and performs the role of a kind of letter of the alphabet, the totality of which are appropriate words-smell.

Minimal structural differences of the molecules of odorants, e.g., functional group, carbon chain length, spatial structure lead to different receptor code. For the distinctive feature of the odorant molecule, capable to change the encoding of odor, was proposed the term "totop" (odotope), or the determinant of the smell. Different olfactory receptors that recognize the same odorant, can you identify the various signs-homotopy. A single olfactory receptor is able to distinguish molecules that differ in length of carbon chain by only one carbon atom, or molecules having same length of carbon chains but differ only in the functional group.

Activation of the receptor protein molecule of odorant ultimately leads to the generation of electric current in the olfactory receptor neuron. The current spreads through the dendrite of a neuron to its somatic part, which excites an output electrical pulse. This pulse is transmitted through the neuronal axon to the olfactory bulb, which serves as the first processing center of olfactory information in the brain.

Transmission of information about odors to the brain [2]

The olfactory bulb is a large multi-layered neural network for spatio-temporal processing of displaying the smell in the glomeruli. Depending on the content of the transmitted signal of glomeruli are activated in different ways. The combination of activated glomeruli is called a map of smell and is kind of "mold" smell, that is, it shows from which odorous substance is perceived by the olfactory object.

Properties of the olfactory cortex of the brain allow us to form an associative memory, which establishes a connection of the new fragrance with the fingerprints of the perceived olfactory stimuli. I believe that the process of identification of odorant includes comparing the resulting display its description in semantic memory. In the case of coincidence of the imprint and the memory of the odor takes place any response (emotional, physical) of the body. This process is performed very quickly, within seconds, and match information after the response is immediately reset, since the brain is preparing itself for the solution of the following problem of odor perception. [2]

Thus, it is possible to allocate sequential steps in human perception of smell:

  1. Peripheral Department of the olfactory analyzer: molecules of odorants diffuse into the area of the nasopharynx, and to influence the receptors, they must be adsorbed and dissolve in the moist surface of the olfactory epithelium. Further information on the stimulation of the receptors passes through the conductive path.
  2. The conducting tracts of the olfactory analyzer: the Olfactory cells, the receptor is provided with education at the end of their peripheral process, represent the first neuron pathways of the olfactory analyzer. Through the holes of the ethmoid bone, they are held in the cavity of the skull and penetrate the olfactory bulb, i.e., in a forward, thickened end of the olfactory tract. Here are the body of the second neuron. Axons of the second neurons form the olfactory tract and go to bodies of the third neurons are located in the amygdaloid nucleus, in the front, curved end of ammolofoi gyrus and in podozritel gyrus. Axons of the third neuron are sent to the cortical division of the olfactory analyzer.
  3. The division of cortical olfactory analyser, where there are cortical reflexes to olfactory stimulation.

It should be noted that the sensitivity of the olfactory analyzer varies considerably under the influence of various external and internal conditions. These changes either apply to the whole analyzer, or limited to individual cortical areas of his Department.

Psychology of odor perception

Many psychologists argue that people perceive odors two ways - natural (real) and imaginary, as any smell is in the minds of associative images associated with past events.

Depending on concentration, the same substance can have different effects.
In General, with increasing concentration of the volatile aromatic substances typical of the change of individual perception from neutral or pleasant (aroma), through indifferent, with an average "load receptors" — to the bad and the ugly (stink), "sensory overload".

There are effects in the perception of odors, as adaptation and interference.

  • Adaptation is a complete loss of sense of smell from a substance (as an example, hydrogen sulfide: it can be easily detected in minimal concentrations, not hazardous to health, but after a short time the strength of the sensation drops dramatically — to the extent that the person is not able to sense concentrations exceeding the permissible concentration in the air)
  • Interference – the superposition of several odors, which can significantly distort the overall assessment of the flavor.

In various diseases or in certain emotional States the person may experience olfactory illusions and hallucinations (for example, a person begins to feel burning smell like a citrus flavor).

Phenomena the illusory perception of smells also called hemoretseptornoy anesthesia (toning) or hyperesthesia (aggravation), they can occur at different times, some periodically (at the beginning of the menstrual cycle, after suffering a traumatic brain injury, severe nervous shock). [4]

In addition to the illusions, there could also be olfactory hallucinations. They often represent an imaginary perception of odors (one feels, for example, the smell of mold, vinegar or rotting), rarely – not a familiar scent, even less – the smell of something pleasant. In most cases, these effects arise as a result of various pathological processes.


This article has presented a brief information about the physiology and psychology of perception of odors.

The General principles of the perception of the known, but details are still not well understood and leave many questions.

We should note that often the smell of man is felt, but not understood.

Smell can be used to awaken some memories of people, even those that in the normal state it is hard to remember.

Odors play an important role in the formation of the world picture, however, there occur errors due to peculiarities of physiology and psychology.

Translated by «Yandex.Translator»

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