Smell is one of the most underrated senses. The perception of smells affects what and how much we eat. The sense of smell warns of dangers. Odors affect our sexual behavior. What is the mechanism of human perception of different smells, how can the human sense of smell be assessed and what problems can lead to an olfactory disorder?

Contents:

  1. Smell: anatomy and physiology
  2. Smell: functions
  3. Smell: examination
  4. Smell: odor disorders

The smellin the past did not attract much attention of scholars - yes, its meaning was known, but it was not attributed to this sense of playing any greater role in human functioning.

However, with time and the research carried out, it turned out that the role of the sense of smell is much greater than one might imagine.

It is worth mentioning here that the genes that code only the olfactory receptors constitute about 2% of the entire human genome.

The sense of smell in humans is definitely not as developed as in animals, it is also not as sensitive as in animals, but still the sense of smell and related processes are quite complicated and simply essential for human functioning.

Smell: anatomy and physiology

Fragrances are nothing more than volatile compounds that reach the nasal cavity with the air, and more precisely to the olfactory epithelium inside it.

It is located within the nasal cavity - on each side, on the left and on the right, and covers an area of ​​approximately 2.5 cm².

In this relatively small area, there are a large number of receptors for fragrances - it is estimated that in humans there are up to 50 million of them in the nasal cavity.

There are several types of cells within the olfactory epithelium (olfactory field), which are bipolar, support and basal cells.

The role of the receptors is played by bipolar cells, each with a dozen or so cilia. They are immersed in the mucus that covers the olfactory epithelium - the fragrances reaching this area dissolve in it.

An important particle in the mucus is the odorant binding protein (OBP).protein), the task of which is to transport odorous particles reaching the nasal cavity.

Bipolar cells, as the name suggests, have two poles - the axon projections emerge from the second of them, which ultimately form the so-called olfactory threads. They go to the next cells belonging to the olfactory tract, until finally the stimuli received by the olfactory receptors reach the olfactory centers located within, among others, gyrus of the hippocampus and the amygdala and cortex of the brain.

Different people are characterized by different sensitivity to scent stimuli - this is a kind of individual trait. Overall, however, it is estimated that the average person is able to feel about 10,000 different smells.

Smell: functions

Smelling tasks stand out for far more than one might imagine.

First of all, it has a protective function - thanks to the sense of smell, a person is able to identify smells that indicate a threat, which may be a signal for him to escape (such as a burning smell).

The sense of smell is also important when consuming food - the way a dish smells, for it has an impact on whether we reach for it at all, but also whether we like it.

The sense of smell also regulates the secretion of saliva and gastric juice during food intake.

The functions of smell are clearly visible from the moment a person comes into the world.

It is thanks to the sense of smell that the newborn is able to recognize its mother, the sense of smell is also important in initiating the reflex to suck the mother's breast.

Interestingly, smell can regulate sexual activity in people, pleasant smells can also … mobilize to make intellectual effort.

Smell: examination

Theoretically, the smell test seems simple, but in practice it is not.

Difficulties in assessing the sense of smell are mainly due to the fact that the smell test is quite subjective - after all, it is the patient himself who tells whether he feels the smell or does not feel it at all.

During the classic olfactory assessment, the subjects were given to smell substances with characteristic smells, e.g. vanilla or ammonia solution.

This type of analysis allows for a basic assessment of the functioning of the sense of smell in a given person, but they do not provide full information about how a given patient actually smells.

Fortunately, studies are now available that allow you to evaluate far more detailed aspectsregarding the sense of smell - we are talking about tests that allow you to determine:

      • odor identification threshold (it determines the lowest concentration of a given substance that allows the patient to recognize it)
      • odor detection threshold (informing about the lowest concentration of a given substance that is felt by the tested person)
      • odor discrimination threshold (to assess what the concentrations of two or more different fragrances must be for the patient to consider them as separate odors)

The above-mentioned parameters are evaluated in tests which are also subjective. However, it is possible to carry out objective olfactory tests, which are the study of olfactory potentials and the electro-phactogram.

Visualization of the olfactory bulbs is possible in imaging tests (such as, for example, magnetic resonance imaging), the activation of the olfactory centers in response to odorous stimuli can also be assessed using positron emission tomography or functional magnetic resonance.

Smell: odor disorders

Smell disorders can take various forms - it happens that the patient struggles with a weakened perception of odors (hyposmia), does not feel them at all (the condition is called anosmia), in addition, hypersensitivity to smells is also possible (a problem called hyperosmia).

In humans, there may also be kakosmia, i.e. the perception of unpleasant olfactory sensations, there is also parosmia, which is characterized by incorrect perception of smell sensations.

It is also possible for people to develop olfactory hallucinations, i.e. the feeling of smells that are not really there.

A patient who has an olfactory disorder for a long time should definitely visit a doctor - there are many possible causes of such a problem and they can include:

      • neurological diseases (e.g. Parkinson's disease, multiple sclerosis or Alzheimer's disease, migraine headaches, epilepsy)
      • diabetes
      • chronic sinusitis
      • damage to the olfactory epithelium (caused, for example, by smoking or the abuse of nasal decongestants)
      • tumors of the central nervous system (especially tumors located in the frontal lobe)
      • genetic diseases (e.g. Gaucher disease)
      • kidney disease
      • mental illness (e.g. schizophrenia)

In the case of olfactory disorders, it is necessary to search for their cause, because it is usually necessary to cure themfocusing on the problem that led to them.

In the diagnosis of olfactory disorders, it is necessary not only to perform appropriate tests to assess the sense of smell, but also to collect a history with the patient about the time from which the olfactory disorders occur (especially their sudden onset is worrying), the medications they take and diseases that is burdened and used by him stimulants (especially alcohol and cigarettes).

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About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.

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Category:

Neurology