The olfactory system is much more useful and complex than it might seem.
The sense of smell is one of the five senses of the human body . It allows us to detect and interpret information related to the world in which we live, allowing us to enjoy pleasant odorous stimuli or warning us when something is wrong.
There is no doubt that it has been and still is a very important tool for survival, and this article explains the most important thing to know about this sense: what is the sense of smell and what is it for, and what are its parts and functions.
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What is the sense of smell?
Smell is a sense that allows us to perceive olfactory stimuli from the environment . This is possible thanks to chemoreceptor cells, which are capable of reacting to certain chemical characteristics of odorous substances.
In this way, these odorous molecules bind to the receptor endings of the neurons belonging to the olfactory epithelium. The more molecules, the more olfactory neurons that are activated, and from the nostril, this olfactory information begins to be transported to the brain through the cranial nerves.
When the brain has the nervous information, the brain can interpret the stimulus and understand its meaning in its context. For example, sometimes we may have food that has been in the fridge for a few days. If there are present substances typical of decomposition such as cadaverine or putrefactive, these can be tracked by the sense of smell and it is the brain that ultimately interprets this information.
Nerve and brain parts (and their functions)
The sense of smell is complex and consists of different parts . For the brain to identify and interpret a smell, there are different structures that fulfill their relevant functions, and only in this way is it possible to smell.
Below they are presented in a differentiated way to understand the path of information, from the reception of olfactory molecules to the rationalization of what they mean.
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1. Chemoreceptor cells
Chemoreceptor cells are the cells that are responsible for detecting olfactory molecules . They are found in the olfactory mucosa, an area of the nasal mucosa that has a yellowish pigmentation.
2. Olfactory neurotransmitters
The specialized neurons are prolonged into nerve fibers . These cross the ethmoid bone, at the roof of the nasal cavities, and extend into the olfactory bulb, a specialized organ for the sense of smell.
3. Olfactory bulb
The olfactory bulb is a very important functional part . This organ is capable of identifying what type of chemical code belongs to each sniffed molecule, subsequently sending the pertinent nerve signals to the brain.
4. Neurotransmitters in the brain
From the work of the olfactory bulb, the information reaches the brain directly . It is a transmission of information that has changed the code, and from here the brain can interpret this information about the environment.
5. Brain
The olfactory bulb is directly connected to different brain structures . The cortex is the area where most axons end, differentiating between the primary and secondary olfactory cortex.
Each and every one of them is shown below, as the nerve impulses are interpreted in different directions.
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5.1. primary olfactory cortex
Nerve signals reach the primary olfactory cortex, which processes the information . The nerve projections go directly there and do not go through the thalamus, unlike other sensory systems.
The primary cortex is the brain area that is responsible for the simplest and most primitive functions related to smell. For example, information passes through the limbic system, which makes smells relate to emotions and memories.
The hippocampus or the amygdala are some of the system structures that connect smells with all past personal experience and the world of emotions.
Other projections reach the nucleus accumbens and other centers of pleasure, gratification, displeasure and punishment, as well as those responsible for endocrine activity and the regulation of the desire to eat.
5.2. secondary olfactory cortex
The primary olfactory cortex sends processed information to the secondary olfactory cortex . This part is located in the frontal lobe, and it is where all the projections from the other brain areas converge.
The integration is such that it is also done with those primary areas that are responsible for the sense of taste, as well as the cognitive coordination of the control of the instinctive reflex. Eating behavior, then, can be modulated at a rational level through the prefrontal lobe.
In this way, the final connections allow the person to make decisions regarding the olfactory stimuli that they have smelled. The primary cortex is responsible for processing the information and giving a quick survival response when necessary, but the secondary cortex allows you to work at a cognitive level with this data to make the best decision.
conclusion
Smell is one of the five ways we humans perceive the external world . It is a complex sensory system that has evolved in parallel over millions of years through the different animals that inhabit planet Earth.
Some animals have a more acute sense of smell than others. For example, dogs or moles can collect much more olfactory information than humans. The reason is that it has been an evolutionarily more stable strategy for humans to develop sight than smell.
In this way, natural selection has made the development of the visual cortex prevail over the olfactory cortex in humans. Today, people rely much more on sight than smell to survive. Fortunately, we can still enjoy magnificent smells and detect when food smells bad and can harm us.
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Bibliographic references
- Guyton, AC & Hall, J.E. (2008). Treatise on medical physiology (11th edition). Madrid: Elsevier.
- Hoover, K. C. (2010). Smell with inspiration: the evolutionary significance of olfaction. Am J Phys Anthropol., 143(51), 63-74 .
- Jaeger, SR et al. (2013). A Mendelian Trait for Olfactory Sensitivity Affects Odor Experience and Food Selection”. Current Biology, 23(16), 1601-1605 .
To the classic question “what do you do?” I always answer “basically I am a psychologist”. In fact, my academic training has revolved around the psychology of development, education and community, a field of study influenced my volunteer activities, as well as my first work experiences in personal services.