What is an olfactory system and how it works?

 What is an olfactory system and how it works?

The olfactory system - our sense of smell, is the sensory system used for smelling (olfaction). Olfaction is one of our most powerful senses and is directly associated with specific organs. Most mammals and reptiles have a main olfactory system and an accessory olfactory system. The main olfactory system detects airborne substances, while the accessory system senses fluid-phase stimuli. The olfactory system is responsible for our sense of smell.

The senses of smell and taste (gustatory system) are often referred to together as the chemosensory system because they both give the brain information about the chemical composition of objects through a process called transduction.

This sense, also known as olfaction, is one of our five main senses and involves the detection and identification of molecules in the air.

Once detected by sensory organs, nerve signals are sent to the brain where the signals are processed. Our sense of smell is closely linked to our sense of taste as both rely on the perception of molecules. It is our sense of smell that allows us to detect the flavors in the foods we eat. Our sense of smell can ignite memories as well as influence our mood and behavior and it develops during our first 10 years of age.

Sense of smell is not only sensed through our nose. We also have smell receptors under our skin, which means we can sense anything through smell. It`s been researched that our day consists of 75% of different smells that we detect and smelling is very vital for our living, that's why it is named the most powerful.

Olfactory system structures

Our sense of smell is a complex process that depends on sensory organs, nerves, and the brain. Structures of the olfactory system include:

• Nose: opening containing nasal passages that allow outside air to flow into the nasal cavity. Also a component of the respiratory system, it humidifies, filters, and warms the air inside the nose.

• Nasal cavity: cavity divided by the nasal septum into left and right passages. It is lined with mucosa.

• Olfactory epithelium: specialized type of epithelial tissue in nasal cavities that contains olfactory nerve cells and receptor nerve cells. These cells send impulses to the olfactory bulb.

• Cribriform plate: a porous extension of the ethmoid bone, which separates the nasal cavity from the brain. Olfactory nerve fibers extend through the holes in the cribriform to reach the olfactory bulbs.

• Olfactory nerve: nerve (first cranial nerve) involved in olfaction. Olfactory nerve fibers extend from the mucous membrane, through the cribriform plate, to the olfactory bulbs.

• Olfactory bulbs: bulb-shaped structures in the forebrain where olfactory nerves end and the olfactory tract begins.

• Olfactory tract: a band of nerve fibers that extend from each olfactory bulb to the olfactory cortex of the brain.

• Olfactory cortex: area of the cerebral cortex that processes information about odors and receives nerve signals from the olfactory bulbs.

Our sense of smell

Our sense of smell works by detecting different odors. Olfactory epithelium located in the nose contains millions of chemical receptors that detect aromas. When we inhale, chemicals in the air are dissolved in mucus. Odor receptor neurons in the olfactory epithelium detect these odors and send the signals to the olfactory bulbs. These signals are then sent along olfactory tracts to the olfactory cortex of the brain through sensory transduction.

The olfactory cortex is vital for the processing and perception of odor. It is located in the temporal lobe of the brain, which is involved in organizing sensory input. The olfactory cortex is also a component of the limbic system. This system is involved in the processing of our emotions, survival instincts, and memory formation. This also means that the limbic system is the oldest part of our brain and when the olfactory cortex is part of the limbic system then it means that odors affect directly the emotional part of the brain. And if some odors can be repulsive then some odors can be relaxing, calming, soothing, etc.

The olfactory cortex has connections with other limbic system structures such as the amygdala, hippocampus, and hypothalamus. The amygdala is involved in forming emotional responses (particularly fear responses) and memories, the hippocampus indexes and stores memories, and the hypothalamus regulates emotional responses. It is the limbic system that connects senses, such as odors, to our memories and emotions.

The memory part is also very interesting, which means that all the smell memories are installed into our brain. All the bad memories, good memories with the taste of grandmother's cake or father's good perfume, etc. It also means that you can reinstall old memories with new smells and recreate a new anchor if needed.

Sense of Smell and Emotions

The connection between our sense of smell and emotions is deeply linked because olfactory system nerves connect directly to brain structures of the limbic system. Odors can trigger both positive and negative emotions as aromas are associated with specific memories.

Additionally, studies have demonstrated that the emotional expressions of others can influence our olfactory senses. This is due to the activity of an area of the brain known as the piriform cortex which is activated before odor sensation.

The piriform cortex processes visual information and creates an expectation that a particular fragrance will smell pleasant or unpleasant. Therefore, when we see a person with a disgusted facial expression before sensing an odor, there is an expectation that the odor is unpleasant. This expectation influences how we perceive the odor. Plus absolutely every person smells odors differently. For some can be a bad odor and very repulsive, but for others, it's totally ok.

Odor Pathways

Odors are detected through two pathways. The first is the orthonasal pathway which involves odors that are inhaled through the nose. The second is the retronasal pathway which is a pathway that connects the top of the throat to the nasal cavity. In the orthonasal pathway, odors enter the nasal passages and are detected by chemical receptors in the nose.

The retronasal pathway involves aromas that are contained within the foods we eat. As we chew food, odors are released that travel through the retronasal pathway connecting the throat to the nasal cavity. Once in the nasal cavity, these chemicals are detected by olfactory receptor cells in the nose.

Should the retronasal pathway become blocked, the aromas in foods we eat cannot reach odor-detecting cells in the nose. As such, the Wflavors in the food cannot be detected. This often happens when a person has a cold or sinus infection.