When we inhale essential oils (or any other aroma), small aromatic molecules are transported through the nasal cavity through olfactory nerves to the olfactory epithelium-tissue, which unites millions of sensory neurons. Neuronal cells contain proteins called receptors that capture aromatic molecules. The receptors are like locks that are unlocked with the aromatic molecules passing them.
People have about 450 different types of olfactory receptor (dogs, for example, have twice as many).
Once the aromatic molecule connects to the receptor, it initiates an electrical signal that passes from the sensory neurons to the olfactory bulb (a structure at the base of the brain which then transmits the signal to other parts of the brain for further processing). This signal goes to an area located just behind the olfactory bulb whose job is to recognize the fragrance. Aromatic information is also sent to the thalamus, whose function is to recognize all the sensory information coming to the brain. The thalamus is the switchboard, which, depending on the type of aromatic molecule, quickly sends a signal to specific brain areas.
These instant sings, which the thalamus sends to other brain parts, cause certain emotional responses and bring back certain memories to our memory.
Each of us has experienced a fragrance that reminds him of an ex-boyfriend, for example. This happens because the thalamus sends fragrant information to the hippocampus and amygdala, which are two of the major brain centers associated with memory and learning. On the other hand, aromatic molecules of citric essential oils, for example, bind to the prefrontal cortex and have a stimulating and waking effect on the mind.
The effects that aromatic molecules exert on our brains explain why we feel more vigorous and energetic when we feel the aroma of coffee or grapefruit and more relaxed when a lavender scent rises around us. All this happens before rational brain centers are activated and not a conscious process. But the knowledge of how aromas affect our brain, and hence our emotional state, energy levels and our ability to remember, can serve as a basis for the use of essential oils in our everyday life.