Essential Oils and the Sense of Smell
The study of the sense of smell is called “osmology” from the Greek word “osme” meaning to smell. The system of the body that’s involved in the sense of smell is called the OLFACTORY SYSTEM.
SOME INTERESTING THINGS ABOUT THE SENSE OF SMELL: The sense of smell is evolutionarily the oldest sense and it evolved long before vision and hearing as a link to and a means of monitoring the external world.
In the evolutionary history of life, primitive organisms had a sense of smell before they had any other senses. Touch, vision, hearing, taste all came later.
Systems that have the oldest evolutionary history are those that are tied in to basic survival functions and drives. Animals in the wild would have a very hard time without a sense of smell because they couldn’t locate food or mates and they would have trouble avoiding dangers (rotten food, bad water, smoke, other animal’s territory).
People who lose their sense of smell can survive but they also have a hard time – they loose the ability to enjoy food and in a lot of cases sex drive is badly affected, menstrual cycles may be altered, and there may be depression.
Because the olfactory sense is very old, its connections to the oldest areas of the brain are relatively direct. No other sensory system gets signals into the brain with as few synapses as the olfactory system and no other sensory system communicates as directly with brain areas related to emotion and to hormonal and immune functioning.
FACTOIDS: Even humans can recognize their significant others (children, parents, mates, siblings) by smell.
Dogs cannot distinguish between clothing worn by identical twins but can distinguish clothing worn by non-identical twins.
Women can discriminate between armpit swabs (yuck!) taken from people who have watched happy movies vs. those who have watched sad movies. Men are less good at this.
Smell receptors have been identified in human sperm (they may smell their way to the egg).
The Department of Defense is spending money to develop odors so offensive that they will incapacitate people (with vomiting, avoidance, etc.).
HOW OLFACTION WORKS: Any substance that has a smell is emitting molecules into the atmosphere. When one of these molecules is inhaled, it moves into a nostril and passes first past the receptors of the Trigeminal Nerve (CN V), which act as “guards” by sensing irritating odors and triggering a sneeze.
Molecules that aren’t ejected by a sneeze are drawn into the nasal mucous, which is produced by the nasal epithelium. They dissolve in the mucous and are then taken up by tiny olfactory receptor cells that live in the epithelium. In humans, there are about 6 million of these cells in each nostril (about 50 million for a rat).
Olfactory molecules can also reach the nasal epithelium through the mouth.
ONE THEORY OF HOW ODOR MOLECULES INTERACT WITH THE RECEPTOR CELLS: The olfactory receptor cells contain proteins and one theory is that the unique combination of proteins in an individual cell acts as a “lock” for that cell – each kind of lock has a different shape and can only be opened by those aroma molecules that have the same shape. The protein configurations of all our receptor cells are encoded by as many as 1000 different genes, accounting for 2% of the human genome ( indicating the importance of smell)
What this means is that not every receptor cell is activated by every odor molecule and so any given odor molecule will activate only a few receptor cells, in a pattern that’s unique to that odor.
The problem with this theory is that in the early 1980’s it was discovered that some odor molecules, such as those of Eucalyptus globulus, are too large to fit into ANY of these “protein locks”, yet they are still perceived. So there is still debate on how this really works. As early as 1870, Ogle proposed that the pigment found in the nasal passages might act to absorb the molecular vibrations of odor molecules and convert these vibrations into signals that could act on the receptor cells – we still don’t why there’s pigment in the olfactory epithelium.
The theory of molecular vibration was picked up again by Dyson in 1938 and is still being considered.
At any rate, when the olfactory receptor cells are activated they carry signals into the olfactory bulb, where they synapse on 2nd order neurons (called mitral cells). These second order neurons group together to form the olfactory tract and travel further into the brain, where they synapse again with cells in the prepiriform cortex and the amygdala. From there they travel to the hypothalamus and other brain areas.
The areas of the brain that are receiving these signals from the olfactory nerves are areas of the brain that are involved in emotion, memory, immune function, basic drives, and hormonal functioning and the important thing about this set-up is that it creates a very close link between odors, emotions, subconscious processes, memory, hormonal activity, immune system function, and autonomic processes in general.
Heart rate, breath rate, and blood pressure can be almost instantaneously altered by aromas.
Olfactory signals carried to the thalamus may stimulate the release of enkaphalin, a pain killer and mood elevator.
If the signal is carried to the locus ceruleus in the brainstem, it will stimulate the action of norepinephrine, which will help to lessen fatigue and stimulate the immune system.
If it’s an odor that stimulates the Raphe nucleus in the brain stem it will have opposite effects – it’ll stimulate the release of serotonin which has a sedative action and helps to relieve anxiety, insomnia, and high blood pressure.
In the pituitary gland, a specific odor could stimulate leutenizing hormone, or follicle stimulating hormone or ACTH (adrenocorticotrophin) which controls growth hormones, cortisol, and thyroid stimulating hormone.
There is nothing that you can take by mouth that will affect any of these systems as quickly as inhaling something will.
RESPONSE TO ODORS IS OFTEN LEARNED: Many odors trigger automatic responses – e.g., irritating odors make you sneeze or pull back – but our responses to many other odors are learned, usually unconsciously. If an odor has been paired with a traumatic experience in a person’s life, that odor will provoke the physiological responses associated with the trauma every time it’s smelled.
This is why you must always respect a client’s individual, instinctive response to an odor, no matter how illogical it seems and no matter how otherwise appropriate the oil would be.
If smell is associated with a positive, healing treatment, then in some cases, the smell can be effectively used as a substitute for the treatment; blood glucose is effected this way by pairing insulin injection with a smell.
If you’re a qualified psychotherapist, exploring idiosyncratic reactions to aromas can sometimes open up repressed memories and lead to the release of those emotional traumas.
HOW INHALATION OF ESSENTIAL OILS COMPARES TO PHARMACEUTICAL DRUGS: Essential oils that are inhaled in normal use don’t have the knock down power of pharmaceutical psychotropics – they’re not going to act as “brain Novacaine” the way Valium will, but if you’re practicing a holistic form of therapy you already know that knock down drugs don’t heal anything – this isn’t the effect we want to get in a holistic therapy.
Exceptions to the knock down rule: inhalation of camphor or large amounts of menthol can cause instant collapse in infants. Some people with seizure disorders may have seizures from inhaling certain oils.
INHALATION AND THE RESPIRATORY SYSTEM: When you’re inhaling essential oils, in addition to going to the brain, they’re also going through the respiratory system and down into the lungs, where they are taken up into the circulatory system.
Inhalation of essential oils is also a good way to approach respiratory infections because it brings the oils into direct contact with the tissues of the respiratory tract; and it will eventually exert systemic effects as the oils enter into the circulatory system.
Copyright © 2011 Joie Power, Ph.D. / The Aromatherapy School | All Rights Reserved
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