The body’s fastest signalling network — how a message travels, where it slows down, and why a scent reaches you before you have named it.
~13 min read
Everything a body does needs telling. Some of it is slow and chemical, carried in the blood over minutes and hours — the endocrine system. The rest is fast, and it is this one: a message travels out and back in a hundredth of a second, which is how your hand is away from something sharp before you know what it was.
It does everything with one trick, repeated in parallel: a cell carries an electrical change along its length, then hands the message chemically to the next. The gap is where everything interesting happens, because anything that ever influences a message influences it there.
Anatomy divides it by location: the brain and spinal cord encased in bone, and the peripheral nerves threading out to a fingertip or a stomach wall. Eighty-six billion neurons; the brain is two per cent of body weight and takes twenty per cent of resting energy.
The organs and structures involved
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The last of the four is not a place: the autonomic nervous system is the set of nerves doing the work you never decide.
Brain
About 1.3 to 1.4 kilograms, roughly sixty per cent fat by dry weight. Less one organ than a stack: brainstem for breathing and heart rate, deeper structures for drive, memory and feeling, the folded outer sheet for thought.
Spinal cord
As thick as a finger, 43 to 45 centimetres long. A cable, and a decision-maker: a reflex is settled in the cord and acted on before the signal reaches the brain.
Peripheral nerves
Axons bundled in connective tissue. Twelve pairs leave the brain and thirty-one the cord, reaching every square centimetre of skin, every muscle and every organ wall.
Diagram to come
One neuron drawn left to right at full width — dendrites, cell body, a myelinated axon with visible gaps between segments, axon terminal — then a magnified inset of the synapse showing vesicles fusing at the terminal membrane, transmitter molecules crossing a narrow gap, receptors on the receiving cell. The inset must make the gap look small but genuinely empty; the emptiness is the point. One arrow for direction along the axon, none in the inset.
Neurons are only about half the cell count. The rest are glia — support cells that insulate axons, clear debris and regulate what crosses from blood into brain tissue. The insulation is myelin, a fatty sheath wrapped around an axon in segments, and it is why a signal travels fast.
A resting neuron is not doing nothing — it is holding a difference. Pumps push three sodium ions out for every two potassium ions in, spending ATP, and the inside settles at about minus seventy millivolts: a loaded spring, maintained every second of your life.
An incoming signal nudges that voltage up, and most nudges fade. But at roughly minus fifty-five millivolts — the threshold — sodium channels snap open and the inside swings to plus thirty or forty millivolts, before potassium leaves and the membrane settles. A stronger stimulus makes more spikes, never a larger one: intensity is coded as frequency.
It travels at half a metre per second along a bare fibre, up to about 120 metres per second where it can leap between insulation segments. Then it stops: neurons are not soldered together, there is a gap of twenty to forty nanometres, and charge does not cross empty space. Calcium enters the terminal, neurotransmitter empties into the gap, and those molecules bind receptors opposite.
Notice what that costs in raw materials. The spike is sodium moving in and potassium moving out; transmitter release is triggered by calcium. DHA, an omega-3, is built into the membranes all of it happens across, and a membrane made from one kind of fat is more or less fluid than one made from another, so the proteins sitting in it sit differently. Thiamin is needed where glucose enters the energy cycle, and nerve tissue runs almost entirely on glucose; vitamin B6 is the cofactor for enzymes that build several neurotransmitters from amino acids; vitamin B12 is required for normal formation of myelin, with folate alongside it.
Why build a slow chemical step into a fast electrical system? Because it is the only place a message can be edited — amplified, damped, made to excite the next cell or quieten it. Anything chemical that influences this system acts at a gap, not along a wire. The endocannabinoid system lesson is the clearest example.
Two halves pull in opposite directions, and most of what a healer notices is a question about the balance between them.
The sympathetic half prepares for effort; the parasympathetic half runs recovery, and most of that falls to one nerve — the vagus, wandering from the brainstem to heart, lungs, stomach and intestine.
| Sympathetic | Parasympathetic | |
|---|---|---|
| The job | Get ready to act | Recover, repair, digest |
| Heart | Faster, harder | Slower, softer |
| Breathing | Quicker, higher | Slower, lower |
| Digestion | Slowed | Resumed |
Gear is a better word than switch: neither half turns off, only the balance shifts. Since repair and digestion happen on the recovery side, sitting too far toward effort costs you somewhere that looks unrelated — eating while wound up is not the same act as eating at rest, which is why the digestive system returns to this one.
The one lever you can actually pull
Breathing is the only autonomic function you can also run deliberately. You cannot decide to slow your heart or start digesting, but you can decide how you breathe, and the breath is wired into the same circuitry. A slow breath out is the one deliberate lever on an otherwise automatic system, and nothing in a bottle substitutes for it.
Diagram to come
One body outline down the centre. Sympathetic outflow on the left leaving the middle of the spine into a chain of ganglia; parasympathetic on the right leaving the brainstem as the vagus nerve and branching to heart, lungs, stomach and intestine. Beside each target organ a paired marker showing what each side does to it. Both sides must read as permanently present rather than one on and one off — do not draw either as a switch.
The sympathetic side works through nerves leaving the middle of the spinal cord, which release noradrenaline at their targets, while the adrenal glands add adrenaline to the blood — which is why the effect outlasts the moment that caused it. The parasympathetic side works almost entirely through the vagus, and that gives it a handle.
Heart rate is not steady even at rest: it rises as you breathe in and falls as you breathe out — respiratory sinus arrhythmia. The reason is mechanical. Vagal traffic to the heart is reduced during inspiration and restored during expiration. Breathing in eases the brake off; breathing out puts it back on.
So the two halves of a breath are not equivalent, and lengthening the exhalation raises the share of each cycle spent under vagal influence. Four counts in and six or eight out, at five or six breaths a minute, is the usual shape; the mechanism is in the ratio, not the count. It is also why a scent and a breath are so often paired.
An honest ranking. Nothing below is a product.
Those five outrank anything in a bottle, which is worth saying plainly on a platform that sells bottles. No aroma out-argues a fortnight of four-hour nights. What an oil can do is sit inside those habits and mark them: a scent used at the same point each day becomes part of the signal that the point has arrived.
A nervous system is built from fat, run on glucose and signalled with minerals.
Tap any of these for its own page.
Fat first. The brain is around sixty per cent fat by dry weight, and that fat is structure rather than storage: every neuron is wrapped in a membrane of two facing layers of fatty molecules, and every myelin segment is many such layers wound tight. Fat quality is a nervous-system question, not a waistline one.
Food first — oily fish, eggs, leafy greens, nuts and seeds. A supplement fills a gap rather than replacing a plate. Nutrition and the Body Systems maps what each of the nine draws on.
The minerals are not supporting cast — they are the signal. Magnesium sits in the mouth of certain receptor channels, potassium is half the resting charge difference, and calcium is the trigger at every gap.
Smell is the only sense that reaches the feeling parts of the brain before the thinking parts.
An essential oil constituent is volatile — airborne at room temperature — which is why aromatic use is possible at all. Breathe in, and some of those molecules settle into receptors on the sensory neurons at the roof of the nasal cavity, and those neurons fire.
Then the part that makes this sense different from every other. Sight, sound, touch and taste route first through the thalamus, a relay in the middle of the brain, and only then reach the cortex. Smell does not: projections leave the olfactory bulb straight into the limbic system — the amygdala, which handles emotional significance, and the entorhinal cortex, the doorway to memory.
A human carries roughly four hundred working olfactory receptor types, and a molecule fires a neuron by fitting the one shaped for it. Aroma is not the only route in: constituents also cross the nasal and lung lining into the blood, and cool or sharp sensations travel the trigeminal nerve rather than the olfactory one — which is why peppermint feels cold on a wrist whose temperature has not changed.
Olfactory sensory neurons are unusual twice over: in direct contact with the outside world, and replaced every month or two. Their axons pass up through a sheet of bone perforated like a sieve and end just above it in the olfactory bulb, gathering into roughly spherical structures, each collecting from neurons of the same receptor type.
So nothing in the nose identifies lavender. Hundreds of different molecules arrive, each nudging a different subset of those four hundred receptor types, and what leaves the bulb is a pattern across them. Recognition happens downstream, on the pattern. Which is why lavender is instantly recognisable and almost impossible to describe.
Why a scent reaches feeling before thought
A smell lands in the emotional and memory structures of the brain before the part that names it — which is why a scent can bring back a whole afternoon from thirty years ago a moment before you can say what you are smelling. Not mysticism: a projection that skips a relay.
Diagram to come
Side view of the head, nose at left, sectioned so the route is visible end to end: airborne molecules entering the nasal cavity; the olfactory epithelium at the roof with sensory neurons in the mucus layer; axons passing up through the perforated bone; the olfactory bulb with its spherical sorting structures. Then TWO paths leaving the bulb at clearly different weights — a short bold one straight into the limbic structures (amygdala, entorhinal cortex to hippocampus), and a longer thin one going on to the thalamus and then to the naming region of the cortex. Alongside, faint and separate, the ordinary route every other sense takes: sense organ to thalamus to cortex. A reader must be able to tell at a glance that one route has a step the other skips.
A route is not a result. Everything above is settled anatomy, in any physiology text and not contested. What happens after a molecule arrives is far less settled. Much of the published work on individual constituents is done in laboratories, on cells in a dish or in animal models, and a result in a dish is not a result in a person. Human studies tend to be small, short and hard to blind — a participant can tell whether a room smells of lavender.
What the route does justify is that aroma is not decoration: a molecule from a plant reaches a structure in your brain by a describable path, in seconds. See The Oil Effect.
Read these as chemistry: a base note lingers because its molecules are heavier, a top note is brief because they are light. Terpenes has the names.
Adaptiv — Calming Blend
Wild Orange, Lavender, Copaiba, Spearmint, Magnolia, Rosemary, Neroli and Sweetgum. doTERRA formulated it around the accumulation of small demands that builds across a long day, using oils historically valued for supporting a calm, centred state of mind without dulling alertness — hence spearmint and rosemary among the florals.
Bergamot — Citrus bergamia
Cold pressed from the rind. 20–55% limonene gives the brightness, but it also carries 10–45% linalyl acetate and 3–20% linalool — lavender’s ester and alcohol, which is why it reads bright and settled at once. Being expressed citrus: avoid direct sunlight or UV for up to twelve hours after applying it to skin.
Peppermint — Mentha piperita
30–50% menthol and 15–30% menthone. A sharp top note, and its cold sensation is a receptor effect rather than a temperature one — peppermint has the account. Dilute heavily for children and keep it off a young child’s face.
Lavender — Lavandula angustifolia
From the flowering tops: 25–45% linalyl acetate, 20–47% linalool and 0.3–10% ocimene — an ester and a monoterpene alcohol carrying most of the aroma. A middle note. See lavender.
Copaiba — Copaifera officinalis
45–65% beta-caryophyllene, the highest in the range, and it binds directly to CB2 receptors — the endocannabinoid system has that story. Almost no aroma of its own, so it disappears into a blend rather than leading one.
Frankincense — Boswellia species
From hardened resin: alpha-pinene, limonene and sesquiterpenes. A long-lasting base note, warm and resinous, that layers under anything.
Vetiver — Vetiveria zizanioides
From the root, and among the most chemically complex oils there is, built around the sesquiterpene alcohols isovalencenol, khusimol and vetiselinenol. The heaviest base note here: deep, earthy, smoky.
Cedarwood — Juniperus virginiana
10–47% cedrol plus other sesquiterpenes, from the wood. Warm, dry and woody: a base note that holds a blend down.
Balance — Grounding Blend
Spruce, Ho Wood, Frankincense, Blue Tansy, Blue Chamomile and Osmanthus, carried in fractionated coconut oil. Ho wood is linalool-rich; blue tansy carries the chamazulene that gives the blend its colour. Already diluted, so it goes onto skin as it is.
Serenity — Restful Blend
Lavender, Cedarwood, Coriander, Ylang Ylang, Marjoram, Roman Chamomile, Vetiver, Hawaiian Sandalwood, Tonka Bean and Vanilla — florals on top, woods and root beneath, two sweet absolutes holding them together.
Topical use means diluted — one to two drops in a teaspoon of carrier oil, less on delicate skin and less again on children. Internal use is never assumed: only an oil whose label states it is for internal use should be taken that way. Labelling differs across markets, as does which products are sold.
Three moments. The habit is the structure; the oil marks it, which makes it easier to keep.
Morning
Light first — outside if you can, ten to twenty minutes, within an hour of waking. Then three to four drops of Adaptiv in a diffuser, or Balance on the soles of the feet.
The afternoon dip
Alertness and core temperature both fall in the early afternoon as part of the daily rhythm. The strongest response is to go outside and move for ten minutes: light and effort in one action. Alongside it, a drop of Adaptiv inhaled from the palms.
The wind-down, and the bedroom
Most of the leverage is here, and most of it is subtraction: lower the light, put the screen down, stop eating. Then Serenity in the diffuser thirty to sixty minutes before sleep, or a drop of lavender on the pillow — a base note is still there at two in the morning, a citrus is not. Thirty minutes, not overnight. At the same hour each evening, that turns a nice smell into a signal.
Photograph to come
A bedside table in low, warm evening light: a diffuser giving off a thin plume, one 15 mL amber bottle beside it, a book face-down, the lamp the only light in the room. Real and slightly lived-in — not styled, no labels turned to camera, no hands. It must read as the last twenty minutes of an ordinary day.
Some things are not a household question, and knowing which is part of being good at this.
None of those is a failure of what you have been learning. A healer at home works in the wide territory of ordinary days — a demanding week, occasional sleeplessness, an evening you cannot put down. A qualified practitioner works where examination and tests are needed, and knowing where your own territory ends is the strongest part of this.
This is education about how a body is built and how it works. It is different from professional medical care and does not replace it. Reading Your Own Body turns a vague sense that something is off into an observation specific enough to tell someone.
Keep oils away from eyes and inner ears, and out of reach of children. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before use. Nothing here is intended to diagnose, treat, cure or prevent any disease.
Lesson 5 of 11 · Body Systems