The Nervous System · Part One · How It Is Built and Fueled
Lesson 01 / 61
The Neuron and the Central Integrative State: What Decides Whether a Cell Fires
What sets a cell's readiness, what feeds it, and what moves it.
The central integrative state is a neuron's readiness to fire, the net balance of every excitatory and inhibitory influence acting on it at one moment. It is a condition rather than a structure. A cell sitting near threshold answers a small signal, and the same cell drifted away from threshold ignores it. Pools of neurons, nuclei, and whole networks each hold a state of their own. The Unified Model of Tone identifies that state as tone read at the scale of a single cell.
Resting potential
About minus seventy millivolts
Two supplies
Metabolic fuel and afferent activation, both continuous
Brain fuel share
2 percent of body weight, 20 percent of oxygen
Failure mode
Excitability shifts before structure fails
The neuron
The functional unit of the nervous system. Dendrites gather incoming signal, the cell body integrates it, and one axon carries the result away. The verdict is a spike or silence, with nothing in between, so the whole of the work is in the weighing. A neuron reaches that verdict inside a chemical environment neighboring glial cells hold steady, which is why its readiness is never a property of the cell alone.
Summation
Inputs do not queue. Thousands of excitatory and inhibitory potentials arrive together and combine into a single change in membrane potential. The amplitude of each event sets part of the result, and summation in time and across separate regions of the dendritic tree sets the rest. In the Unified Model of Tone, a cell answers the pattern of its input rather than its loudest source.
01The neuron as decision unit
Every neuron weighs its input before it answers
The neuron is the functional unit of the nervous system, and its job is a verdict. Dendrites gather incoming signal, the cell body integrates it, and one axon carries the result onward. The answer is a spike or silence, so everything that matters happens in the weighing.
No neuron does that weighing alone. Its ion concentrations, its transmitter levels, and its fuel are held in range by the glial cells packed around it, which is why a cell's readiness can move while its own machinery stays intact. Neuroglia and the Neurovascular Unit counts those cells and describes what they hold steady.
The running balance is older than the recording
Charles Sherrington published The Integrative Action of the Nervous System in 1906 Grant 2007. Cajal and Golgi had argued the anatomy of the junction between neurons. Sherrington gave that junction a function. A cell adds and subtracts what reaches it, and the sum is what it acts on. The central integrative state is that sum given a name and a value.
The arrangement repeats upward. A balance held by one population of cells is read by the population above it as a single quantity, the way a whole dendritic tree reaches the axon hillock as one number. The Unified Model of Tone takes the repetition seriously, so a state held anywhere in the stack is legible to the level above it.
02Findings
What the research shows
Measured values for readiness, for the fuel that holds it, and for what happens when input stops.
03Summation at the dendrite
Thousands of inputs combine into a single change in membrane potential
No single synapse commands the outcome. Thousands of excitatory and inhibitory postsynaptic potentials arrive at once and combine into a singular change in membrane potential Magee 2000. Three elements set the result: the amplitude of each unitary event, the addition of events arriving close together in time, and the addition of events arriving in separate regions of the dendritic arbor. The output of a neuron is never a copy of one input.
That arithmetic is what a spike reports. Once the sum reaches threshold the cell fires, and the firing itself is all or none, which puts every meaningful difference on the input side of the threshold. The ionic account of the charge, the trigger zone, and the spike is set out in The Resting and Action Potential.
The same input fires a cell at one moment and leaves it silent at another
The consequence is the subject of this page. If the sum decides, then the state of the membrane at the moment a signal arrives is as much a determinant of the answer as the signal is. A volley that fires a cell at one moment leaves the same cell silent a second later, with the synapse, the transmitter, and the receptor all unchanged. The variable that moved has a name.
04The central integrative state
The central integrative state decides whether a message gets through
The central integrative state, or CIS, is the net readiness of a neuron to fire at a given moment. A cell with a high integrative state sits near threshold and answers easily. A cell with a low integrative state has drifted away and responds slowly, if at all.
One experiment carries the whole idea. At the mouse layer 5B to posteromedial thalamus giant synapse, knocking down the Cav 3.1 calcium channel subunit abolished the synapse's driver function at a typical resting potential of minus seventy millivolts. Depolarizing the membrane to minus sixty millivolts restored relay of single action potentials Seol 2015. Ten millivolts of background state, with no change in the incoming signal, decided whether the message arrived.
The idea scales upward. Pools of neurons, nuclei, and whole networks each carry an integrative state of their own, stacked one on another. A single cell and a whole brain can therefore be described in the same terms.
The state is readable in people, not only in slices
An evoked potential makes it visible. The N30 peak of the somatosensory evoked potential indexes sensorimotor integration rather than simple arrival, and spinal input moves it. In 96 adults with recurrent neck pain, a thrust at a clinician-selected segment lowered N30 by about 17 percent, while a thrust at a predetermined segment changed nothing Niazi 2024. In 12 subjects with subclinical neck pain, cervical manipulation lowered both N20 and N30 for about 20 minutes Haavik-Taylor 2007. A fall is the established direction. A crossover in 17 men with chronic stroke is the one sample that moved the other way, raising N30 by 39 percent while the N20 relay peak did not move Navid 2020.
The direction is not fixed, and no honest reading of those trials makes it fixed. What they share is the peak that moved. The integrative peak shifted in every case, in intact necks and in a brain reorganized by stroke, and it shifted upward in one population and downward in another. The model expects that result rather than apologizing for it. One class of input met two different starting states and moved a single integrative peak two ways, which is what a state-dependent reply looks like and what a fixed-direction claim cannot hold. Which segment the thrust lands on matters too, and the tone page carries that trial.
The Unified Model of Tone makes the identification directly. The central integrative state is tone read at the scale of a single cell, and tone is the same state read across a whole organism at once. The construct survives the change in resolution. The instrument does not.
Tone held inside its healthy range is health, because a neuron there keeps the freedom to move toward threshold and away from it as conditions ask. Tone driven outside that range is what manifests as illness, because a cell pinned at the top of its range answers everything, and a cell pinned at the bottom answers nothing.
05Fuel and activation
A neuron stays healthy only when fuel and activation both arrive
Two supplies keep a neuron alive, and it needs them at the same time. The fuel is metabolic. The brain represents 2 percent of total body weight and accounts for 20 percent of all oxygen consumption de Castro 2010. Its total demands run to at least 20 percent of the body's energy consumption Magistretti 2015. Signaling is the expense and firing is the largest line in it, so activation is metered rather than free. The Resting and Action Potential itemizes that bill.
Holding the resting charge is itself work, and the work becomes visible when it is interrupted. Partial inhibition of the sodium-potassium pump with dihydroouabain in rat hippocampal slices depolarized CA1 pyramidal neurons by 5 to 6 mV, then left them about 6 mV hyperpolarized Vaillend 2002. Resting input resistance fell 30 percent. Inhibitory postsynaptic potentials dropped to roughly 25 percent of control while the coupling from excitatory potential to spike rose, and the neurons fired in bursts. A pump running short does not kill the cell. It rewrites the cell's arithmetic, and the same arriving input now reaches threshold.
The reserve belongs to the glia
Glycogen is the major energy reserve in the brain and it sits almost exclusively in astrocytes Swanson 1993. In murine cortical cultures holding both neurons and glia, several hours without glucose produced widespread neuronal degeneration while the glia survived. Raising astrocyte glycogen to 2 to 3 times control levels beforehand attenuated the neuronal loss, and drawing that glycogen back down removed the protection. Astrocyte glycogen delivers substrate to neural elements during periods of intense firing Brown 2015.
Energy delivery is monitored in register with neuronal activity Magistretti 2015. The Unified Model of Tone reads fuel and activation as one requirement sampled at two points. A cell that fires more draws more, and the reserve it draws on is held by a neighbor, so readiness is a shared quantity before it is a cellular one.
06Deprivation and decline
A neuron deprived of input degenerates, and its territory is taken over
Cut the input and the target cell declines. After fimbria-fornix transection in adult rats, neuronal number in the medial mammillary nucleus fell by about 20 percent between 14 and 30 days, through transsynaptic apoptosis and sustained atrophy Ginsberg 2002. Somatodendritic pathology was still present at six months. Transneural degeneration is countable, it happens in the adult brain, and it does not reverse on a short clock.
The same course runs in primates. Deafferented cells of the lateral geniculate nucleus showed rapid transneuronal degeneration after enucleation in monkeys, across a series of seven infant and three adult animals Sloper 1987. Losing the eye cost the cells that read it.
The cortical map does not wait for a neuron to recover
Cortical territory is reassigned when its input stops. Somatosensory maps in adult macaques reorganized over 1 to 2 millimeters mediolaterally after limited deafferentation, and by an order of magnitude more after extensive long-term deafferentation Pons 1991. Silence is not held open for a region that stops reporting.
Afferent input is therefore a condition of the system's shape and not only of its moment-to-moment activity. Deprivation costs a neuron its own substance and its territory at the same time, which raises a practical question. Where does a nervous system get most of its activation?
07Adjustment as afferent input
An adjustment enters this machinery as afferent input
The answer is movement, and the largest single generator of it is the spine. It holds more movable joints than any other region, its deep segmental muscles are built to report position rather than force, and every segment that moves sends afferent traffic up through the cord and brainstem. The receptor densities behind that claim sit on input quality, and the receptor itself on Muscle Spindles and Proprioception.
This is the ground the practice stands on. We are the practice organized around the nervous system, and in the terms of this page an adjustment is a burst of proprioceptive input entered into the summation described above. What it changes first is a readiness rather than a tissue, on the timescale of neural signaling rather than repair. The measured outcomes of that input are collected on the tone page.
The Unified Model of Tone makes a claim that follows straight from summation. The reply to an input is set by the balance the input meets, so one thrust delivered to two people can move their integrative states in opposite directions without either result contradicting the other. Where the state sits before the input arrives selects the direction. The size of the force does not.
The model stakes itself on a claim this page can be held to. It holds that the readiness of one neuron, the readiness of the pool that neuron sits in, and the readiness read across a whole organism are one quantity measured at three resolutions. The state of one cell, the state of the pool it sits in, and the state read across the whole organism sharing one direction of change under one input is what establishes the identification, and the model with it.
The input does not decide the answer. The state that meets it does.
08Tone
How this system expresses tone
Every part of the nervous system expresses all of tone. At the scale of one cell it is written in millivolts, and three of the foundations can be read straight off the membrane.
Set point
A neuron defends a resting charge near minus seventy millivolts. Partially inhibiting the sodium-potassium pump in rat hippocampal slices leaves the cell about 6 mV hyperpolarized and hyperexcitable.
Gain
Distance from threshold sets how much input reaches output. Ten millivolts of depolarization restored relay at a mouse synapse lacking Cav 3.1. Gain holds the system-level ratio.
Input quality
What arrives decides what a cell keeps. Adult macaque somatosensory maps shifted 1 to 2 millimeters after limited deafferentation, and far more when the loss ran long.
The remaining six foundations show up in the same arithmetic. Oscillation: the spike is the carrier that moves the state, and what a downstream cell reads is the rhythm of firing rather than any single spike. Prediction: the balance a cell holds before a signal arrives is a standing bet on what is coming, which is why one synapse can be primed to relay and another primed to ignore. Load: signaling costs the brain 20 percent of the body's oxygen, so readiness is bought continuously and a shortfall is felt first as a change in excitability. Constraint: a neuron can answer only with the channels and receptors it currently carries, and removing Cav 3.1 removed a reply the synapse otherwise had. Coupling: the reserve a neuron draws on is glycogen held in astrocytes, so its readiness and another cell's metabolism are one arrangement. Time course: a spike lasts milliseconds, a manipulation-driven shift in cortical integration lasts about 20 minutes, and somatodendritic pathology after deafferentation is still visible at six months.
09Across the library
How this page relates to the rest of the library
Where a neuron's readiness is picked up elsewhere in the library.
The ionic account of the charge this page only names: pump stoichiometry, the axon initial segment as trigger zone, and the itemized energy bill for holding a membrane at rest.
The junction that generates those thousands of inputs, and how transmitter release is already graded before any summation begins.
The cells counted against neurons close to one for one, holding the ions, the transmitter clearance, and the glycogen a neuron's readiness runs on.
The receptor that generates spinal afferent traffic, including how gamma drive sets what a spindle reports before any thrust reaches it.
What a supply shortfall does over years rather than minutes, and the point at which a shift in excitability becomes structural loss.
Map reorganization read forward instead of backward, and what a deliberate schedule of input does to cortical territory that was given away.
Where the densest afferent supply sits, spindle density muscle by muscle, and what changes in the reports when a segment stops moving well.
10Frequently asked
Questions about this topic
What is the central integrative state?
The central integrative state is the readiness of a neuron to fire, measured in millivolts of distance from threshold. Ten millivolts can settle the question. At a mouse thalamic giant synapse with the Cav 3.1 channel knocked down, transmission failed at the resting potential. Depolarizing the membrane ten millivolts restored relay of single action potentials, with the incoming signal unchanged. The same running balance is held by pools of cells, by nuclei, and by whole networks, so the term applies at every scale.
How does a neuron decide whether to fire?
A neuron fires when the sum of what reaches its membrane crosses threshold. Thousands of excitatory and inhibitory postsynaptic potentials arrive together rather than in a queue, and they combine into a single change in membrane potential. The amplitude of each unitary event, the addition of events close together in time, and the addition of events in separate regions of the dendritic tree all shape that sum. Because the spike itself is all or none, every meaningful difference between one answer and another happens before threshold.
Why do neurons need constant input?
Neurons need two supplies, fuel and activation, and afferent traffic is the activation. After fimbria-fornix transection in adult rats, neuronal number in the target nucleus fell about 20 percent between 14 and 30 days, and somatodendritic pathology was still present at six months. Deafferented cells in the monkey lateral geniculate nucleus degenerate rapidly once the eye is removed. Somatosensory maps in adult macaques reorganize 1 to 2 millimeters when input stops, and far more when the loss is extensive. Activation is a condition of survival.
How much energy does the brain use, and on what?
The brain is about 2 percent of body weight and accounts for 20 percent of all oxygen consumption, with total demands running to at least 20 percent of the body's energy consumption. Signaling is what that budget buys, so firing is metered rather than free. Holding the resting charge is itself work: partially inhibiting the sodium-potassium pump in rat hippocampal slices left neurons bursting. The main reserve is glycogen, held almost entirely in astrocytes, so a neuron runs on a supply another cell stores.
Can the central integrative state be measured in a person?
The state is measurable in people with an evoked potential. The N30 peak of the somatosensory evoked potential reflects sensorimotor integration rather than simple arrival, and spinal input moves it. In 96 adults with recurrent neck pain, a thrust at a clinician-selected segment lowered N30 by about 17 percent, and a thrust at a predetermined segment changed nothing at all. A fall is the established direction across samples. One crossover in 17 men with chronic stroke raised it 39 percent instead, while the N20 relay peak stayed where it was.
What does a chiropractic adjustment do to a neuron?
In the terms of this page, an adjustment is a burst of proprioceptive input entered into a cell's summation. It does not repair a tissue on contact. It changes the balance a neuron is holding when the next signal arrives, on the timescale of neural signaling rather than healing, and the changed balance is what alters the reply. Because the spine generates more of this traffic than any other region, a segment that stops reporting well withdraws activation from the cells that depend on it.
Does an adjustment raise or lower excitability?
A fall in the N30 evoked potential is the established direction after spinal manipulation. It measured about 17 percent in 96 adults with recurrent neck pain, and it held for roughly 20 minutes in 12 subjects with subclinical neck pain. One crossover in 17 men with chronic stroke found a 39 percent rise instead. Within every one of these samples the spread runs close to twice the mean, so individual nervous systems already move in both directions around the average.
Is the central integrative state the same thing as tone?
The central integrative state is tone at the scale of a single cell. Neurophysiology already describes the cellular case as the running sum of every excitatory and inhibitory influence converging on a neuron, which sets how that cell answers the next signal. The Unified Model of Tone adds the identification. The same quantity read across every tissue at once is what the model calls tone, and only the instrument changes with the scale. Held inside its range, that readiness keeps a cell free to answer or decline.
11The sources
References
Sources: primary literature, linked inline.