It was chiropractic’s progenitor D.D. Palmer who set the table for the profession by singling out the nervous system as the Holy Grail of what health care practitioners should be addressing in managing their patients.1
Palmer declared that:
“Life is the expression of tone. In that sentence is the basic principle of chiropractic. Tone is the normal degree of nerve tension. Tone is expressed in functions by the normal elasticity, activity, strength, and excitability of the various organs, as observed in a state of heath. Consequently, the cause of disease is any variation of tone—nerves too tense or too slack.”
Such was to point out that disorders of the nervous system—no matter how subtle—governed changes in health and, if left unattended, emerged as symptoms and ultimately as pathologies. By lending itself to an assortment of noninvasive tests designed to pinpoint the area of neural dysfunction, which then helped identify the optimal pathway to activate that area, the nervous system as identified by Palmer served as the blueprint for chiropractic.
Yet for so many years, neurological status seemed to lurk in the shadows, while seeming to take a back seat to spinal fixations. Thus, it was a breath of fresh air to witness the spanking new, progressive recasting of the chiropractic definition of the subluxation appearing in the fourth edition of the Clinical Practice Guidelines issued by the Council on Chiropractic Practice, which reads: “Subluxation is a neurological imbalance or distortion in the body associated with adverse physiological responses and/or structural changes, which may become persistent or progressive. The most frequent site for the chiropractic correction of the subluxation is via the vertebral column.”2
The term neurological imbalance speaks volumes and serves as the keystone of chiropractic neurology. Neurological imbalance supersedes so many of the ossified terms defining the subluxation that used to be grounded in segmental, articular, or vertebral terms from the 1930s to at least 60 years afterward.3 A more accurate way to capture the essence of chiropractic is to consider the term functional neurology, founded on the principle of neuroplasticity, in that nerve connections in the brain may be modified or shaped by an extensive variety of afferents, including sensory, cognitive, emotional, or motor experiences—and are thus amenable to rehabilitation.
The focus of functional neurology is its conceptualization of the nervous system as an integrated network that controls the homeostasis of the body through balanced signaling, free from the distortions that could lead not only to neurological, neurodevelopmental, or demyelinating diseases but also to movement disorders, balance and equilibrium problems, headaches, cerebrovascular conditions, and traumatic injuries.4 The aspect of functional neurology that gives us hope is that a reorganization of nerve cells is possible to restore or bypass connections that have become disrupted or damaged. An apt example of this would be the series of exercises a patient is prescribed to recover from a stroke or spinal manipulations to alleviate sciatica.
Chiropractic neurology: At the neuronal level
Drilling down to the locus of neurological rehabilitation, turn your attention to the neuron.5 Here, it is a matter of assessing the likelihood that the neuron will produce an action potential, depending on its state of polarization, which in turn depends upon the sum total of the excitatory and inhibitory stimuli that it encounters at any given moment.
If the neuron is depolarized, for example, the cell has become more positive internally, minimizing the potential difference across the membrane and thereby moving the neuron toward its firing threshold. The opposite, of course, is the hyperpolarized state in which the cell interior has become more negative, increasing the potential difference across the membrane and causing the neuron to back away from its firing threshold and attenuating the transmission of neural impulses.
Alterations in the balance between de- or hyperpolarization of the neuron (the neuroaxis) in response to changes in the immediate or external surroundings have been known since 1964, when the histology of the rat cerebral cortex was found to respond to environmental changes.6 This phenomenon became recognized as neuroplasticity—the reorganization of nerve cells that is the core concept of functional neurology. This is no idle conjecture, as it was over 30 years ago that the World Health Organization recognized the accumulation of research findings and acknowledged that neuroplasticity could play a role in the repair of the central nervous system and thus might be a factor in effective health care interventions.7
Furthermore, it has been shown that neuroplasticity is not limited to neural injury and recovery, but encompasses:
- Dendritic remodeling,
- Synapse turnover,
- Long-term potentiation,
- Long-term inhibition, and
Indeed, the model of neuroplasticity in its focus on changes in the central nervous system has been proposed to be the missing link to our understanding of chronic musculoskeletal disorders.8
The gatekeeper of neurotransmission
The progression of this discussion from chiropractic neurology through functional neurology and neuroplasticity finds its molecular grounding in two components:
- The agent responsible for both receiving and regulating the signals that pass from neuron to neuron in neurotransmission is the receptor. Receptors function as agents of up or down-regulation, depending upon the molecules that they bind to. In this fashion, the receptor becomes the veritable gatekeeper of neurotransmission.
- In neurology, the signal passing from receptor to receptor is the neurotransmitter, a chemical substance released at the end of a nerve fiber by the arrival of a nerve impulse and which, by diffusing across the synapse or junction, produces the transfer of that nerve impulse to the adjoining neuron.
Because the receptor is primarily a high-molecular-weight protein, it needs to be studied by many of the same approaches that are taken in enzyme chemistry and regulation. This approach would involve considerations of genetic deletions, what are known as allosteric regulation and subunit analysis, and specificities of binding substrate molecules (called ligands) to these receptors.9,10 These components become the tools for understanding the regulation of neurotransmission, such that we are then able to clarify a number of basic mechanisms involved in neuroplasticity, of obvious interest to the chiropractor.
Those neurotransmitters most prominent in the human body are:
- Acetylcholine: The best-known neurotransmitter.
- Gamma amino butyric acid: The primary inhibitory neurotransmitter in the mammalian central nervous system, thus playing a key role in modulating neural activity.
- N-methyl-D-aspartate: A leading molecule species for controlling synaptic plasticity.11
- Dopamine: The primary neurotransmitter in the brain, affecting gene expression, expression of neuropeptides, regulation of motor movement control, and mediation of behavioral responses to rewarding stimuli.
- Serotonin: It regulates mood, activating the hypothalamic-pituitary axis, and controlling glucose balance and bone metabolism.
Indeed, a chiropractor at a recent seminar pointed out that becoming familiar with neurotransmitters “blew his mind,” with the effect of overturning the paradigm with which he viewed health care.12 This modern approach to chiropractic neurology not only stimulates key research needed to further validate chiropractic, but also provides key insight into defining that elusive yet omnipresent concept in every chiropractor’s mind, the chiropractic subluxation.
Anthony Rosner, PhD, is a champion of interdisciplinary research methodology in the health sciences, having previously served as director of research and Education at the Foundation for Chiropractic Education and Research, He was designated as Humanitarian of the Year in 2000 by the American Chiropractic Association and holds an honorary degree from the National University of Health Sciences. He obtained his PhD from Harvard in Medical Sciences/Biochemistry. He can be contacted at firstname.lastname@example.org.
1 Palmer DD: (1910). Text-book of the Science, Art and Philosophy of Chiropractic for Students and Practitioners. (p. 7). Portland, OR: Portland Printing House Company.
2 Council on Chiropractic Practice. (2013). Clinical Practice Guidelines. (4th ed.). Lexington, SC: CCGPP.
3 Gatterman M. What’s in a Word? (1995). In Gatterman M [Ed.]. Foundations of Chiropractic Subluxation. (pp. 5-17). St.Lous, MO: Mosby-Year Book.