Neurophysiology of Chiropractic

Research has demonstrated that chiropractic care is successful in treating spinal injuries [1-7], yet many doctors are unable to adequately describe how or why that is the case. This ambiguity leads medical providers to lack confidence in knowing who, when, or why to refer to a
chiropractor. This is a review of the technical explanation of the neurophysiology of spinal injuries, as well as how properly applied chiropractic treatment is effective at reversing the deleterious effects of such injuries.

When examined in closer detail, one can see that chiropractic treatment stimulates spinal
joint mechanoreceptors, which in turn decreases nociceptive activation, decreasing pain, increasing joint and tissue ranges of motion, decreasing muscle spasm, and joint stiffness. The goal is to provide the reader with a better scientific understanding of why chiropractic is effective.

Nociceptors – The Pathway to Pain
Virtually all structures in the spine, including the outer 1/3 of the disc, are innervated by nociceptors [8, 9]. Injury to one or more of these structures, through repetitive microtrauma or acute microtrauma, sensitizes nociceptors, either mechanically, or by the release of inflammatory cytokines like prostaglandin E-2,
leukotriene B-4 and bradykinin [10, 11]. These nociceptors release substance P in the substantia gelatinosa of the spine, which results in pain, sympathetic hyperactivity, and reflex muscle spasm [12-16].
a. Sympathetic Hyperactivity – In addition to causing local and referred pain, nociceptive input causes the release of norepinephrine by the postganglionic sympathetic nerve fibers at the segmental level [17].
The release of norepinephrine causes inflammation, vasoconstriction and hypoxia [18]. Hypoxia in tissues
leads to adhesion formation which results in joint stiffness, which eventually can lead to scar tissue and
degeneration [19, 20].
b. Reflex Muscle Spasm – Nociceptors have direct entry to the alpha and gamma-motor neurons [21]. Nociceptive stimulation and sensitization of somatomotor neurons results in local muscle spasm [12]. It is important to note that the resulting superficial muscle spasm is a natural, compensatory reaction which serves to protect the injured joint and avoid further damage [22-25]. These patients think they have
“pulled a muscle in their back”, and are unaware that the muscle pain and spasm they feel is not the cause of the problem, but rather a result of nerve irritation due to joint injury. Consequently, it is not wise to direct treatment solely at reducing muscle spasm with muscle relaxants, massage, or
physical therapy, as that may lessen the normal protective mechanism and worsen the original injury.
Mechanoreceptors
Aside from nociceptors, the other main category of joint receptors is mechanoreceptors (MR’s) [26]. MR’s, such as golgi tendon organs and muscle spindles, are activated by movement and stretch and relay information about position sense and proprioception to the CNS [27]. Like nociceptors, MR’s are found in the vast majority of spinal structures and they terminate in the substantia gelatinosa of the spine [28]. Unlike nociceptors however, MR’s are larger, faster A-beta fibers which compete with, and block
the uptake of substance P by nociceptors at the substantia Gelatinosa. This is the basis of Gate Control Theory, which suggests that when MR’s are stimulated, they “close the gate” for uptake from nociceptors
[29]. Therefore, anything which stimulates MR’s, such as chiropractic treatment (manupaltion/IQ Impulse) or therapeutic massage will inhibit pain, reduce muscle spasm, and inhibit sympathetic activation; effectively restoring normal joint function and
reducing symptoms.

Chiropractic Treatment
Chiropractic physicians have long sought (with history, examination, palpation, x-ray, CT and MRI analysis), to identify areas of the spine with spinal irritation, tightness, and/or pain and muscular guarding [30, 31]. When seen on x-ray, these vertebrae can appear tilted, rotated, or shifted out of “normal” position. Such biomechanical changes can cause uneven or increased unilateral facet joint
loading, which irritates the facet joint capsule, causing nociceptor activation [32]. Additionally, spinal irritation can create disc wedging, desiccation or drying out of the disc and lead to disc bulging and herniations [33]. As mentioned previously, such injuries cause pain, muscle spasm, and joint adhesion formation.
For many years, chiropractors told their patients that the goal of treatment was to “re-align the spine” to take pressure off the nerves. While that occurs to some degree, the benefit of chiropractic treatment lies more in restoring normal joint motion in the spine, effectively stimulating mechanoreceptors, reducing fear avoidance due to painful joint movement, reducing pain, lessening muscle spasm, breaking up joint adhesions, and normalizing joint function.

Our office primarily utilizes high velocity, low amplitude manipulations wherein a gentle, quick force is applied to the joint, keeping the joint within the limit of passive range
of motion, Impulse IQ- stimulation of the joint MR’s without “popping” the spinal joints or moving them mechanically, traction or spinal decompression therapy, ultrasound, extracorporeal therapy, massage therapy and other modalities. In doing so, the specific chiropractic manipulation momentarily gaps the facet joints, breaking up intra-articular adhesions, stimulating mechanoreceptors, and improving normal biomechanics of the joint [34-38]. In addition, nearly every patient we see is given specific stretching exercises to stimulate joint mechanoreceptors and a core strengthening or activation program to stimulate the spine and reduce facet joint strain. Together with treatment, the right exercises can enable the patient to return to activities of daily living and avoid further injury or need for treatment.
Chiropractors have been successful in treating spinal injuries for more than a century, but until recently, have been unable to describe exactly how or why that is the case. While there is a great deal more
neurophysiology involved than one page can thoroughly address, hopefully the reader has a better understanding of the science behind chiropractic treatment, and feels more confident in referring patients
who may benefit from its success.

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