If there was adequate neuronal potentiation to nociception causing an action potential, stimulation to second and third order neurons (specifically, the VPL and CNL of the thalamus) nociception would take place,1 eventually signaling the post-central gyrus as well as the association cortex.
To continue on our education of the nociception afferent system, there are three major ascending pathways. The one which we have just explained would be the spinothalamic tract, which originates from neurons in laminas I and V-VII and is comprised of axons of nociceptive-specific and wide dynamic range neurons. A second pathway would send two-thirds (or 66%) of nociception to the reticular formation in the medulla; a third tract would send nociceptive afferents to the mesencephalic periaqueductal grey.2
When dealing with head and facial pain, these scenarios take on a different perception to the patient than pain of the elbow. People tend to tolerate more of the latter. The concomitants of head and facial pain seem to be different than other localization of pain.
With head and facial pain, as with a classical migraine, localization appears to be shared by two different nerves. Sensorially, the face is innervated by the general somatic afferent portion of the trigeminal nerve,3 and the head is supplied by C2 and C3 dermatomes.4 So to perceive these areas of pain simultaneously, both sensory nerves thus stated would be brought to the threshold.
With receptor potentiation that exceeds threshold, causing an action potential to nociception, the flexor-reflex afferent system is stimulated, thus causing reflexogenic myospasm of the related segmental musculature via stimulation of the alpha motor neuron.5,6 As pertaining to the head and facial pain, spasm of the suboccipital and posterior cervical (as well as the trapezius muscles) occurs.7,8
Joint fixation or aberrancy of movement of vertebral segments can also set up these pain patterns, so how could chiropractic serve to reduce these scenarios? With lack of vertebral motion, there coexists a decrease in receptor potentiation from joint mechanoreceptor (Merkel's, Meissner's and Pacinian corpuscles)9 as well as reduction of peripheral receptor potentiations. Since pain modulation could be segmental or suprasegmental, the correlation exists between a reduction in this modulation and reduction in sensory receptor potentials.
Chiropractically speaking, any therapeutic activity that increases this sensory perception will cause a presynaptic inhibition at the dorsal horn, as well as the release of enkephalins and endorphins caudally and rostrally. This is what is referred to as segmental and suprasegmental modulation of nociception.
Coupled reduction vertebral adjustments will cause an increase in neuronal propagation of joint mechanoreceptors to the thalamus and caudal representations achieving this goal. Specifically, with head and face pain and the duality of nerve function in this area via cranial nerve 5 and the upper cervical neuromeres at C1-C3, adjustments in this area would cause a presynaptic inhibition to nociception in this region. Once the vector of vertebra joint misalignment has been calculated and the proper line of correction instituted in this part of the spine, alleviation of the pain syndrome (as well as an increase in the central integrated state of the neuraxis) would be achieved. The knowledge of the neuraxis is essential for the clinical care of the patient, as well as the verification of importance of the science, art and philosophy that is chiropractic.
- Kandall, Schwartz, Tessel. Principles of Neural Science, chapter 27.
- Wilson, Pauwels, Akesson, Stewart. Cranial Nerves: Anatomy and Clinical Components, chapter 5.
- Kandall, Schwartz, Tessel. Principles of Neural Science, chapter 25.
- Kandall, Schwartz, Tessel. Principles of Neural Science, chapter 38.
- Guyton. Basic Neuronal Science, chapter 16.
- Kendall, McCreary. Muscle Testing and Function.
- Kandall, Schwartz, Tessel. Principles of Neural Science, chapter 5.
Paul F. Stefanelli, DC, DACNB
Belleville, New Jersey