It has been said that one of the aspects of healthy living is freedom from pain. Technically speaking, this is when the amplitude of receptor potentiation is less than necessary to stimulate the second order neuron of nocioception.
If there was adequate neuronal potentiation to nocioception causing an action potential, stimulation to second and third order neurons (specifically the VPL and CNL of the thalmus) nocioception would take place,1 eventually signaling the post central gyrus as well as the association cortex.
To continue on our education of the nocioception afferent system, there are three major ascending pathways, the one which we had just explained would be the spinothalamic tract which originates from neurons in laminas I, V-VII and is comprised of axons of nocioceptive specific and wide dynamic range neurons.
A second pathway would send 2/3 or 66% of nocioception to the reticular formation in the medulla and pons and a third tract would send nocioceptive afferents to the mesencephalic periaqueductal gray.1
When dealing with pain and its syndromes, we are really encountering second autonomic concomitants such as increased sweating, heart rate, respiration, change of bowel time, pupil dilation and nausea, just to name a few. Obviously, there are neuronal connections to the nuclei that cause these concomitants.
When dealing with head and facial pain these scenarios take on a different perception for the patient than pain of the elbow, for example. People tend to tolerate more of the latter. The concomitants of head and facial pain seem to be different than other localizations 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 nerve2 and the head is supplied by C2 and C3 dermatones.3 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 nocioception, the flexor-reflex afferent system is stimulated, thus causing reflexogenic myospasm of the related segmental musculature via stimulation of the alpha motor neuron.4,5 As pertaining to the head and facial pain, spasms of the suboccipital, posterior cervical and trapezius muscles occur.5,6
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 co-exists a decrease in receptor potentiation from joint mechanoreceptor (Merkel, Meissner, and pacchionian corpuscles),7 and a 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 enkephalons and endorphins release caudally and rostrally. This is what was referred to as suprasegmental and segmental modulation of nocioception.
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 nocioception 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 and 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, and the verification of importance of the science, art and philosophy of that is chiropractic.
References
- Kandall, Schwarts, Tessel. Principles of Neural Science, Chapter 27.
- Wilson, Pauwels, Akesson, Stewart. Cranial Nerves Anatomy and Clinical Comments, Chapter 5.
- Kandall, Schwarts, 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.