This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
2001 Third Web Report
Acupuncture, very basically, is the insertion of very fine needles, sometimes in conjunction with electrical stimulus, on the body's surface, in order to influence physiological functioning of the body (1). At the basis of acupuncture, is the theory that the body has a constant energy force running through it. This energy force is known as Qi. The Qi consists of all essential life activities which include the spiritual, emotional, mental and the physical aspects of life (5). People who practice an receive acupuncture therapy believe that a person's health is influenced by the flow of Qi in the body. It is believed that energy constantly flows up and down pathways in the body called Meridians. When these pathways become obstructed, deficient, excessive, or just unbalanced, Yin and Yang (positive and negative energy in every person) are said to be thrown out of balance (4). This causes illness. Acupuncture is said to restore the balance (1).
Meridians are described as special pathways of energy. The Meridians, or channels, are the same on both sides of the body. The acupuncture points for each disorder are specific locations where the Meridians come to the surface of the skin, and are easily accessible by "needling." (6) (3). The method of acupuncture usually used for pain relief and prevention is electro-acupuncture, which funnels very small electrical impulses through the acupuncture needles (1). For anyone who knows something about pain perception, the concept of Meridians is intriguing. It is also interesting how this Qi energy can be justified by the nervous system. Could it be equivalent to the constant flow and cycle of action potentials? Is it just how we describe these events in Western medicine as having a definite beginning and end that prevents us from seeing the body as an endless cavern of energy? How do pain pathways as described by modern medicine relate to acupuncture's effects?
Western Pain Pathway
Noxious stimuli such as pain, for the most part, activates nociceptors in the skin. Nociceptors are specialized sensory receptors that provide information about tissue damage. Not all activation of nociceptors is necessarily perceived as pain (11). Pain is a subjective experience that doesn't necessarily allow for a perfect correlation between nociception and pain perception. However, nociceptor activation is thought to be the first step in the process of pain perception (13).
Nociceptors are the least differentiated of the sensory receptors in the skin. They exist as free nerve endings that don't have a peripheral structure. Pain is mediated by several different nociceptive fibers. A-delta fibers are small and myelinated, while C fibers are unmyelinated. It is the C polymodal nociceptor that is thought to be most sensitive to a variety of painful stimuli including thermal and mechanical. Both A-delta and C fibers are distributed in the skin and deep tissue of humans. A noxious stimulus activates the nociceptor by depolarizing the membrane of the sensory ending. The exact mechanism by which different types of noxious stimuli depolarize a nerve ending and activate an action potential is not known (11).
The afferent fibers of nociceptors terminate on projection neurons in the dorsal horn of the spinal cord. Both A-delta and C fibers branch into two sections upon entering the dorsal horn. Branches of these axons ascend and descend for a few segments before their collateral's synapse primarily in the superficial dorsal horn of the spinal cord, which comprises the marginal zone (lamina I) and the substantia gelatinosa (lamina III). Nociceptive fibers then form connections with three classes of neurons in the dorsal horn: projection neurons that relay sensory information, excitatory interneurons that relay sensory input to projection neurons, and inhibitory interneurons that regulate nociceptive information to higher regions of the central nervous system. It is possible that acupuncture works by activating these inhibitory interneurons in the dorsal horn of the spinal cord (13).
Painful input to the dorsal horn is relayed to higher brain centers by projection neurons. Once in the thalamus, two major subdivisions of thalamic nuclei receive inputs from spinal projection neurons, the medial nuclear group and the lateral nuclear group. The response properties of the neurons in these two subdivisions are similar to those of the spinothalamic neurons that synapse on them. Therefore, some neurons in the lateral thalamus respond only to noxious stimuli, while others are able to respond to a wide range of somatosensory information. Neurons in the lateral thalamus project to several regions of the ipsilateral cortex and the somatosensory cortex where they are perceived as pain (13). Now that we have discussed the descending pain pathway we should examine suggestions as to how acupuncture causes analgesia in this pathway. Does it target the nociceptors? Is the dorsal horn and inhibitory interneuron the point of acupuncture analgesia? How can we try to relate a Western medicinal pathway with an Eastern medicinal philosophy that somehow has remarkable effects?
Acupuncture in Analgesia
A study performed by Malzack in 1977 showed a 71% correlation between trigger points for painful stimuli and acupuncture points used in pain therapy. In addition, observations in cadavers in China revealed that among the 324 points studied: 99% were within .5mm from innervation of a cranial spinal nerve such as the ones involved in descending pain pathways, and 96% were this closely related the peripheral nerves used in exogenous pain perception (12). These findings indicate a close relationship between the nervous systems pain pathways and acupuncture.
There are many theories as to how acupuncture has its analgesic effects. One theory of acupuncture analgesia suggests that acupuncture generates its analgesic effects through afferent sensory stimulation (14). According theories in pain stimulation, large A-Beta fibers which mainly carry touch sensation will inhibit transmission of small A- Beta C fibers which have been found to transmit pain (13). There is also a suggestion that acupuncture analgesia is caused through endogenous opioids that are released from the anterior pituitary such as Beta-endorphin. Beta-endorphin has been found to bind to analgesic receptors in the dorsal horn of the spinal cord causing pain inhibition (14). Additionally, acupuncture's analgesic effects have found to be diminished by administration of naloxone, a pharmaceutical substance that blocks they effects of Beta- endorphin in the spinal cord (10) (8). Another theory of analgesia mediated through acupuncture suggests that Meridians that are so full of energy are closely related to the gap junctions of neurons (7). It is thought that these synapses that connect neurons are the places of highest energy in the nervous system and thus the place when Meridians must lie (9). This suggestion links acupuncture to pharmacology. Many drugs, including psychotropic and pain relievers have their effects at the synapses of neurons as a re-uptake mechanism or prolonging effect. This theory would suggest that acupuncture works on the nervous system by a similar mechanism to create analgesia.
The question that can be asked of all these theories and pathways is, is it possible? Is it possible to attempt a connection of a Western medicinal pathway that is as well established as the pain pathway and insert an Eastern medicinal philosophy based on energy and balance. Will the two ever connect? Or, is it simply typical of Western medicine to find something that works and attempt to explain it through or own mechanisms. It is possible that acupuncture cannot be explained by Western medicine? It is possible that we may just have to accept the Eastern explanation. When you think about it, the entire basis of explanation is in error when you attempt to remove a medical philosophy from it's original context.
In Western society, for the most part, we do not believe that there is such a things as Qi and that diseases are caused by the lack of balance between the positive and negative energies residing in every person. Therefore, it makes it difficult to use another medical basis, such as a pain inhibitory pathway to describe the effects of this phenomenon that is based on another belief system. I believe at its core it is arrogance and cannot be done. While Eastern and Western medicine are often described as equal and opposite sides of the same coin, I question whether it is only our arrogance as a Western society that causes us to feel the need to explain everything from out own set of guidelines (2). Perhaps neurons and synapses can't be related to pressure points and Meridians and perhaps we should stop trying to always make it fit.
In a time of great neuronal discovery where neuroscience seems to always be the 'hot topic' in medicine I think we may be getting a little ahead of ourselves. Yes, the brain may totally equal behavior and biology may totally equal disease in our culture, but these are our rules and methods of understanding and until Western medicine can speak intelligently about things such as energy and mindfulness and stress and all these things that seem to be keeping other cultures healthy, we have no right to say things such as acupuncture cannot be explained. They just cannot be explained RIGHT now by US. In my opinion, this is an important distinction to make.
2)A Comparision of Eastern and Western Medicine
3)Clinical Point Explanation
4)A Reappraisal of Acupuncture
5)Acupuncture and Oriental Medicine Alliance
6)The Mechanism of Acupuncture
7)Neuronal Possibilities , Neuronal Diagram
8)Beyond Endorphins , Endorphins in Pain Mediation
9)Mechanism of Acupuncture: Beyond Neurohumoral Theory
10)Dr. L. Soh , Beyond Endorphins in Acupuncture Analgesia
12)Chronic Pain Solutions The Scientific Basis Of Acupuncture
13)Molecular Insights into the Problem of Pain
14)What We Know About Pain
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