Basic Physiology of Acupuncture Needle Insertion (dry needling)

Written by Roger White on . Posted in Blog

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Four needles inserted and connected to an electro acupuncture stimulator.

Acupuncture is the practice of inserting thin needles into specific locations in the body to elicit a response.  Since nothing is being injected into the body (called wet needling), acupuncture is a form of dry needling. Needle insertions into the skin and muscle tissues created a cascade of physiological effects that provide therapeutic benefits. Needles can provide physiological influence locally, segmentally, extra-segmentally, and provide central regulatory effects.

When a needle is inserted into the tissues, the needle stimulates nerve fibers (Ad) which signals an axon reflex. This reflex releases vasoactive neuropeptides such as Calcitonin Gene-Related Peptide (CGRP), which provides vasodilation in the area. Evidence exists shortly after insertion when the needle becomes surrounded by small red patches of skin.

When the Ad fibers are stimulated, an opioid peptide called encephalin is released, ultimately blocking pain and producing segmental analgesia. The action potential move up the nerve to the spinal cord and depress dorsal horn activity. Further, segmental responses also impact the autonomic nervous system. In the short term, there is a sympathetic response in the segment. Long term, the dorsal horn is depressed and an autonomic block interrupts the autonomic reflex, reducing muscle spasm.

These action potentials continue up from the dorsal horn to the brain stem, where extra-segmental effects can be achieved. Signals continue to travel to the midbrain and have shown influence on the cerebral cortex, specifically the hypothalamus and limbic systems.

Additional positive effects are produced when needles are inserted into myofascial trigger points. Contrary to many thoughts, many classical acupuncture points coincide with myofascial trigger points. However, treating these areas can often leave the patient sore following treatment.

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CT scan of the wrist with classical acupuncture points labeled

There are many more areas that can be used for insertion sites, such as periosteum, nerve trunks and roots, to name a few. Acupuncture points can be thought of as neuroreactive sites (see image on right).  The image shows a CT scan with classical points placed by their anatomical locations.  Notice the color where these wrist points coincide.

Needling can also be used as a method of neuromodulation, where the effects are sustained on the cells over a period of time. Four opioid peptides can be produced when needles are inserted: b-endorphin (responsible for analgesia), enkelphin, dynormphin, and orphanin (also called endomorphin and nociception).

A classical Chinese medicine principle of treatment is to elicit de qi, the short lived sensation when the nerves are stimulated after needle insertion. Practitioners may choose to twist the needles with their fingers, but this can become cumbersome depending on the number of needles used in the treatment. Another way of increasing stimulation is through the use of electroacupuncture (see image above), where electrodes are connected to needles. Devices have frequency settings, and each frequency has a different physiological response. Research done by Han revealed 2 Hz frequency induced analgesia with b-endorphin, enkelphin and orphanin release on the m receptors. On the high frequency spectrum (80-100Hz), dynorphin was released on the k receptors.

Although needling might be considered ineffective or even placebo effect, physiology has proven responses from needles to occur, and these events can lead to changes in many health conditions.

Recommended Reading

An Introduction to Western Medical Acupuncture (2008) Adrian White, Mike Cummings, Jacqueline Filshie.



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