***This is a series of articles written by Chris Kresser, I’m posting them here because I have yet to find a better commentary on the modern understanding of acupuncture and Chinese medicine. If you enjoy his writing, you can visit him at chriskresser.com.***
In this article we’re going to take a closer look at one of the latest theories on how acupuncture relieves pain. I’m going to break it down in plain language for my readers who don’t have a scientific background, but I’ll also provide references at the end of the article for those of you that want the nitty-gritty detail.
Keep in mind that pain research is a constantly evolving topic, and more is being learned each year about the mechanisms of pain relief via acupuncture. (Although as an interesting side note, according to Professor Bruce Pomeranz of the University of Toronto, we know more about acupuncture analgesia than many chemical drugs in routine use. For example, we know little about the mechanisms of most anesthetic gases but still use them regularly.)
What I’m going to share with you here represents the latest information from the American Academy of Pain Management and papers published in major peer-reviewed journals.
The physiology of pain
Before I explain the mechanism, I have to give you a little background on the physiology and neurology involved.
There are two types of nerves involved in our perception of pain: sensory (nocioceptive) and position (proprioceptive) nerves. Both of these nerve types are firing at the same time in an area where we’re experiencing pain. These nerves travel to the spine and pass their information on to neurons in the spinothalamic tract. This tract travels up the lateral dorsal horn of the spinal cord to the mid-brain.
The sensory nerves register pain. The position nerves tell the brain where that pain is coming from. So the sensory nerves say “ouch!” and the position nerves say “my knee!”.
There are two different types of sensory nerves involved in the acupuncture response. There are A-Delta fibers, which transmit sharp, burning pain messages. And there are C-fibers, which transmit dull, throbbing pain messages. A-Delta fibers are responsible for acute pain, and the signals they send are short-lived. They fire for a while and then the signals die off. C-fibers are responsible for chronic pain, and fire over an extended period of time.
A-Delta fibers are surrounded by a fatty, myelin sheath and the signals they send travel at 60 ft/second (that’s fast!). C-fibers are unmyelinated and their signals travel at 20 ft/second.
The A-Delta fibers mediate what is known as the “gamma loop”. The gamma loop is what gets activated when you stick your hand in a fire and your hand jumps back. These nerve fibers respond so quickly that your hand is immediately pulled back out of the fire. Chronic pain is a C-fiber problem, so C-fiber signals don’t travel quite this quickly.
Now, if the signal strength of the position nerves (the ones that register the location of pain) is what it’s supposed to be, the brain will release powerful natural pain relieving substances called enkephalins when it starts to receive those C-fiber messages. The enkephalins then plug up pain receptor sites in the brain, spine and capillary beds where the pain is located. This stops the pain in its tracks.
When things go wrong
Unfortunately, this is not what happens in people with chronic pain. Why? The current explanation is that the position nerve signal going up to the brain is too weak. The mid-brain can’t figure out where the pain is coming from, so the enkephalins don’t get released. This is why people in chronic pain often have trouble identifying exactly were the pain is. The neural threshold of the position nerve pathway is too low, so these people aren’t getting a clear signal where the pain is emanating from.
Because the brain isn’t getting the message, the nerves keep firing. And keep firing. After a while the nerves become inflamed, which in turn further weakens the signal’s ability to jump the threshold and get the message to the brain.
So that’s the first problem. The nerve signals are too weak and aren’t stimulating the brain to release the natural painkillers.
The second problem involves a survival mechanism that the brain evolved a very long time ago. Let’s take a knee injury as an example. When we bang our knee into something, the brain immediately takes measures to protect it. The brain doesn’t know what happened to the knee, but it assumes a worst-case scenario. Maybe you were bitten by a poisonous snake, or perhaps you seriously cut your knee and are losing a lot of blood.
What the brain does in this situation is restrict the blood supply going into the knee and the blood return coming out of the knee. This is actually a very intelligent choice. If you were bitten by a venomous snake, reducing blood flow around the knee will lessen the chance that the poison will spread. And if you were cut badly, reducing the blood flow will lessen your chances of bleeding to death.
This phenomenon is known as “guarding”. One of the results of reducing blood flow to the knee is that it becomes stiff and weak (sound familiar?). The brain wants it to feel weak because it is attempting to protect the knee. The brain doesn’t want whatever happened to the knee to threaten your chances for survival. So the brain sacrifices the health of the knee in order to keep you alive.
This was a great strategy before the advent of western emergency medicine. Almost everyone would prefer to lose function in their knee to death. But this isn’t a choice most of us have to make anymore, because when we cut our knee or get bitten by a snake we can go to the hospital and they can save our lives. And the problem is that cutting off blood flow to the knee – while it may have saved our lives in times past – dramatically limits the knee’s ability to heal.
Why? Because everything we need to heal is in the blood. The blood contains analgesics (painkillers), anti-inflammatories, nutrients absorbed from food, oxygen, hormones and immune substances to fight infection. If the blood flow is restricted to a particular area, healing won’t occur. No blood flow, no healing.
Stop and think about this for a minute. It’s such an obvious fact that it’s often overlooked in medicine. It’s not taught in such a direct way in medical school, but when I’ve explained it to a couple of doctors they both said something to the effect of, “Huh. I never thought of it that way, but it makes perfect sense.”
How acupuncture helps
Okay, now we’re finally coming to the part where I explain how acupuncture fits into this picture. Inserting needles into the skin at peripheral sites “jumps” the neural threshold on the position nerve pathway, so that the signal can reach the brain. Once the signal reaches the brain, the whole series of events I described in the paragraphs above kicks in. The brain recognizes there is pain and where it’s coming from and releases enkephalins (painkillers).
This initial response is very fast. It should be perceived as almost instantaneous by the patient. But after the needling therapy the patient goes home and the pain comes back. The old bad habit of the nerve chronically firing below the threshold re-establishes itself. The body, just like the mind, has a hard time breaking bad habits.
But if the patient returns in a couple of days to get another treatment, the neural threshold will be jumped again. And if you keep jumping the neural threshold, eventually the central and peripheral nervous system figure out that it’s better to operate in the non-pain state than in the pain state. The technical term for this is re-establishment of neurological homeostasis.
Once this happens, the brain is no longer receiving pain signals from the knee. It no longer thinks the knee is injured or threatening the survival of the body. Now, instead of restricting blood flow to the knee, the brain does the opposite. It immediately vasodilates the capillaries and venules around the knee, which increases blood flow and begins the healing process.
What I’ve described above is how acupuncture relieves pain via the peripheral and central nervous system. There’s another pain relief mechanism that involves activating the immune system. Acupuncture needles are seen as foreign invaders to our body. Inserting a needle into the skin creates a micro-trauma that in turn stimulates the activity of immune cells that control inflammation.
There are millions of immune cells called mast cells in the dermis of the skin. These cells are like water balloons full of fatty molecules called leukotrienes and prostaglandins A & B. When a needle is inserted into the skin, it pops the mast cells and releases the leukotrienes and prostaglandins. Prostaglandins cause the cutaneous nerve in the area to fire (which activates the process described in the previous paragraphs). Leukotrienes are the strongest anti-inflammatory substance the body can produce.
Leukotrienes cause local capillaries to vasodilate and become permeable. White blood cells called macrophages leak out through the capillaries and immediately begin to heal the damage caused by the needle stick.
However, the healing caused by the needle insertion isn’t limited to the damage caused by the needle. If there is other damage in the area from previous traumas or injuries, that will also be addressed by the immune chemicals released by the needle insertion.
What’s more, the micro-trauma caused by the needle starts a systemic immune response. This promotes healing of the soft tissue throughout the body – not just at the needling site. After the needles are removed, the needle-induced lesions continue to stimulate the body until the lesions heal. This means that the anti-inflammatory effect of acupuncture persists for 2-3 days (and sometimes as long as a week) after the needle is withdrawn.
Genetically the body is not designed to be in chronic pain. It will do everything it can to get us out of pain. Acupuncture “reminds” the body how it should be functioning, and helps its powerful inbuilt pain relieving mechanisms kick into gear. It’s a bit like jump starting a car. You’re not changing how the car works, or even adding anything to the engine. You’re just giving the battery a little jolt so the car can run how it’s supposed to.
It’s important to understand that this neurochemical mechanism not only provides pain relief, but also promotes homeostasis and tissue healing and regulates the immune, endocrine, cardiovascular and digestive systems. This explains why getting acupuncture treatment for your knee pain also addresses other problems you might have, such as asthma, irritable bowel, high blood pressure, anxiety and insomnia.
In the next and final article of this series, I’ll explain the advantages of Chinese medicine over western medicine for the prevention and treatment of most common health conditions.
Recommended resources for more information
- Biomedical Acupuncture for Pain Management, by Yun-Tao Ma, Mila Ma & Zang Hee Cho
- The Dao of Chinese Medicine, by Donald Kendall
- The Biology of Acupuncture, by George Ulett & Songping Han
- The Neuroimmune Basis of Anti-inflammatory Acupuncture, by Ben Kavoussi & Evan Ross
- Acupuncture in Medicine Journal (part of British Medical Journal)
- Pomeranz B. Acupuncture analgesia – basic research. In Stux G, Hammerschlag R, editors: Clinical acupuncture scientific basis. Berlin 2001. Springer.