If I am not moving energy, what am I accomplishing when I insert an acupuncture needle into your dog or cat?
Let’s get a little science-y!
When you look at the anatomy underneath and around acupuncture points, you’ll find many are associated with a nerve in some way. The most common anatomical features of acupuncture points include:
- Nerve emerging from bone
- A larger nerve splits (bifurcates) into smaller nerves
- Nerves bundles associated with blood vessels (nervi vasorum)
- Insertions of a motor nerve into muscle
- Locations containing a combination of both sensory and motor neurons
- A deeper nerve becoming more superficial
Other acupuncture points may not align with easily identifiable nerves, but have other connective tissue features in common:
- Many channels along the skull follow cranial sutures – where the bones are fused
- Connective tissue, such as tendons, ligaments, and joint capsules, are full of nerve receptors, and these make great acupuncture points despite not having a larger named nerve to stimulate
- Trigger points – muscles and fascia that become tender or knotted up – these often coincide with acupuncture points
When the Chinese were figuring out these points and channels, they did not know about the underlying nerves and anatomic structures, yet they figured it out indirectly through the “mapping” of acupuncture channels. I find that quite impressive!
So when we put an acupuncture needle into the skin at one of these points, what happens? The needle is stimulating mechanoreceptors in the tissue. These are special types of cells which are responsible for noticing things like pressure, temperature, stretch… acupuncture needles. Notice these receptors do not detect pain – those are a different type, called nociceptors. Our goal is to stimulate only mechanoreceptors, and not stimulate nociceptors, resulting in positive effects of acupuncture but not pain. (Occasionally some nociceptors may be stimulated as well, and if the animal is uncomfortable, we’ll take those needles out.)
These mechanoreceptors are each attached to a neuron, which branches off a nerve that ultimately connects with other nerves. Let’s diverge a second and review nervous system 101.
The term “nervous system” refers to basically all the nerves in the body. We can divide it into 2 broad categories: the Central Nervous System (CNS) which is the nerves in the brain and spinal cord, and the Peripheral Nervous System (PNS) which is basically the nerves in the rest of the body. We can divide the nerves in the PNS into two categories: Somatic and Autonomic. The Somatic nervous system includes those nerves that are voluntary, meaning we can control them, so it’s a lot of nerves supplying muscles. The Autonomic (sounds a lot like automatic) nervous system is involuntary – the actions we cannot control, but keep us alive.
Stay with me – almost done! The Autonomic (or automatic) nervous system is divided into two categories, and these are the ones I will be talking about. The Sympathetic nervous system is what is responsible for “fight or flight.” It’s how we lift cars off babies (in extreme situations) but it also can become over-active with any chronic disease. The body is trying to be helpful, but it’s counter productive. The Parasympathetic nervous system is the mellow one. It maintains the day-to-day functions of the body. If the sympathetic nerves give you “fight or flight”, the parasympathetic nerves tell you to “rest and digest.” It is important for both of these systems to be in homeostasis, or balance, over the long term, in order to be healthy.
With many disease or pain processes, we have a chronic, low-level over-stimulation of the sympathetic nervous system, and we’d like to use acupuncture to tell it to calm down. Conversely, sometimes the parasympathetic nervous system is “asleep at the wheel” and we’ll want to wake it up. Either way, we can think of it is “restoring our factory settings.”
Back to acupuncture needles! We have a needle in the skin, and those mechanoreceptors are wide awake, sending the signal up the nerve. The message travels up the nerve to the spinal cord. Once it reaches the spinal cord, it can then travel to the brain. But how does a needle in a leg or foot affect something as unrelated as the digestive tract? Or how does a needle on the front leg affect the face? We need a place where these neurons can all intercommunicate. The technical term is a “somato-autonomic convergence center,” which describes it pretty well. “Somato” refers to the physical body (skin, muscles, etc) and “Autonomic” refers to the autonomic nervous system (sympathetic vs parasympathetic) we’ve been talking about.
It turns out we have just that kind of center! There is a section of the brainstem called the nucleus tractus solitarius (NTS). We can think of it as a “Grand central station” for nerves, since many nerves from a variety of sources end up passing through this region. Some of the nerves passing through the NTS are the Trigeminal nerve (Cranial nerve V), which communicates sensation from the face; Glossopharyngeal nerve (Cranial nerve IX), which carries signals from the carotid body (regarding blood oxygen levels and blood pressure) as well as sensation from the ears; and a variety of spinal nerves, which carry signals from the rest of the body (limbs, skin, etc). When these nerves are all in this tiny space, they can easily communicate with each other. This column of neurons is also very close and able to communicate with the dorsal motor nucleus of the Vagus nerve. This is big.
The Vagus nerve (Cranial nerve X) is the main parasympathetic controller for the internal organs. This one nerve has a lot of jobs:
- Sensory – communicates signals from the following regions to the brain: throat (larynx, pharynx), esophagus, trachea, aorta, and much of the abdominal viscera (organs like stomach, intestines, kidneys, liver, etc).
- Motor – send signals from the brain regarding movement or function to: the muscles of the throat, and the smooth muscles and glands of the thoracic (chest) and abdominal viscera (organs).
So we know the vagus nerve has a lot of responsibilities. And we know where part of it hangs out (in the NTS). So to communicate with the vagus nerve (and therefore the parasympathetic nervous system) we can use acupuncture needles to stimulate nerves at other parts of the body that have connections through the NTS. This is how a point in the leg can communicate with the stomach.
What if we want to communicate with the sympathetic nervous system? Sympathetics are primarily based in the intermediolateral grey column of spinal cord, which starts just below the neck and ends near the lower back. These nerves branch off the spinal cord between each vertebral body (back bone). So yes, there are many of them, and they are spaced at regular intervals all the way down the back. So if we want to communicate with the sympathetic nerves going to a certain region, we might choose acupuncture points along the back. If we want to communicate with the parasympathetic nervous system, we’ll have two choices. We can use points that communicate via the NTS, or, if it’s the back end of the animal we are treating, we can use some of the parasympathetic nerves I haven’t mentioned yet that come off the spine down near the sacrum (pelvis).
When we are using acupuncture needles to communicate with the autonomic nervous system, we aren’t only talking to one side and completely ignoring the other, the sympathetic or the parasympathetic. We’re talking to both. Even though there may be primarily sympathetic or parasympathetic nerves or connections at an acupuncture point, there is a never exclusively ONE nerve type. Think of it as a room full of small children. Some are playing nicely, or reading, or otherwise being good kids. There’s a couple that are misbehaving -let’s use playing with a lighter, for example. If you open the door to the room and say “What are you up to?” the kids who are behaving will likely keep playing as they were with a casual “I’m reading” or “I’m playing” while the kids playing with the lighter will immediately stop and probably respond with “Nothing!” The acupuncture needle is the adult walking into the room. The behaving system (usually the parasympathetic but not always) is not affected and keeps doing what it was doing. The sympathetic realizes it is too wound up (puts down the lighter), and starts the journey towards its neutral, default state.
How does acupuncture treat pain, specifically?
Acupuncture does more than manage the general sympathetic/parasympathetic balance – it can do a lot for pain using different mechanisms! Turns out mechanoreceptors are quite multi-talented.
Once the mechanoreceptors are stimulated by the needle, they send a message to the dorsal horn of the spinal cord. There are many types of neurons in this region of the spinal cord, and among them are fibers that relay pain sensations, called A-delta and C-fibers. Stimulating the mechanoreceptor increases nerve firing in the dorsal horn, and quiets these fibers down, reducing the sensation of pain. Furthermore, the signal from the needle travels up the spinal cord, through the spinothalamic pathway to reach the thalamus in the brain. The brain releases endogenous opioids (pain relieving chemicals produced by the body itself), such as B-endorphin. Conversely, as the processed signal travels back down the brainstem toward the spinal cord, other parts of the brain (such as the nucleus raphe and locus ceruleus, in the brainstem) release pain-killing chemicals like serotonin and norepinephrine.
The following review article spells out the details of the various mechanisms of action for acupuncture to reduce pain. It’s a long read, but an interesting one! https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3947586/
This statement from the above article says it nice and concisely: “Electroacupuncture increases opioids at inflammatory sites via two pathways. 1) It activates sympathetic nerve fibers to enhance migration of opioid-containing cells to the site. 2) It triggers hypothalamus-pituitary-adrenal [axis] to decrease COX-2, which in turn interfere with endocannabinoid metabolism, leading to increased levels of opioids at the site.”
Finally, acupuncture can stimulate portions of the brain through yet-to-be-determined mechanisms. There are many fMRI studies out there of acupuncture and brain activity, but we need more research. Here’s a good summary of the current data (paper is 5 years old, but still good): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3322129/
So I hope this little bit of science didn’t scare you off. And if you didn’t understand all of it, don’t sweat it! My goal was to simply explain some of the “behind the scenes” ways acupuncture works. We are not moving energy, but we’re talking with the body, reminding it to help heal itself.