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Posted on 08-29-2017
To understand pain, you must first understand how the cells of the nervous system transmit the pain signal. If you were to put a nerve cell underneath a microscope, you’d see little tendrils that look like roots projecting from one end of the cell body. These are called dendrites. At the other end of the cell you’d see a long, thin, almost cord-like structure called an axon. Nerve cells are linked by means of these axons and dendrites. Not through actual contact, though— the transmission of information from nerve cell to nerve cell is much more miraculous than that. As I’ll explain below, nerve cell information is transmitted in the form of electro-chemical impulses and neurotransmitters.
You have nerves extending through almost every single inch of your body. There are nerve cells where you’d expect them— in your toes, fingers, teeth, tongue, and so on— and a few places you wouldn’t— such as the heart, liver, lungs, and intestines. Some of our nerves, like the ones that go to our skin, are designed to provide sensory information, such as temperature, pain, and pressure, to the brain. Other nerves, like the ones that go to the muscles and joints, are linked to our experience of what’s called proprioception, or our sense of physical movement. (In truth, most of the nervous system is used not for sensation but for motor activity, and for making tissues and organs function properly.) Almost all of our nerve cells are linked in a system or network of interconnectivity that leads from every part of the body to the spinal cord and from there to the brain. Information from your nerves is processed and responded to within the spinal cord and brain (also known as the central nervous system).
The sensory experience we call pain occurs when nerve cells that are specifically designed to send sensory messages become irritated in a particular way. The message of pain travels to the spinal cord, through a kind of biological junction box, and then to the brain, where we actually interpret the message. Anyone who’s in pain may find this hard to believe, but feeling pain is just a small portion of the brain’s activity, comprising only 6 percent of the functioning of the entire nervous system.
Let’s say you’re out walking or Rollerblading, and all of a sudden you trip and skin your knee. In that moment, hundreds of biological events occur throughout your body. But what’s happening with your nerves? As soon as your knee hits the concrete, the nerve cells in your skin (the organ in the body with the most widespread dispersal of nerve cells) react by sending impulses through their axons. The message travels to the very end of the axons, which then release chemicals called neurotransmitters. The neurotransmitters carry the information from the axon of one cell to the dendrites of the other, across gaps called synapses. The dendrites have receptors on their root-like ends specifically designed to receive these neurotransmitters. Once the dendrites get the message, so to speak, they send it along to the axon at the other end of the cell, and the chain of communication continues. (Of course, all this happens almost instantaneously.)
Depending on the stimulus being provided to the nerve cell, different kinds of neurotransmitters are produced, and they stimulate specific kinds of nerve fibers. For example, the fibers excited by the pain in your skinned knee are nociceptors. They are what we call class C nerves, which are the smaller, more primitive chains of nerve cells. (These nerves appeared first in the evolutionary development of multicelled creatures, indicating that the ability to experience pain has been an important survival priority for most life forms from the very beginning. There are also class A or B nerves, which are thicker and communicate much faster.) Nociceptors react to several different kinds of pain or stimulation— everything from a pinprick to heat to pressure. When the nociceptors are stimulated by pain, they release a chemical known as substance P (P for pain), along with several other neurotransmitters. Substance P then carries the message of pain from nerve cell to nerve cell, through the dendrites and axons, until the message reaches the dorsal horn, the part of the spinal cord that’s in charge of receiving data from all the sensory nerves. From the dorsal horn the injury information is relayed to the thalamus, a structure deep in the brain that’s responsible for receiving sensory data and sending it on to the cortex. The arrival of substance P in the thalamus gives the brain the message, “Help! You’ve got pain!” so the brain can tell the body to do something about it. Then back the message goes: from the brain to the spinal cord (through a different area of the spinal cord devoted to sending messages from the brain to the body), to the nerves that branch off in the direction of the knee, all the way down to the area that was damaged when you fell. At that site, different neurotransmitters and chemicals are released that help protect the body from further injury. The knee starts to bleed and perhaps swell. The area becomes tender to the touch, and substance P continues to be emitted whenever the skin is bumped. A complex feedback loop has been established between the hurt knee and the brain, to help protect the body from having any further damage done to it.
To discover more about how our nerves work, check out Dr. Lenarz’s book The Chiropractic Way, available on Amazon.
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