Nerve Mechanics Part I
Nerve mechanics, or neurodynamics simply means the study of the mechanical properties of nerves - how they stretch, move, glide, and cause pain as the body moves. Science has made some exciting leaps forward in this area in the last twenty years,and these have been well summarized in some great books by Michael Shacklock and David Butler. Amazingly, this work is unknown to many doctors and physical therapists. This is unfortunate because nerve mechanics are easily understandable and help explain and treat a great many painful conditions. Here are some basic facts that will give you a lot of insight.
Nerves are built for movement
The picture to the right shows the major nerves of the body. As you move around, those nerves need to slide, bend, elongate and withstand compression to allow the movement. Fortunately, they are very well adapted for this task.
Notice the nerves that run from the neck to the tips of the fingers on the radioactive man. When he bends his elbow, his ulnar nerve needs to bend around the point of his elbow, which causes it to compress and flatten out. If he tilts his head to his left shoulder, you can see that this would pull on his nerves from above, causing them to slide upwards past any stationary adjacent bones or other physical structures. He could pull on the nerves from below and slide them downwards by reaching his arm down and out while extending his wrist and fingers backwards. What if he applied tension from both ends at the same time? The nerves would simply have to elongate. It does this by stretching just like a bungee cord, and in the process grows thinner.
Nerve tension is a body-wide phenomenon
A key point to note is that nerves cross many joints, and therefore movements that cause tension or relaxation of the nerve at one joint can cause tension or relaxation of the nerve at a distant joint or vice versa. For example, by looking at the picture, you can see that the spinal cord goes from the top of the neck to the low back and then splits into the two sciatic nerves which run down the back of the legs and then turn into the common peroneal nerves which end in the feet. There is a continuous line of pull from the top to the bottom and tension or slack at one end can be sensed at the other.
You can feel this easily by moving into a forward bend to touch your toes while moving your head and neck to stare at your navel. When you go low enough, you will feel a familiar intense stretch at the back of the knee. This is the sciatic nerve saying stretch no further (no it's not the hamstrings as most people think.) You can greatly reduce the intensity of the feeling in the back of the legs by lifting your neck to look up. This releases tension on the spinal cord from above and the resulting slack eases the tension on the sciatic nerve. Move your head back and forth to feel how the neck position affects the feeling at the back of your knee. It should be pretty obvious if you're doing it right. The point here is that your whole body is connected. A lack of neural mobility in the neck can easily affect the low back or even the hamstring or vice versa. The converse is also true. You can reduce pain in one area by improving mobility in another.
Movement of the nerves is healthy
The movements of the nerves - bending, sliding, compressing and stretching - are completely normal and healthy under normal circumstances. In fact, proper nerve function depends on movement – alternating tension, compression and relaxation probably assists circulation and reduces the nerve's inner viscosity. In other words, motion is lotion for the nerves just as it is for all the other parts of the body. However, as you might have guessed, once the nerves become sensitive, moving then can cause pain. In fact, a great many painful conditions that you may have thought were caused by a sore muscle or tendon such as carpal tunnel, plantar fasciitis, tendonitis, a pulled hamstring etc, may actually be caused by sensitive, compressed or inflamed nerves.
In the next post I'll discuss how nerves become sensitive to movement.