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The Pain Is In Your Brain

There is an extremely important relationship between the brain, the IML (intermediate lateral cell nucleus of the spinal cord), and motor activity (activity that allows us to move in regards to chronic pain syndromes). The intermediate lateral cell nucleus, or IML, of the spinal cord drives the sympathetic nervous system. Increasing the sympathetic tone increases the release of norepinephrine and catecholamines through stimulation of the adrenal medulla. When all of this occurs, the nociceptive afferent fibers, or pain fibers, are bathed in norepinephrine.

When nociceptive afferents are bathed in norepinephrine, secondary to increase sympathetic output, there is an increase in the expression of the alpha 1 adrenergic receptors which are linked to sodium channels and cause excitation. Thus, there is an increase in the IML, or intermediate lateral cell nucleus. The increase in the IML output causes an increase in the release of norepinephrine, which when released causes an upregulation in the uncovering of the alpha 1 adrenergic receptors along the membrane of the C fiber, or pain fiber. Usually, the C fiber is covered, but in the presence of norepinephrine, the cover is removed. As brain function decreases, IML function will increase and therefore increase the probability of pain. As brain function increases, IML function will decrease.

This will decrease the release of norepinephrine and decrease the probability of pain. Usually, if a person were to exceed metabolic capacity, or over-stimulate his bodily functions (such as running a marathon or lifting weights for the first time in years), he would expect to feel some muscle pain. But what about the person with chronic pain, whose pain just came on gradually with no known cause? Let me give you an example. There is nothing physically wrong with a person's leg, yet he may feel pain in his leg as a result of alpha adgernernic activation due to high firing of the intermediate lateral cell nucleus because the nociceptive afferent would fire spontaneously.

© 2005 Michael L. Johnson, D.C., D.A.C.N.B.

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