(Workbook Page 28)
The brain-body loop describes the constant connection between body and brain. Where pain is concerned it involves both the suppression of acute pain and amplification of persistent pain. It is a two way communication between the Connective Tissue System and the Nervous System.
In acute pain, the nerve cells pain processing regions of the brain fire due to input from peripheral tissue. Some of these nerve cells send signals to the spinal cord to suppress the incoming signal. There is no pain when the injured tissue is at rest. Pain is re-experienced if a person stresses the injured tissue. Higher functioning regions of the brain send signals to stop the pain and return the tissue to healing. Inflammation in the peripheral tissue gradually stops and is replaced by an anti-inflammatory response. Growth factors are released to repair the extracellular matrix and local nerve endings. Once this occurs, pain signals to the brain desist. Use of that tissue returns to normal and painless function.
The brain-body loop works quite differently when the pain becomes persistent
Chronic inflammatory processes begin in the same manner as acute inflammation, but several factors lead to long term potentiation in nerve cells in the pain pathway in the brain. As a result a glial cell (Astrocytes and microglia) inflammatory process is initiated leading to creation of more Substance-P in persistently firing nerve cells .This, in turn, causes the pain map to expand in the brain and release of Substance-P and several other inflammatory products into the injured tissue, overwhelming the anti-inflammatory response. This establishes a loop between brain and body that perpetuates the experience of pain, while preventing proper healing.
Signals coming in from the peripheral nervous system increase in the central nervous system. This is known as wind-up. A series of events occur leading to runaway firing of nerves with or without input from the part of the body that is injured. The brain tries to suppress the signal, but it is too powerful. Brain astrocytes release inflammatory molecules. Nerve cells release more of the main pain neurotransmitter, Substance-P. Higher levels of Substance-P expand the network of pain transmitting nerves. Higher functioning areas of the brain signal to stop using that part of the body, regardless of its state of repair. Inactivity and disuse lead to loss of function and local release of more inflammatory chemicals. Substance-P is sent out to the peripheral tissues, functioning as an inflammatory substance. Local anti-inflammatory responses are overwhelmed. This results in ongoing inflammation, increased pain signals to the brain and augmentation of the brain-body loop.