Pain Signals to the Brain from the Spine How these Work
Did you know pain messages travel along the peripheral nervous system till the time they reach the spinal cord? According to the gate control theory (a scientific theory about the psychological perception of pain), there are “gates” on the bundle of nerve fibers in the spinal cord located between the brain and peripheral nerves. Messages of flow of pain from the peripheral nerves to the brain are controlled by these spinal nerve gates.
A number of factors determine the management of pain signals by spinal nerve gates. These include:
- Pain message intensity
- Competition from other incoming nerve messages such as vibration, touch, heat, etc.
- Signals from the brain instructing spinal cord to increase or decrease pain signal priority.
The message may be handled in the following stated ways depending on the way gate processs signal:
- Allowed to enter directly to the brain
- Modified before being forwarded to the brain (example, influenced by expectations)
- Prevented from reaching the brain (hypnosis-induced anesthesia)
Complexity of the process is illustrated by the “phantom limb” phenomenon (a phantom limb is the sensation that an amputated or missing limb is still attached). Here, the gate control theory supplies a framework to explain this through a complex interaction of the structures of the nervous system.
Many things happen the moment pain signal reaches the brain. Some parts of the brain stem (which connects the brain to the spinal cord) may suppress or wrap incoming pain signals. This is done by producing endorphins (morphine-like substances occurring naturally in the body).
Production of endorphins is triggering some of the following major factors:
- Vigorous exercise
Athletes do not feel pain from a serious injury until the game is over. Such is the impact of endorphins! No wonder low-impact aerobic exercise (such as riding a stationary bike) are recommended as an excellent method to help control chronic back pain.
Pain messages may also be allowed to travel along different pathways in the brain:
Faster Pathway – A “fast” pain message such as A-delta fiber is relayed by the spinal cord towards certain locations in the brain (cerebral cortex and thalamus). The cortex is the part of the brain where all of the higher thinking takes place. So when fast pain message reaches the cortex, it prompts instant action to decrease pain or threat of injury.
Slower Pathway – Chronic pain has a tendency to move along a “slow” pathway (C-fiber). Slow pain is perceived as dull, burning, aching, and cramping. The slow pain messages travel along the same pathways as the fast pain signals through the spinal cord. However, the messages take route to hypothalamus and limbic system as soon they reach the brain. The hypothalamus releases specific stress hormones in the body. The limbic system is responsible for processing emotions. No wonder chronic back pain is mainly associated with depression, stress, and anxiety. Slow pain signals pass through brain areas that control these emotions and experiences.
The brain is also capable of controlling pain messages via attaching significance to personal and social context in which pain is experienced by an individual. The process occurs in the cortex. One of the classic examples is that of soldiers who show less pain despite getting seriously wounded in combat than wounded civilians involved in accidents. Significance added to the situation makes all the difference!