Acute pain - which is a sudden onset of brief duration, may be caused by an infection, accident or surgery. Chronic pain which may be the result of a specific condition, does not diminish with treatment and does not go away with the passage of time. An understanding of how pain happens is basic to finding more effective ways in dealing with it. There are millions of sensory receptors on the surface of the body and in it that keeps the brain informed about temperature, condition of organs, unusual changes and so forth. These receptors and the brain communicate in a complicated code through a network of nerves located throughout the body.
Every nerve consists of bundles of fibers which can be categorized as large and small bundles.
The large bundles carry impulses related to touch. The small bundles send messages slower than the large ones and carry pain the pain impulses. Both sets of bundles meet at the spinal cord. Scientists believe that there is a gate-like mechanism in the spinal cord that can shut against pain messages. Relief associated with electrical stimulation or acupuncture may be the result of the pain gate being closed by using these methods.