How the Nerves and Brain Communicate to Create or Ignore Pain Messages

The pain alert system in the body is one of the most useful aspects of the nervous system, at least from a survival and danger-avoidance standpoint. But when the system becomes overly sensitized, either due to tissue damage or long-term inflammation, it can cause all sorts of problems for people, the main one being chronic pain lasting months or years. But much of the pain that is felt years after an injury may be due to the nervous system and brain not communicating effectively with each other anymore.

There are pain sensors spread throughout the body; they are located near the skin, in muscles, and on bones. When these nerves receive enough of an input, they open up and allow a flood of positively-charged ions in, which sends a pain message to the spinal cord and brain. The pain receptors can be activated through a number of different mechanisms, from a hammer hitting someone's thumb, to a dangerous chemical being dropped on a hand or leg, to hot coffee being spilled. All of these can result in pain due to mechanical, chemical, or temperature changes that affect the nerves.

However, the pain messages must reach a critical level in order to send a real pain message to the brain. Lightly touching a hammer to your thumb will not usually send you screaming and sucking it to reduce the pain (unless the nerves are already highly sensitized). The pain receptors may open and allow some positive ions in, but they are not judged to be enough to create pain. The brain, along with the spinal cord, evaluates the messages received from the pain receptors and decides whether or not there is a danger. If danger is perceived, then pain is the result, but if the inputs are not sufficient to cause pain, the brain does not send the message to protect the body part.

This processing by the brain is one of the most important aspects of pain for people to understand. Elite athletes may be able to run the last 6 miles of a marathon with a stress fracture, while other people have to take the day off of work if they have a mild paper cut. Why is this? In essence, it is due to the sensory messages that the brain receives from the tissues and the messages it sends after receiving those inputs from the nerves. The actual condition of the tissues is one of the aspects the brain evaluates, but it is not the only one. It may be more important to keep running and finish the race than to send a danger message full of pain.

But when the brain believes that a person is in danger, it will send the pain message. At that point, the brain is almost completely in control and other various systems can take over. There is nothing like being hit with an object to test the reflexes to see how fast a person can get out of the way. The inflammatory system may turn on as the body then sends blood and nutrients to the site of the injury to cause swelling in order to protect the tissues. And pain from an acute injury can last as long as the brain determines that there is still a danger.