Pain is defined in the literature as - An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.
What is important to note here is that the emotional experience is a very important component of the pain experience and that tissue damage is not necessary to create pain. Sometimes the threat of damage or the unpleasantness of the emotions and thoughts associated with the experience can create or amplify pain. This explains why sometimes it can be hard to “find” the pain with an x-ray or an MRI.
Where does pain come from?
Pain is a very complex experience that can be difficult to describe, define, and manage. Everyone will experience it differently, no two injuries or illnesses will be exactly the same. Something to consider is that if a pain has become chronic or persistent is that the pain itself is often no longer directly related to the level of tissue damage. The tissues are only a part of the story and to understand the sensations that our brain has to interpret, we need to discuss the nerves as well.
Nerve cells (Nociceptors) - What is important to know is that while the tissues and nerves in our body provide the information required to register pain, that the pain itself does not live in those tissues. The nerve endings or nociceptors report to the brain about what they are sensing in the environment by sending electrical signals. While many nociceptors have the capacity to register multiple things, such as cold, heat, pressure, or chemical changes, they are specialized to their favourite thing. Once enough stimulus is presented to a nociceptor it will fire a burst of electricity, called an action potential, up to the spinal cord and eventually the brain. The processing power of the brain is brought to bear and it makes the decision about what this information means. In a majority of cases, this is dependent on what the brain decides to be true.
For example, if you have ever had a bruise or a papercut and not noticed it until you looked at it, you understand that it is not always completely clear when our brain decides to bring something to our attention and create a pain experience.
It is certainly not black and white how the brain decides what to pay attention to and to decide what is painful. There are many factors at play, such as environment, emotion, fatigue, stress, context, and memory. Because neurons get stronger and stronger in their connections the more that they are used, an uncomfortable and frequent stimulus can make it easier for the brain to feel certain things. When these nerves (nociceptors) are exposed to injury or inflammation, they become more easily stimulated by their environment, meaning that it takes less pressure, or heat, or cold for them to send a burst of electricity to the brain. This can mean a couple of different things. Either the nerves will report more and more signal to the brain, overwhelming the systems that are in place, or the nerves will start to report on things that really aren’t that important. Imagine if you got a notification on your phone every time a seed from a dandelion was blown off by the wind. You would get pretty tired of it after the first few hundred or so. In the same way, these never-ending signals from the nerves make the brain hypervigilant and irritable. When this happens there can be a decrease in the ability of the brain to make sound decisions about the pain experience.
Inflammation - The initial kind of pain that is typically experienced has to do with the properties of tissue damage and inflammation. Inflammation is a natural process that the body undergoes after injury. The body brings immune cells and their accompanying chemicals to an area to clean up the damaged tissue and to remove anything that is dysfunctional or potentially disruptive to the normal function of the tissues.
A side-effect of inflammation is one that most people are familiar with, swelling. The increased concentration of certain chemicals and molecules also brings with it an excess of fluid. This can complicate some matters as swelling will change the pressure on the surrounding tissues, hampering their function. It can also lead to stiffness in joints and tissues as they cannot move as freely in the presence of the extra fluid.
The second side effect is one of sensitivity. In the presence of inflammation, the nerve endings in our tissues are more easily provoked to produce electricity that travels to the brain. Much like a room full of normally clapping people can fill an auditorium, a collection of very quiet pressures can create a roar in a nerve when it is inflammed or more sensitive. This extra electricity is sent to the brain and the first response is typically to be guarded and cautious of this new information. Remember, that in a normal environment an increase in electricity quickly or sharply is typically a sign of danger or harm. This gets a bit confusing when the tissues in question have become more sensitive because the amount of electricity that they produce is not necessarily tied to the experience that the body is having in that moment. For example, after a sunburn, the skin is more sensitive to touch and heat as those nerve endings and the surrounding tissues have become injured and sensitized.
Secondary Pain (Hyperalgesia) - This is the concept that tissues and body parts not associated with the original injury or pain experience can become sensitive or irritable enough to express themselves with normal day to day activities and pressures. For example, if a sore knee becomes a sore knee and shin, followed closely by a sore ankle as well. Since these tissues share many connections through the nervous system and are processed by a similar part of the brain, the overlap becomes increasingly easy as the pain experience continues.
So what can we do about it?
The good news is that the nervous system, including the nerves in our tissues and the cells in our brain are highly capable of change at every point in our lives. Our brain exerts a great deal of influence over the interpretation of the signals in our body. This means that our thoughts, emotions, and previous experiences mean a great deal when it comes to the idea of persistent pain.
Education itself, knowing more about what is happening in our bodies and what it means is a powerful tool in creating an environment in which the brain and the nerves can change and become more in tune with the environment and the demands being placed upon them. Once the brain is on board, another piece of the puzzle is to work with the tissues themselves so that they can learn not to scream at the brain every time they encounter a stimulus. This can be done in a number of different ways, from hands on therapy for joints and muscles, therapeutic exercise, and potentially the use of other interventions such as acupuncture/dry needling and massage.
This is a very basic beginning to what is a broad and complex topic, but I am excited to expand this material and share these concepts with anyone who may benefit from education and intervention. If there are any questions about what you have read today, please feel free to leave a comment or reach out to our office directly.
- Trent, PT
- Modern pain neuroscience in clinical practice: applied to post-cancer, paediatric and sports-related pain. Malfliet, A. et al. 2017. Brazilian Journal of Physical Therapy.
- Neuroplasticity of Supraspinal Structures Associated with Pathological Pain. Boadas-Vaello, P., et al. The Anatomical Record 2017.
- The role of calcitonin gene-related peptide in peripheral and central pain mechanisms including migraine. Lyengar, S., Osispov, H., Johnson, K. Pain. April 2017.
- Cellular and Molecular Mechanisms of Pain. Basbaum, A. et al. October 2009. Cell.
- The Cell and Molecular Basis of Mechanical, Cold, and Inflammatory Pain. Abrahamsen, B. et al. Science. August 2008.
- http://www.iasp-pain.org/Education/Content.aspx?ItemNumber=1698#Pain. Retrieved Nov 13, 2018.