PAIN BASICS
A pain experience is triggered by a noxious stimulus caused by an injury, illness, surgery or unknown trigger that results in the activation of specialized nerve endings called nociceptors. The cell bodies of these nociceptors (first-order) neurons are located outside the Spinal Cord.
Activation of these nociceptors triggers a cascade of incoming impulses that travel to the spinal cord along both myelinated (Aβ) and unmyelinated I nerve fibers. These fibers enter the spine almost exclusively through the dorsal root, and synapse (second-order) in the dorsal horn of the spinal cord, where they move to higher levels such as the thalamus, hypothalamus, reticular system and cortex of the brain.
It is these higher-level sites that bring the complex emotional feelings, (thalamus and limbic system), alterations in sleep pattern (reticular system and hypothalamus) and stress or survival response (hypothalamus) that pain may evoke. These higher levels trigger biological processes that can then amplify or inhibit the pain signal that the brain will ultimately interpret.
As tissue heals, pain signaling should weaken and eventually shut-off.
However, if the threat or perception of harm continues, the structure and function of the nervous system continues to be shaped and re-shaped through plasticity altering the accuracy and intensity of information sent back to the brain.
This plasticity or neuroplasticity as it is often referred to, is fundamental to our understanding of both the persistence of pain in some pain syndromes and the mechanisms of action of the different pain treatment modalities.
The intensity of pain regardless of its duration or mechanism, is influenced by many factors that can have a positive or negative impact on how pain is experienced. For example, factors such as physical, emotional, social, and spiritual components all contribute.
This multidimensional feature of pain is often referred to as “total pain”, which is a term coined by Dame Ciecely Saunders who was the founder of the hospice movement in the 1960’s.
This has also been referred to as the Biopsychosocial model of pain which describes the fusion of psychological and social factors interact with brain processes to influence an individualswell being.
Using this approach; pain and disability can be described as a multidimensional dynamic interplay of physiological, psychological, and social factors that influence each other.
In other words, ITS COMPLICATED.
What matters however is our understanding how each component contributes to pain and suffering can help us better recognize and address the patient’s needs.
PAIN HAS PURPOSE!!
The biological processes within our pain system act like an alarm to warn us of potential harm. These processes are linked to our fight, flight or freeze response which is a physiological reaction located in the Amygdala, or primitive brain in response to a real or perceived threat. Our ability to pay attention to pain and respond with purpose is essential for human survival.
When activated, these complex biological processes have the ability to alter pain signalling within the central and peripheral nervous system based on information rapidly gathered from higher-level sites within the brain.
As tissue heals, pain intensity should diminish. However, for 1 in 5 Canadians pain signalling continues to send out a distress call. This pain is often referred to as complex or persistent pain and usually indicates that the illness, injury, surgery or unknown trigger that contributed to the pain experience, has produced changes in the efferent nociceptive neurons that conduct pain information to the brain called sensitization.
This contributes to a “wind-up” effect within the CNS perpetuating pain long after tissue has healed.
Factors that drive the “chronicity” of chronic pain which can best be described as an imbalance between pain amplification and pain inhibition includes:
- Central sensitization
- Neuroinflammation: Glia cells
- Pain Protective Behaviours {(Muscle memory, movement memory (Pain protective stance)}
- Brain memory
- TheMessenger: (Amygdala and alarm chemistry).
At their core central sensitization, muscle memory, movement memory and brain memory are ultimately about survival and protection.