Pain Mechanism


“Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

Our nervous system is the most complex organs in our body.  Because of this pain is very complex.

Throughout our bodies are pain receptors, called nociceptors.  These receptors are stimulated due to release of various chemicals by damaged tissue such as histamine, substance P, serotonin, bradykinin and prostaglandins.  When stimulated, the nociceptors release of various chemicals by the damaged cells including histamine, substance P, serotonin (5HT), bradykinin and prostaglandins.transmit the pain signal along sensory nerves to the spinal cord.  In the spinal cord the impulses are processed by the dorsal horn and sent to the brain.  Sometimes signals sent to the spinal cord communicate directly with motor nerves, to cause for example ones arm to quickly withdraw after touching a hot plate.  This is called an automatic reflex and does not involve the brain or conscious thought.  Most of the times pain signals are sent upwards in the spinal cord from the dorsal horn via ascending nociceptive tracts, such as the Spinothalamic tract.  These tracts terminate in the medulla, midbrain and thalamus.  Further processing in the thalamus leads to signals being sent to areas in the brain that control things such as heart rate, blood pressure and emotions.  Thalamic neurons also project to regions of the cortex including the somatosensory cortex, were fine discrimination of pain occurs.

We experience pain everyday when we get a paper cut, stub our toes or hit our funny bone.

You may not want to believe it but pain is a protective mechanism.  It tells us to pull away from a potentially damaging situation, like a hot pan.  It warns us to take it easy and thus protects a damaged body part while it heals.

Most of the time pain goes away once we remove the stimulus.  Unfortunately sometimes pain persists despite removal of the stimulus.  Other times pain starts in the absence of any detectable injury or stimulus.  When pain last for prolonged periods of time and is uncontrolled it can start having a more devastating effect on ones quality of life that is far more destructive than the discomfort of the pain itself.

But what is the difference in acute and chronic pain?

Often acute pain has a sudden onset and is usually sharp in nature but can have other forms.  It can be mild or severe in intensity and last a few seconds to months.  Most of the time acute pain last less than 3 months and usually goes away once the underlying cause is treated or heals.  When acute pain last longer than 3 months it is often considered chronic pain at this point.

Chronic pain often persists besides the fact that there is no longer an identifiable stimulus.  Pain signals in the nervous system remain active, and these effects can lead to both physical and emotional manifestations.  Physically one can feel nausea, fatigue, muscle aches, decreased energy, and insomnia, among other things.  Emotionally people can experience wide mood swings, depression, anger, anxiety, and a sense of being overwhelmed.  These physical and emotion changes soon start affecting one’s ability to work, enjoy life, and perform activities of daily living.  Patients soon become deconditioned and unable to functional.