Pain usually arises from special nerve endings called nociceptors. These detect damage to the area in which they are situated and send a message to the brain saying something is wrong. The damage might come from piercing the skin with a sharp object. Or it might arise from inflamed tissue such as an infection or an arthritic joint. Sometimes the pain will come directly from a damaged nerve itself as in trigeminal neuralgia or sciatica.
Whatever the cause of the pain, the pain signal takes much the same route. It travels along the nerve to the spinal cord where it is then relayed up to the brain. It is only when the pain signal reaches the brain that we are conscious of the sensation of pain. This physiological fact is important for some methods of pain control where the pain signal is prevented from reaching the brain.
Pain Reflex Arc
An important aspect of pain physiology is the pain reflex. We’ve all experienced this. You touch something very hot or sharp and immediately your arm is pulled away. It feels a though you have felt the pain and pulled your arm away. In fact your arm is pulled away milliseconds before you experience the pain.
When the pain signal from this type of injury reaches the spinal cord it triggers an immediate response to the arm muscles to pull away from the offending object. This occurs just before sending a signal to the brain to tell you that something painful has happened. It saves milliseconds of time and this helps prevent further damage. The reflex does not require any conscious thought from you: it would still happen if your head was missing – for a short while at least.
Major Pain Causing Syndromes
These syndromes are classified according to the supposed origin of the pain.
- Neurological pain: causes range from neuralgia due to viral infection of the nerve as in herpes, nerve entrapment such as sciatica or due to no known cause as in trigeminal neuralgia. Pain is usually experienced as lancing or burning along the track of the nerve.
- Muscle and ligament pain: the kind of thing that arises from overuse injury, back strains, cramps and the like.
- Non-neurological pain: all pain is neurological in that the pain travels through and is felt in the nervous system. This group covers various pain causing problems that don’t quite fit into the other groups. It can include such diverse causes as cancer, lack of blood flow (in the heart for example) and joint disease.
- Central pain: although the brain itself does not have any pain receptors, damage to certain areas, from stroke for example, can give rise to pain. This may in some instances be due to non-pain signals from the body being interpreted as pain by the disordered brain.
- Psychological pain: this can be a tricky one when discussing with patients the cause of their pain. They may well think that you are telling them that they are imagining the pain. They are not of course, the pain is real, it’s just there is no physical component that is found as a cause. Patients with depression are said to be frequent sufferers of this type of pain. You could however look at it the other way round: anyone suffering from pain to which no one can find the cause is likely to get depressed pretty quickly.
This article is for information only. If you have any health concerns you should consult your doctor.
Resource
Neurology: A Concise Clinical Text. Swash and Schwartz. Pub. Bailleire Tindall 1989
