To understand the pain relief mechanism, we need to know how the pain is generated. Once, we get familiar with the path and the constituents involved, it becomes rather easy to get acquainted with this system and how it can be prevented.
PAIN MECHANISM
Pain is all about nerves that run through out our body. The mechanism is not very complex but the system of neurons (basic unit of nerves) and their transaction sometimes gets confusing. Anyhow, to get it simple, let's see what it's all about.
Planted throughout our body tissues are pain receptors. When we experience any injury that could be from burning, cutting, tearing, fracturing, freezing or crushing, these receptors are stimulated which in turn send pain signals to the brain through nerves via cervical spine and spinal chord. When it reaches to the brain, the signal is passed on to other nerve cells that carry it over to the Cerebrum and Limbic system of the brain.
THROUGH THE PATH
The path is very much obvious now, but throughout the path we have several structures which play their part to pass the information of injury to the central nervous system (the brain, spinal chord).
On the way right form the pain receptors, pain nerves carrying the information mix up with position sense nerves, temperature sense nerves, vibratory sense nerves and muscle control nerves to get larger when entering into the spinal chord.
Before entering into the spinal chord it naturally forms two roots. They are the frontal or back root (dorsal root). The Dorsal root is responsible for the pain signal to be carried through.
Right into the spinal chord, the dorsal root forms a relatively short nerve called the Interneuron. From here, right out of the spinal chord there is a nerve tract called Spinothalamic Tract which runs to the brain.
When in brain, the pain information is distributed to several regions, including the medulla, cerebellum, pons, limbic system and somatosensory cortex.
Simultaneously, as a natural counter mechanism, brain modulates the incoming pain signals by sending it down to the spinal chord to stop the pain signal being generated there. This special path is called the modifier pathway. Hence the pain is naturally nullified.
But what happens if this natural process doesn't work well. Definitely, a person experiences acute pain or chronic pain. It becomes even worse if the inflammatory pain is also triggered. The inflammatory response is a complicated local reaction, involving numerous body chemicals, blood vessels changes, temporary or permanent tissue damage. It can be either chronic or acute in the end because it inflames all the structures at the injury site.
PAIN RELIEF MECHANISM
There are different ways to get a relief from the pain. As we have just discussed that the pain's hub is in the spinal chord having NMDA receptors from where the pain is generated and passes on to the brain. So we need to stop the efferent nerves entering into the spinal chord before it could produce pain. The natural modifier pathway does the same. But sometimes it is beyond the scope of the natural mechanism to counter pain that usually forms a wind-up nerve to aggravate the pain in the due course.
In spine related pain the zygapophyseal joints are responsible for an acute pain. The nerves from these joints are again lead to the medal branches of the dorsal nerve root in the spinal chord. But here we could block the joints by a surgery to stop the pain element going through. A good block of these joints in turn, actually blocks the medial branches of the dorsal nerve root and pain is averted.
For an inflammatory pain which could be associated simple by an injury or other joint diseases or inflammation that affect the organs, a different mechanism may be involved. For the relief mechanism of a simple injury related inflammation, a localized medication which could heal up the wound is beneficial because it helps the accumulation of white blood cells to get normal and stop sending the pain signals to the spinal chord. For other joint related diseases that are associated with the pain even surgeries of those particular organs are done to relief the patients from the pain. It may include myocarditis, colitis, nephritis etc.
Different drugs are used to prevent pain and all of them have their own mode of action and mechanism. Among them, the commonly used drugs are NSAID's (non-steroid anti-inflammatory drugs). But other drugs like anti-depressants, anxiolytics, anticonvulants, cardioconvulsants, cardiovascular agents, local anesthetics and general anesthetics and opiods are also used to address the pain..
They act on different areas of the pain path.
Opiods and NSAID's act on C- fibre pain receptors.
Membrane stabilizers (anticonvulsants, topicals, transdermal) act on AB-fibre touch receptors where usually the inflammatory pain is triggered.
NMDA receptors or opoids act on the NMDA receptors in the spinal chord.
Tricyclics (alpha-1 and alpha-2 blockers) act on the descending pathway (pain modifier)
and Antidepressants, anxiolytics, anticonvulsants, sleeping agents act centrally in the brain. These drugs play a defining role in reducing the pain.
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