G V Joshi
Taking ‘painkillers’ or ‘analgesics’ as they are also called is the easiest way to get rid of headache or body ache or simply pain. But how do painkillers works? How do they know where the pain is?
The unpleasant sensation of ‘pain’ is the main symptom in almost all medical conditions. Studies show that ‘pain’ is the most common reason for visiting your family doctor’s clinic or visiting a hospital.
What is pain? The English word ‘pain’ probably comes from Old French (peine), Latin (poena – meaning punishment pain), or Ancient Greek (poine – a word more related to penalty), or a combination of all three.
In medicine pain relates to a sensation that hurts. If you feel pain it hurts, you feel discomfort, distress and perhaps agony, depending on its severity. Pain can be steady and constant, in which case it may be an ache. It might be a throbbing pain – a pulsating pain. The pain could have a pinching sensation, or a stabbing one. Only the person who is experiencing the pain can describe it properly. Pain is a very individual experience.
Types of pain:
(1) Acute pain: This can be intense and shortlived, in which case we call it acute pain. Acute pain may be an indication of an injury. When the injury heals the pain usually goes away.
(2) Chronic pain: This sensation lasts much longer than acute pain. Chronic pain can be mild or intense.
Pain is often caused by intense or damaging stimuli such as stubbing a toe, burning or cutting a finger, putting iodine on a cut and the like.
It motivates withdrawal from damaging or potentially damaging situations, protection of a damaged body part while it heals, and avoidance of similar experiences in the future.
Most pain resolves promptly once the painful stimulus is removed and the body has healed, but sometimes pain persists despite removal of the stimulus and apparent healing of the body; and sometimes pain arises in the absence of any detectable stimulus, damage or disease.
Aristote did not include a sense of pain when he enumerated the five senses; he, like Plato before him, saw pain and pleasure not as sensations but as emotions.
According to Descartes, particles of heart activated a spot of skin attached by a fine thread to a valve in the brain, where it opened the valve, allowing the animal spirits to flow from a cavity into the muscles causing them to flinch from the stimulus, trun the head and eyes toward the affected body part, and move the hand and turn the body protectively.
A number of theories of pain have been proposed beginning from the eighteenth century onwards. All these including the latest ‘gate control theory’ are far too complicated to understand for a common man, but a simple picture is given below.
The gate control theory of pain was put forward by Ronald Melzack and Patrick Wall in 1965. They proposed that there was a ‘gate’ mechanism in the central nervous system that opened to allow pain messages through to the brain and closed to prevent them getting through.
When we feel pain, such as when we touch a hot stove, sensory receptors in our skin send a message via nerve fibres to the spinal cord and brainstem and then onto the brain where the sensation of pain is registered, the information is processed and the pain is perceived.
According to the gate theory, as these pain message come into the spinal cord and the central nervous sytem (before they even get to the brain), they can be amplified, turned down or even blocked out.
There are many accounts of how people injured on the battlefield or in sports games don’t feel any pian from their injuries until afterwards. This has something to do with the brain being busy doing other things and shutting the gate until it can pay attention to the messages.
The medicines that help to achieve absence of sensation of pain without losing consciousness are called analgesics to painkillers, but the exact reaction that takes place in the body after ingestion of a painkiller and how it helps relieve the pain is still not clearly understood by physicians.
Scientists know that different painkillers act in different ways and help lower pain and inflammation. Studies show that painkillers act on the central nervous systems and help achieve topical or systemic analgesia. They usually start to work when they reach the bloodstream through the stomach (within 30 to 60 minutes).
Aspirin sold under brand name Aspro is one of the most common painkillers used by everyone sometime or the other. How does Aspirin relieve pain and inflammation? A simple picture is as follows.
Damaged and pain-causing cells produce large quantities of an enzyme called cylooxygenase-2. This enzyme in turn produces a chemical called prostaglandin, which sends a message to the brain signaling that a specific part of the body is in pain. The chemical also causes the injured area to release fluids, causing it to swell or become inflamed.
Aspirin adheres to the cylooxygenase-2 and prevents it from producing prostaglandin. As a result, some of the pain signals do not reach the brain and less pain is felt. Also, the inflammation is minimized due to the lack of prostaglandin production.
Acetaminophen sold under different trade names like Tylenol or parcetamol is a non-prescription pain reliever and fever reducer. It is also one of the most commonly used non-aspirin painkiller. Compared to other pain relievers, Tylenol is less likely to cause ulcers and to interact with other medicines.
However, it may be more likely to cause liver damage, especially when taken at very high doses or in people who already have liver damage.
Opium based analgesics like morphine, act on various parts of the central nervous system by binding to natural opium receptors. They are used for higher levels of pain relief. However, they can be easily overdosed and become addictive.
There are some people who do not feel any pain when injured. They are suffering from a rare genetic disease called Congenital Analgesia.
One might think that this is a good thing, but it’s actually a life-threatening condition. Pain serves as a warning against injury, so people who don’t feel it can be severely injured or hurt by things that most of us would react quickly to.
How fast does pain travel? Our nervous system has over 10 billion nerves cells in a network that covers every square inch of our skin and organs. Like insulated electric wires the cells in the central nervous system have a similar protection to prevent the leakage of an impulse from its proper path-way.
If you should hit your finger with a hammer, the sensation of pain will reach the brain before you can blink an eyelash. The speed of an impulse, including that of pain, varies considerably in humans. But it has been found to be able to travel as fast as 107 metres per second, almost one -eighth the speed of a bullet.
(PTI Feature)
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