Your guide to understanding pain

Everyone has experienced pain. But how exactly does your body process this sensation?

How do you feel pain?
When you cut yourself, the pain stimulates specific pain receptors, and this stimulus is transferred via specialised nerves to the spinal cord and the brain. The pain stimulus is processed in the brain, which then sends an impulse down the spinal cord, via nerves which command the body to react. An example of this would be if you withdraw your hand from a very hot object.

Pain receptors are present everywhere in the body, especially the skin, surfaces of the joints, the lining around the bone, walls of the arteries, and certain structures in the skull. The brain itself does not have any pain receptors at all. Extreme pressure, heat or cold, or substances released upon trauma or inflammation, can all stimulate pain receptors.

What is "fast pain" and "slow pain"?
A pain stimulus - if you cut yourself - consists of two sensations. The first one is the so-called "fast pain" sensation, and is experienced as sharp. After a few seconds, this goes over into the sensation of "slow pain", which is more a dull and burning pain and can last for days, weeks, or even months.

Fast pain makes the body withdraw immediately from the pain stimulus, in order to avoid further damage. Even strong painkillers may not overcome this pain. This is why you need a local or general anaesthetic during surgery.

The response of the body to slow pain is to hold the affected body part immobile, so that healing can take place. The impulse from slow pain is distributed to many areas in the brain, leading to a whole range of symptoms such as suffering, difficulty in sleeping, because the pain stimulates the "wake centre" and a depressed mood.

When a surgeon cuts a bowel, this is not painful at all. But for the surgeon to get to the bowel, he has to cut through skin, and that is why you need anaesthetic. However, massive injury to an internal organ like the gall bladder, the uterus or heart can be severely painful. This pain often radiates or is referred to other parts of the body. Opioids prescribed by a doctor are very effective in treating this type of pain, while local anaesthetics also easily take this type of pain away.

What can the body do to temper the pain sensation?
Your body reacts to pain in three ways:

1. When you get hurt, you instinctively rub the painful area, which partly relieves the pain. Rubbing or pressing stimulates certain other nerve fibres, whose input in the spinal cord get preference to the input from the pain nerve fibres. So rubbing or pressing can actually block the pain sensation.
2. When a pain stimulus reaches the brain, the brain puts a brake on the pain impulse as it enters the spinal cord.
3. In the pain-processing parts of the brain there is a system of natural opioids (as endorphins), which are released when a pain impulse reaches the brain. They block transmission and perception of pain. Exercise increases the levels of endorphins.

Health24.com, updated January 2008