What is pain?

Pain is a feeling in your body that you do not like. You feel pain if you cut or burn yourself. You have pain if you break a bone, pull a muscle or get cancer.

How can pain be useful?

Pain tells you there is something wrong with part of your body. If you feel pain, you protect yourself better from harm. If you did not feel pain, you could die from appendicitis! You would not know you had anything wrong with you. Another example is found in people with leprosy (fortunately, a very rare condition in most countries), who cannot feel pain, so they damage their fingers and toes and need to get them amputated.

Children learn very quickly that they should not touch hot things!

How do you feel pain?

Usually, you feel pain when a part of your body has an injury or disease affecting it. The damaged part of the body produces chemicals that irritate the nerve endings (which act like sensors) and trigger messages to be sent through your nerves to the brain by way of the spinal cord. The nerves work like wires carrying phone calls to a telephone exchange (the spine).

The spinal cord is the main nerve trunk that carries all of the messages from the body to the brain. It is, itself, really a complicated computer, a part of the brain. The spinal cord acts like a telephone exchange that receives phone calls and automatically switches them to the correct part of the brain.

The spinal cord runs through a tube that runs up the back of the spine. Strong bones (vertebrae) and gristle protect the spinal cord from damage.

Until recent years, doctors thought nerves carried pain messages directly from the diseased part of the body to the brain. This is partly right, but the story is more complicated than this.

The spinal cord receives electrical messages from the nerves, analyses all the messages and sends another signal up to the brain. When everything is working properly, it relays accurate messages to the brain. The messages it sends are things like "my skin is warm at the tip of my finger" or "there is something pressing on the back of my hand".

The brain is the part of the body that lets you know what is happening to you. Different parts of the brain get signals from the parts of the body they are responsible for. Inside the spinal cord and the brain, the pain messages continue to be analysed until we notice that something hurts.

As well as this system, there are other nerves called "autonomic" nerves that normally control all the things we do without thinking about them, like sweating and shivering. These nerves, which can bypass the spinal cord, also carry pain messages to the brain. So, even someone who is paraplegic, with his or her spinal cord completely cut, can feel pain through these nerves.

How do you stop pain?

The best thing is to treat the cause of the pain. Medical science has developed ways to fix most pains.

• If you have appendicitis, you need to have your appendix removed.
• If you have a boil, you should get the pus out of it.
• If you have a broken arm, you should get it set in plaster to stop the bone ends moving over each other.
• If you have cancer, you should get some treatment for it.
• If arthritis is causing severe pain, a surgeon can operate on the joint and put in a new one.
• If you are having a baby, an anaesthetist can stop most of the pain by injecting painkillers around the nerves in the spine.
• If you have angina, a surgeon can graft blood vessels to get more blood to the heart muscle.

Pain relief medications help pain feel less severe until the body has been able to repair itself.

Why are some pains hard to treat with painkillers?

Some pains linger on, and there is no easy treatment for them. Examples of lingering pain are low back pain, cancer pain, the pain you get after shingles and the pains that people with diabetes get in their feet.

Some people get what are known as "phantom pains" after they have had a limb amputated - eg, they feel pain in a leg that is no longer there. Other people get severe pain that remains long after the initial damage seems to have healed.

These types of pain can be very hard to treat.

For more on chronic (long term) pain, see our topic Chronic pain

This article was written by Dr Leo Revell, a Waikato GP and member of the board of trustees of the Migraine Sufferers' Support Group. This article was originally published in the Waikato Times newspaper. Reviewed by everybody, December 2003.