Video script: how is pain produced?

This content is designed for the participants of the GGC Pain Management Programme.

There are lots of different systems within the body. Each has its own role in order for the body to function, and many different systems work together at the same time.

One of these systems is the nervous system and it has lots of important roles.

Today we’re going to be talking about how ALL pain, whether acute or chronic, is produced, and we can’t talk about that without learning more about the nervous system.

In the previous presentation we talked about the important protective function of pain.

It’s like an alarm going off to alert us to danger. In the pain service we often talk of our nervous system as a really sophisticated alarm system which is designed to detect and respond to threat.

Our nervous system is made up of different components.

There are millions of sensory receptors throughout the body. They communicate with the peripheral nerves. These in turn communicate with the spinal cord. The spinal cord is the link between the peripheral nervous system and the brain, both for transmitting information FROM the peripheral nervous system TO the brain, and TO the peripheral nervous system FROM the brain.

There is no beginning and no end to this process. It’s more like a constantly changing loop and exchange of information. But we have to start somewhere, so we’ll start by talking about the sensory receptors.

There are different types of sensory receptors throughout the body, and they are all stimulated by different things. Their job is to gather information on what’s going on both inside and outside the body to so the body can respond in the right way.

Mechanoreceptors are stimulated by mechanical forces like pinch or pressure.

Thermoreceptors are stimulated by changes in temperature

There are chemoreceptors which are stimulated by chemical changes both in an outside the body, so for example if you were stung by a bee or a nettle

When any of these receptors are stimulated at a level great enough, they will release their own chemicals which then stimulate the nerves that are sensitive to those particular chemicals. This is the same for all sensory receptors.

There is a particular type of sensory receptor, called a nociceptor, that can be stimulated by tissue damage. This could be in relation to an acute injury such as a sprained ankle, or something more longstanding such as Arthritis. But before we go on it is important to stress that pain is not in itself a sign of tissue damage, and the severity of pain we experience does not correlate to the amount of tissue damage present. This will be explained in the next presentation.

If nociceptors are stimulated then, like the other types of receptors, they will release chemicals which cause an electrical impulse within the peripheral nerve. This impulse is then transmitted along the length of the nerve to the spinal cord.

The spinal cord acts like a sorting office for all of this incoming information from the body. Some of this information will be sent up to the brain “special delivery” or first class if it might be something the brain needs to respond to urgently.

Some of the information that may need to be attended to, but not so urgently, will be sent up 2nd class.

And some information may be discarded by the spinal cord instead of being sent up to the brain, because if the brain had to attend to every piece of sensory information from the body all of the time it would be overwhelmed by information and couldn’t do it’s job properly. For example, you do not constantly need to be aware of the feel of your clothes on your skin!

So for example, if you were to place your hand on a very hot surface your thermoreceptors and nociceptors would be stimulated. The peripheral nerves would transmit these messages to the spinal cord. The spinal cord would then send this information up to the brain special delivery. The information needs to get there quickly so the brain can respond by sending a message down to contract the muscles to pull the hand away from danger.

So what does the brain do with all of this incoming information from the tissues?

Well, outwith our consciousness, outwith our control, the brain is trying to evaluate if the incoming information means there is a threat to the body.

But the information it receives are just electrical impulses from parts of the body. It’s not specific enough, on it’s own, to make an accurate judgement, and so the brain has to use other factors as well as the incoming information from the tissues, to make this call.

This is going to be discussed in more detail in an upcoming presentation, so all I’ll say on that for now is, remember that messages from the tissues alone are not enough to produce pain.

So if the brain concludes the messages it has received are not a sign of a threat to the body, it can release a bunch of chemicals that damp down future incoming messages of this kind. We often talk about these as “happy hormones” like endorphins.

These turn down the volume of the nervous system

But what if the brain concludes there may be a threat to the body? It releases a different kinds of chemicals. These are ones which turn up the volume. They ramp up the sensitivity of the nervous system.

So one of the brains important roles is to produce outputs which will protect the body. And pain is a very effective way of doing this.

End of video transcript

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