Introduction
Gaining an understanding of pain helps reduce the fear and anxiety surrounding it and this can help reduce the impact pain has on someone (Moseley and Hodges 2001).
Pain is defined as ‘an unpleasant sensory and emotional experience with actual or potential tissue damage’ (Merskey 96).
This definition considers the multi- dimensional nature of pain. It appreciates that pain is an actual sensory experience but that it also has an emotional component and that pain can be caused by potential as well as actual damage to tissues.
People traditionally think that pain is due to injury or damage and that it is a warning to be very cautious so as to avoid further injury and therefore further pain. But in reality, due to changes within the nervous system, the feeling of pain can far outlast the actual tissue injury and persist even after the injury has healed.
There are three dimensions of pain. The sensory (the actual feeling of pain, its nature and locality), the cognitive (what we think about the pain and how interpret its meaning and context) and the affective (how we behave in reaction to it).
People’s thoughts and emotions (cognitions) can directly affect the healing of an injured tissue (Cole-King and Harding 2001). This can be due to people’s behavioural changes or even just by the way they view their problem.
It’s probably easiest to understand the physiology of pain by looking at the various stages of the process and how they can be affected.
The injured tissue, the nerve endings and the peripheral nerve.
When a body tissue is injured various chemicals are released into the area around them. These chemicals irritate, or sensitise, the pain nerve endings sending a message towards the spinal cord and then onto the brain. This nerve now becomes more sensitive and is more able to be irritated again. Once irritated, this nerve can also send pain messages spontaneously, without any more irritation.
As the tissue heals less chemicals are released, the nerves are irritated less and gradually they become less sensitive. As the nerve returns to normal it sends less pain messages to the spinal cord and onto the brain so less pain is felt.
Sometimes this sensitivity can last a while after the tissue has healed, causing ongoing pain. If the tissue doesn’t heal and remains weak then the irritation of the pain nerves can continue.
When nerves in an injured area become irritated they can then in turn irritate neighbouring nerves in healthy tissue. This means that pain can be felt in an uninjured area and feels as though the pain is spreading. This reverses when healing occurs and the sensitivity reduces.
It is therefore important to behave in a way that best allows tissue healing so not to maintain the sensitivity of either the tissue or the nerves.
Pain Behaviour
You can generally refer to pain behaviour as adaptive or maladaptive.
Adaptive behaviour is appropriate for the situation, e.g. avoiding painful movements for a day or two after hurting your back or limping after spraining an ankle. This prevents further injury and allows the early stages of healing to take place. As the pain reduces and movement becomes easier, you gradually return to normal movements and normal activities. This allows the healing tissue to be exposed to normal stresses and strains, which helps it get stronger.
Mal- adaptive behaviour could either be not resting enough in the early stages or by resting too much and avoiding movement for too long. Often people get the balance wrong and can delay the healing process.
The Spinal Cord
When the first nerve reaches the spinal cord it releases chemicals which stimulate a second nerve and the pain message is then send up the spinal cord to the brain.
Again, the more pain messages that this nerve receives the more sensitive it becomes, the more likely it is to be further stimulated and more likely to send more pain messages to the brain. It too can become so sensitive that it can send messages to the brain without being stimulated by the first nerve. So now, ongoing pain can be felt even if the tissue that was initially injured has fully healed.
The junction between the first and second nerves (synapse) is influenced by various chemicals which can either increase or reduce the ability of the pain message to be passed between them. If the message is prevented from passing on to the second nerve it isn’t stimulated and the pain message is prevented from passing to the brain.
The Brain Stem
The brain stem is an area just before the brain itself which controls a lot of automatic body functions such as breathing and heart function and it also transmits up and down going messages to and from the brain, including pain messages.
There are certain parts of the brain stem that control the body’s natural pain control system. When activated they produce chemicals (opiates) which can inhibit the pain messages.
The effect of thoughts and emotions
Different chemicals and hormones are released by the brain in different mind states and these are different if you are happy or sad, confident or fearful, relaxed or stressed etc.
Research in recent years has shown that they can influence the effect of these chemicals passing between the first nerve and the second. They can either block them or increase their effect. They can also increase the sensitivity of the second nerve and help release chemicals from the second nerve back to the first nerve which stimulates the first nerve to release more chemicals. So the whole process becomes self- perpetuating.
Different moods and emotions can also affect the brain stem as it has direct links with the part of the brain which is responsible for thoughts, emotions and interpretation. Again, negative mind states can inhibit natural pain control and positive mind states can improve it.
Someone who is positive and confident is less likely to increase the sensitivity of their nervous system and this can help control the pain. They are also more likely to adopt adaptive behaviour and this will help them recover from the injury more quickly.
It is well documented that psychological and behavioural factors are better predictors of recovery than physical factors (Jensen et al 1991, Krisson and Keefe 1998).
It has also been shown that the body releases steroids, which impair healing, and inhibits the production of hormones essential to the healing process in response to stress (Padgett and Glaser 2003, Lundberg 2005, Rabin 2005). So emotional state can directly affect the body’s ability to heal.
The Brain
Once the pain message reaches the brain it is passed through several different areas. The sensory areas determine the area and type of pain while other areas conceptualise and rationalise its meaning and develop a plan of action as to what should be done about it.
The sensory experience of pain can be influenced by the thoughtful (cognitive) functions of the brain. So pain might be felt much more, or the nature may be more unpleasant, in the presence of negative feelings such as stress, fear, anger or anxiety.
Via the previously explained connections, other factors in people’s lives such as relationships, social and occupational can affect their painful condition, not just the actual injury.
Certain areas are related to memory and the physiological processes behind memory and pain are intimately connected. It is possible for the sensation of pain to be maintained purely from the brains memory of it, without any further pain messages from the tissues. Pain memories are maintained much more strongly in situations of negative emotion or trauma and so the situation in which the pain started can help maintain it.
For example, if someone was injured through an abuse or assault, and they had emotional problems as a result, the brain is more likely to remember the pain from the injury even when the injury has healed.
As less extreme example would be someone who hurts their back lifting. Whenever they are confronted with lifting in future they are anxious an afraid and the situation itself and memory of the past situation may play a role in future episodes of pain (Chapman 1996).
The sensory areas of the brain have a kind of body map with each area of the body imprinted in it. Over time if this area is continually stimulated, if the sensitive nerves or the area responsible for pain memory keep sending messages to it, it can adapt to this input and become used to it. So pain can become part of the sensation for that part of the body. This area can also spread out into other areas in the body map and the feeling of pain can then be felt in other previously uninjured areas of the body (Flor 1997).
Summary
The processes involved in the actual feeling of pain involve the tissues at the site of the initial injury, the nerves that transmit the pain messages and various parts of the brain involved in receiving and conceptualising the messages.
The processes are directed and controlled by chemicals which dictate the extent to which the messages can pass and these processes are influenced by both physical and emotional factors.
The way someone feels and behaves in response to injury are the most important factors in controlling the pain and promoting tissue healing and other aspects of their life can influence this.
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