Explaining Pain

Explaining how the nervous system contributes to chronic pain

By Coralie Wales, reviewed by the Chronic Pain Switzerland National Advisory Panel

If you live in chronic pain it is important to know that your nervous system changes in response to pain, and can become somewhat unpredictable when viewed traditionally. The process is called "Central nervous system sensitisation" and it causes the pain experience to become a highly distressing, misunderstood, little explained "snake eating its tail" situation where things can progressively deteriorate.

Did you know that your thoughts, feelings, and movements are all players in exciting or inhibiting this process? Central nervous system sensitisation is affected by all these things. There are chemicals that are associated with thoughts, feelings and emotions, and some of these calm down the system, some of them excite the system.

The pain experience is related to activity in ascending, central and descending processes of the central nervous system (spinal cord and brain).

  1. The pain experience is related to activity in ascending, central and descending processes of the central nervous system (spinal cord and brain).
    1. They transmit messages to the brain about damage or threat in the tissues
    2. Signals can also come to the brain about the health of the nerves themselves. This is called neuropathic or neurogenic pain
  2. Central processing

    In the spinal cord the central nervous system can become highly sensitive to stimuli from both within and outside the body. This process is referred to as Central Nervous System Sensitisation.

    In this situation, the ongoing pain has a lot to do with the process of nervous system adaptation. It is like the nervous system becoming a very sensitive and high quality amplifier.

  3. Descending Fibres from the brain to the body via the spinal cord
    1. This involves the sympathetic nervous system (fight or flight),
    2. Also involves the parasympathetic (rest and digest), endocrine (hormone production), immune (defence) and motor (movement) systems. All of these nerve fibres will make a contribution to the pain experience.

 

The Sympathetic and the Parasympathetic Nervous systems work to balance out each other so that we can function optimally in response to stimulation from our external environment.

The "Sympathetic" component allows us to respond to emergencies. It is the part of the nervous system responsible for protecting us by distributing the charged chemical called "Adrenaline". Adrenaline is one of the "stress hormones". This chemical gives us the "adrenaline rush" if we choose to jump out of an aeroplane with a parachute ("Skydiving") or we choose to bungie jump or go white water rafting. We have made a conscious decision to perform this type of activity and whilst it produces the adrenaline that is about emergencies, it is also fun, so we produce other chemicals including endorphins. We are pretty much in control.

Sometimes however we produce adrenaline because of an unexpectedly stressful situation - like a car accident or a family emergency - and adrenaline helps by supercharging us with oxygen which immediately activates the muscles, dilates the pupils and helps us to be physically "superhuman" in order to deal with the situation. On a very primitive or basic level in days gone by we may have had to fight for our survival or to escape the enemy. Hence the term "fight or flight". Think of how we might need this response in a threatening situation. It is either defend ourselves, or escape!! Fight! Or Flight!

So adrenaline is good in this situation. It helps us react.

If we are stressed over a long period, however, it becomes less appropriate to produce adrenaline. We then produce another chemical called "cortisol". Too much of this chemical can be damaging to our brains and other parts of the body. Chronic stress makes people sick.

So how do the descending fibres work in chronic pain?

The descending fibres transmit chemicals down to the spinal cord where there are chemicals coming up from the body. The mix in the middle is what is important. If there are more excitatory chemicals than inhibitory chemicals, we will have more pain. If there are more inhibitory chemicals than excitatory ones, then we have less pain. All of this is a procedure being regulated constantly in response to the brain's instructions. And the amazing thing is -

ALL OF THIS IS HAPPENING BELOW OUR CONSCIOUSNESS.

Normally, we have a fairly even mix between the ascending and descending chemicals. Things are on an even keel. For example, you knock your knee on the coffee table for the 50th time this year, and you notice the pain. But then you get busy, answer a phone call, get involved in a conversation, and you are not experiencing pain, and may not even remember it until you see the bruise that evening in the shower. You have experienced it so many times, the brain says, "don't worry, no big deal, I will send down some inhibitory chemicals to sort things out!"

There are significant links between the nervous system and the immune system which affect the experience of pain. Go to "my immune system and pain"