Nerves, danger messages and pain

Ion channels, receptors and action potentials

Last month we began to explore the role of nerves in the pain experience. We talked about 'nociception' – danger messages that a nerve or nerves will send to the brain. You may recall that these electrical impulses themselves are not a 'pain message' and that the pain experience is a brain based construct using all relevant information for that time, place and experience.

Let's look at nerves in more detail. Nerves from the tissues (muscles, skin etc) to the brain will only send quantitative data and not qualitative. The nerves do this via receptors or ion channels which are positioned at the end of the nerve and 'open and shut' in response to stimuli. They are made of proteins and respond to 3 differing stimuli:

• Temperature changes, such as hot and cold
• Mechanical changes or stresses, such as stretching and vibration
• Chemical changes in the tissues, such as inflammatory by-products, histamine, adrenalin, stress hormones like cortisol.

Opening ion channels allow for enough positive charges to flow into the nerve, thereby 'exciting it'. At a critical level of 'excitement', the nerve will 'fire off' an electrical impulse to the brain via the spinal cord. This is called an action potential. It is this message (and the intensity of it) that the brain uses to decide whether a pain experience will result from it. Can you see that the ion channels and therefore the messages to the brain will revolve around the stimuli of temperature, chemical or mechanical?

Another amazing fact about receptors is that they are in a constant state of change or remodelling (like the rest of our body eg skin cells). Receptors close, move and open every few days and will do so in response to these 3 stimuli. When a nerve is under greater levels of stimulation, more receptors will form and open. We can call this an 'over-excited' or 'over-sensitive' nerve. Here are some common examples we see all of the time:

• poor postures of the neck and upper back, increasing the pulling stresses in shoulder and upper back nerves
• anxiety and stress can increase the number of open chemical ion channels in all nerves
• inflammatory products such as histamine in a newly sprained ankle will increase the opening of the chemical ion channels.

An 'over-sensitive' nerve will send increased intensities of danger messages and your brain will need to sit up and take more notice of this. The brain is more than likely to say "hey, this is enough of a danger message to decide I am in pain."

And there is always a more hopeful and positive side to these facts! Receptors and ion channels can close by decreasing the levels of these 3 stimuli. And less ion channels opening will mean less danger messages to the brain. Sound great?

How do we do this? By reducing the chemical and mechanical loads on the nerves. There are many many ways, but here are a few:

• unload the nerve mechanically such as through movement, changes in posture, better muscle strength and endurance to get you through your days, better work place ergonomics
• improve the health of your nerve tissues such as through nerve gliding exercises to improve the blood flow to the nerves and their protective sheaths
• de-stressing and reducing anxieties, such as through education, psychology, relaxation techniques, drugs such as anti-depressants.

So as you continue to work on your good postures, build 'core' and trunk strength and slide your nerves in all those fancy ways, remember that you are not only having a positive impact on your muscles and joints, but also your nerves. You are helping to 'dampen them', making them less sensitive and reducing the levels of nociceptive danger messages to your brain.

Nerves as a part of the danger alarm system

Pain is a highly sophisticated alarm system that is designed to warn the body of danger. We all need it to keep ourselves and our tissues safe.

Nerves conducting messages from our muscles, skin and joints are only a part of the system. Today we will explore why there is no such thing as 'muscle or joint pain'.

Take the example of a paper cut on the end of your thumb. Sensors on the end of the nerves that supply the skin of that thumb will detect some damage to the skin. Alarm bells will 'ring' at these sensors and an electrical impulse travelling at 150km per hour will tell the brain "there's something going on at my thumb." The brain will take this message and will use that with other pieces of information to produce (or not) an experience of pain. Such other information could include the intensity of the alarm signal, visual inputs of the sight of the blood, visual impact of realising the deepness of the cut, memories of this happening before and really hurting etc.

This alarm system from the tissues (skin, muscle, joint) to the spinal cord and brain is called 'nociception', which means 'danger message'. From the example above, it can be seen that nociceptive messages along the nerves does not always result in pain. You may have experience this yourself when noticing much later that you have a little cut on your thumb with the presence of dried blood, but can't recall when you had cut yourself.

Nociception is only one small part of the pain experience.

We all have nociception going on all of the time- quite often beyond our consciousness. However most of us do not feel pain all the time. The brain has not thought there needed to be any concern to worry or alert you that you are or your tissues are actually in danger.

Even more interesting is that pain can be experienced without any nociception at all. Take emotional pain. Or strange tales of husbands experiencing 'labour like' pains when their wives are giving birth, or twins who feel the pain of the other.

So it can be said that pain does not 'live' in your muscles, skin or joints. It is nerve sensors that do - alerting the brain and consciousness that danger is about. Pain is the complex construction as your brain evaluates these danger messages with other information relevant.

You can impress your dinner party guests that what you hear about targeting 'muscle and joint pain on the Panadol and Voltaren ads on TV is not entirely true from a physiological view!

More on nerves, their sensors and nociception next time.

Tabitha shares her top tips on exercising at your desk without getting off your bum

Working in an office chair can cause all sorts of pains – or irritate existing ones. You may find that your lower back becomes stiffer, sorer and more tired as the day progresses, and opportunities to move about are hard to find. Instead of enduring the pain or abandoning your post, try these gentle, easy and fast exercises – each of them targets lower back pain, and all can be done without leaving your chair!

Active Sitting

Place your feet flat on the ground, hip width apart, with your knees and hips bent at 90 degrees (adjust your chair height if necessary).

Rock your pelvis forwards and backwards to find where your pelvis becomes level – check that you have a small curve in your lower back and that you're sitting up on your sit bones.

Grow tall from there, gently drawing the shoulders back and down a fraction and imagine you're holding a mango between your chin and your chest.

Hold that posture for 30 seconds, adding 30s each subsequent day to wake up your core postural muscles which support your spine. Try linking it to an activity you have to do regularly, like answering emails!

Seated slow march

Set yourself up in the active sitting posture (see above). Take a deep, wide breath in to prepare. As you breathe out, lift your pelvic floor, deepen your naval to your spine and maintain that posture as you slowly lift one leg up just enough to lift your knee from the seat. Do not rock your pelvis!

Hold there for a deep, wide breath in. As you breathe out, lift your pelvic floor, deepen your navel to your spine and lower your foot (in a controlled way) to the ground.

Do the same on the other side and repeat for a total of four on each leg. The exercise will challenge your core muscles so that they continue to support your back throughout the work day.

Hug knees

Push your chair away from your desk and lean right forward over your legs, hugging around your knees. Hold this stretch for 30 seconds and then come back up gradually. You should feel a gentle stretch in your lower back.

Reverse the car

Set yourself up in the active sitting posture (see above). Place your right hand on your left knee, and reach your left arm around to hold the back of the chair, turning through your spine as if you're reversing your car.

Stay there for 20 seconds, growing tall through the spine and breathing deep and wide. Repeat on the other side. You may feel this stretch in your back, chest or shoulders.

Buttock Stretch

Set yourself up in the active sitting posture (see above). Rest your right foot on top of your left knee. Push the right knee down gently with your right hand as you lean forward through your trunk. Hold for 30 seconds then repeat on the left. You should feel this stretch in your buttock muscles.

You can do these in any combination, and try out what works best for you. When you activate your core muscles like this then you will relieve pain both now and in the future!