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Nerves are not like the cord on the toaster– Neuroscience Nugget No. 14

By Timothy Cocks Neuroscience Nuggets 04 Jun 2015

I’ve never been able to find a proper reference for it, but I’ve read somewhere that there is something like 72 kilometres of peripheral nerves in the adult human body. Whether this number is accurate or not, it’s safe to say that there is a lot, but with the increasing trendiness of the brain in pain research, this continuous, mechanical, dynamic, neuroimmune structure often gets forgotten.

There’s a pervasive conceptualisation out there in the general public (and large sections of the clinical community too) that equates nerves to power cords – ‘dumb’ wires that simply carry electrical signals to and from the brain. But the cord on your toaster is nothing like your peripheral nerves, which are alive, moving, always changing and constantly adapting.

If you cut the cord on the toaster, there won’t be any toast – nothing; you might as well put your vegemite and peanut butter back in the cupboard and throw the toaster away. But if you cut or damage a nerve, it will react with a complex cascade of neuroimmune responses – there will never be one molecular mechanism involved; it will be a combination of processes such local inflammation, neurogenic inflammation, immune responses, endoneurial fluid pressure changes and ion channel changes.

Additionally, there will be changes in the brain as the cut bit still tries to represent what it innervates and the brain tries to compensate and adapt. Some of these brain changes will remain long after the injury, with epigenetic changes in a number of brain areas evident 6 months after peripheral nerve injury (Tajerian et al 2013) and glial cells remaining ‘experienced’ and on alert for years (Banati et al 2001).

Nasty pain and stress states may ensue.

But there is so much rich, therapeutic narrative in the story of the peripheral nerves – take ion channels for example- there is around a million in a neurone, mostly at the terminal and nodes of Ranvier (that is how the action potential can jump over myelin). After an injury a nerve will make heaps more of these at the site of damage, all ready to act in response to mechanical, stress, immune or environmental stimuli. But these channels are turned over every few days and numbers can reflect the perceived need for protection of the human. This changeability should be a cause for hope that symptoms can and will change.

The broader stories of the peripheral nerves can help explain symptoms, inform clinical reasoning and engender wonder for the neuroimmune system as a therapeutic target.

Imagine a toaster that could repair its own cord, reorganise its heating elements and make the toast for you!


-David Butler and Tim Cocks



Banati RB, Cagnin A, Brooks DJ, Gunn RN, Myers R, Jones T, Birch R and Anand P et al (2001). Long-term trans-synaptic glial responses in the human thalamus after peripheral nerve injury. Neuroreport 12(16) 3439-3442.

Tajerian M, Alvarado S, Millecamps M, Vachon P, Crosby C, Bushnell MC, et al. (2013) Peripheral Nerve Injury Is Associated with Chronic, Reversible Changes in Global DNA Methylation in the Mouse Prefrontal Cortex. PLoS ONE 8(1).

(Full references available at links above)


  1. Thanks David for reminding us again about those “Issues in the tissues”. I’ve stolen your analogy for myself and already used it several times.

    With all due respect to you EG, I am very shocked by your statement in reply to the post “Closer to pain”

    ” How to relate this to the clinic? Forget about careful physical examinations for starters. Forget about detailed histories. Forget about choosing a particular physical technique to use. None of it matters. None of it makes the slightest bit of difference to the client. All one needs to know is: 1) are there any red flags? 2) where is the pain? and 3) How long has it been there? That’s it. Then work out some way in which you might be able alter the client’s perception. Lots of ways. Read through the old blog posts”

    The above statement is in such contrast to this post. I can assure you, as a sufferer that my issues in my tissues mean a great deal to me. Equally I am a human being, a patient and not a client……….

    Maybe I’ve read what you said but not understood what you meant. Different realities again……..

    DD London
    Enjoying my terrace 😎🍷🍴

  2. I missed reading this blog nugget til today.

    DB, it was designed to be a bit shocking…sometimes I wonder if anyone reads, the comments being so few and far between.

    It really is possible to treat most people very effectively without any of the usual steps we undertake. So I’d encourage others to just discard huge chunks of usual assessment phase and see what happens.

    There’s two advantages of this approach. 1) I get to find out what is essential and what is window dressing. So far I have found that most of it is window dressing and completely unnecessary. 2) it makes me rely more on careful observation, which is a much sharper tool than questioning.

    LBP: Where’s the pain? How long have you had it? What do you think caused it? Does it restrict you moving? Can you bend back and forward? Show me. Had this before? Ok, lie up on the bench and let’s have a look.

    I admit, that’s 6 questions, not 3(!), but it takes only 2 minutes. Nothing rushed, that’s just how long it takes.

    I say this with one important proviso: if things don’t look quite as they ought, I will always take the time and care needed to ensure I know what’s going on. That will involve asking a lot of extra questions and drilling down into the issue.
    An example of this would be severe pain or an absence of pain on palpation.

    Getting to know the person in more depth is something I do during the treatment (using conversational tone rather than interview style).


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