Sometimes, simple little bits of information can lead to minor revelations. I had one such moment during the recent Explain Pain, 3 day event in Melbourne. Professor Bob Coghill was discussing the transduction and transmission of innocuous warmth:
Bob: “Innocuous warmth is transduced by specialised ion channels in free nerve endings of unmyelinated, small diameter and slowly conducting C afferents.”
Thinking me: Ok so far, but I need to dust some cobwebs off this information – it’s been a while…
“Warmth afferents increase discharge frequencies as skin temperature is raised within the innocuous range of 35 to 45 degrees celsius.”
Still with you Bob, and I’m thinking that the increase in firing rate helps to give us the ability to tell the difference between 35’C and 45’C – we are clever aren’t we. But why is the upper limit of innocuous warmth 45’C – what’s so special about this temperature?
“So, what happens at 45 degrees celsius?”
Oh wow, he just read my mind…
“Anybody use a crockpot, a slow cooker?”
“I’ve been using a crockpot to make yoghurt recently, so I’m sensitive to this setting”
“At temperatures of about 45 degrees proteins begin to denature – basically stuff gets cooked”
Huh *exclamation of minor revelation*
“So at 45 degrees, you tend to move from the innocuous realm to the noxious realm and things can start to hurt. I’m in the process of moving house at the moment and I don’t have my thermometer in the place I’m living in, but I still want to make yoghurt. I need to know if I have heated the milk enough so that the yoghurt will grow when I incubate it over night, but not so much that I won’t kill it when I dump the culture in. So what do I do? I stick my finger in and if it hurts I know I need to wait a little longer. When I stick my finger in the milk and it doesn’t hurt, I know that it’s not noxious and I know that when I dump all the little bugs in, the lactobacilli and whatnot, they are not going to get denatured and die, instead they will be all happy and turn it into nice tasty yoghurt.”
Of course, this makes so much sense – we’ve evolved a system that will warn us when we are at danger of being cooked – brilliant!
So here is a great little nugget that might be useful when Explaining Pain (or making yoghurt). A very practical example of the ‘built-in’ alarm system with a lovely example of how ‘clever’ (and specific) this system is – tuned as it is to protect us from potentially damaging, and protein denaturing, temperatures.
PS: What might happen to proteins at around 15 degrees celsius, the point at which cold becomes noxious?
Mobilisation of the Neuroimmune System is coming! Based on the latest evidence, the Mobilisation of the Nervous System course has been updated and re-written ‘from the basic science up’, integrating the neuroimmune system as a critical player in learning, memory, movement and sensitivity. The MONIS course provides a clinical reasoning framework to identify those patients who will benefit from neurodynamic mobilisation and the essential practical skills to examine and manage the physical health of the nervous system. Adelaide 24-25 July and Sydney 1-2 August 2015