"Hi, me again, C fibre.
"Yesterday, I told you a bit about myself..
"Today I thought I might add a little bit more. Every day, it seems, more is known about the kinds of things that can, potentially, bother me.. people seem to find this stuff fascinating, and, I suppose, so do I - ultimately, I am the one affected by it all..
"Anyway, first, I want to show you a cartoon drawing somebody did - remember I was telling you I had a long arm and a short one?
|C-fibres enter spinal cord, their information ascends via the spinothalamic tract. Many kinds of C fibres convey many kinds of sensory input, including "pleasant", not just for temperature or nociceptive information|
"Nice picture of my short arm, don't you think?
"Here's another cartoon - I'm in yellow, hanging out with a sympathetic fibre and some other body bits. As you can see in the picture I've become "sensitized" - when I get sensitized I seem to bother the heck out of macropages, then they squirt stuff back at me that makes me even more cranky. And so it goes. Before you know it I have adrenaline receptors growing all over my membrane. Honestly some days it feels like a total school yard in there, complete with all the usual assortment of bullies and bullying going on.
|Sensitized peptidergic afferent neuron|
"Things can get quite nasty, with a lot of inflammatory comments being passed back and forth chemically, plenty of swelling, redness, heat, primary hyperalgesia and my personal favorite, "Functio laesa" going on.. isn't that a fun term? All it means is loss of function, but life is so bland, usually, that I like when I get to speak Latin.
"Now, things usually die down in a few days. I mean, none of us really can keep that up for very long. At least, most of the time we don't even want to. Not that there aren't diseases that occur sometimes, where the positive feedback loop just gets bigger and bigger.. unless there is a good drug to stop it, like Rheumatoid Arthritis for example.. But usually things just go back to ho-hum normal. The swelling drains away and everybody stops being bothered by each other.
"If this happens inside a nerve trunk though.. ooh.. that's an enclosed space. It's a lot harder for inflammation to settle down because the situation is complicated by lack of space and no lymphatics that anyone knows about, so, potentially threatening pressure and not the greatest drainage.
"A nerve trunk is like a busy freeway with traffic zooming through tubes in both directions in many lanes, separated by curtains only. My job is the same as ever: provide excretion - I mean, secretion - fertilizer, kind of.. "trophic factors" is the polite term - to tissue, and accept trophic factor from the tissue in return. I deliver it back up to my cell body, or head, in the dorsal root ganglion, and there, I can make stuff I need to keep myself in good shape. This is all transported back and forth on transport tracks that have nothing to do with the information flow I am also able to provide, when required. All neurons do this, by the way.
"Here's a picture somebody drew ages ago, showing how I look all in black, inside a nerve trunk.
|Wonderful old-timey picture of the innervation of a nerve trunk and its vasculature|
"You can see there isn't much room in there. When axoplasmic transport is interfered with neurons can actually die! You can see why it's an important job - protecting the tissue inside a nerve trunk. If the nerves were to fail... well, just let's leave it at this: the nervous system as a whole is very protective of itself. I have that small role to play, but really, it never changes. What the nervous system might make out of my reportage, is something else entirely."
Nociceptive musings 3
Nociceptive musings 4
Nociceptive musings 6