Nociceptive musings 5
Nociceptive musings 6
The family tree
"Hi there, me again - C fibre. I wondered if you might be interested in my family tree - I don't have photo albums but I think you should know my background, at least a little bit, so you'll know better where I'm coming from.
"I was reading my last post, and noticed something in the Levi-Montalcini article that I thought I'd pick up on, and explain."
"The peripheral nervous system of vertebrate animals includes three kinds of nerve cells: sensory neurons, which transmit impulses from sensory receptor structures to the brain; motor neurons, which innervate the striated, or skeletal, muscles, and autonomic neurons, which regulate the functional activity of the circulatory system, the organs, the glands and the smooth muscles (such as those of the intestine)."
"So, OK, I realized I needed to clarify something; here it is... (deep breath): I disagree with lumping "motor neurons" in with peripheral nervous system as though we were all the same. I mean, yeah, we are all long neurons, and we travel together long distances woven throughout the Body in the same nerve trunks. But the whole categorization of neurons simply by location is completely misleading, and I wish it would end. It makes me feel quite nociceptive - a mild case of peptidergia comes over me whenever I see it in print anywhere.
"Here's the thing (another deep breath...) : we come from the same "Mom," ectoderm, but we have different dads.
"Sort of. Let me explain.
"It has to do with stages of division. See the pretty coloured picture to the right? OK, so it's all "ectoderm," or Mom stuff. However, the colours represent the "Dad" in the situation, OK?
"The Dad of motor neurons is the purple stuff. All neurons from "PurpleDad," aka NeuralTube, make up brain and spinal cord. They are usually short, and there are billions and billions of them... Lower motor neurons are still from PurpleDad - their heads live up in the spinal cord - and they have only one arm.. yeah, it's a very long arm - like, it can reach all the way to the big toe, all that.. but still, it's a Purple kid.
"PurpleDad's kids are usually way more enclosed, inside the CNS, which makes lower motor neurons kind of an exception, but ... there is no getting around the fact that apart from that long arm sticking out, they are CNS neurons.
"There is a huge variety of Purple kids, and they make important stuff in there. But you know, they're a lot like city kids; they're used to living enclosed, separate-from-the-rest-of-the-body kinds of lives. They are mostly self-referential. It takes an awful lot to get them to pay attention to the Body, usually. Like, they'll pay attention to it fast if there is something wrong with it - but I, together with a whole bunch of other nociceptors, or a huge number of pleasant-signaling C fibres, have to make a huge noise to get their attention - usually they are completely oblivious. Unless they practice some sort of deliberate body focused exercise regularly, or meditate.
"Anyway, the big take-home point I want to make here is that just because neurons end up physically in some place outside where they came from, doesn't mean that they completely change their attitudes or habits or language or who is most important to them. And lower motor neurons whose job is to make striate muscle jump are central nervous system neurons, not peripheral neurons. They're there to drive tractor, but that doesn't mean they understand the soil or how it smells or how to grow anything in it. They don't really have their heads in the game, do they?
"My dad is GreenDad - his formal name is NeuralCrest. His offspring kind of scattered everywhere. We are sensitive to signaling, and we lovelovelove to signal, and we can speak more signaling languages than offspring from PurpleDad (at least I think we can..). I like to think we ended up a lot more autonomous, self-sufficient, innovative as a result. We'll talk to anybody!
"My head lives outside the spinal cord, outside the central nervous system, in a ganglion. I have scads of siblings. The entire autonomic nervous system is sibling. All the Schwann cells are siblings. All the glia in the brain are siblings - they have the same GreenDad. [Well, except for microglia. They're kind of more like birds, like little modern dinosaurs, they're from so far back in embryonic time.] There are GreenDad neurons in the central nervous system too - but they are inside cranial nerves. Not all the cranial nerves, but most.
"And do you know what else? My green siblings that live in the brain help to manage all the purple siblings. Oh yes they do.
"You know what? Teeth! Teeth are my GreenDad siblings! True fact. Look up "neural crest" and you'll find out the amazing variety of offspring my dad made in the beginning of the Body that our mom pretty much built, that we all help comprise, and now look after. Well, all the GreenDad kids do, at least..
"Here is something cool - pretty much the whole face of the Body we look after came from GreenDad, even all the bones and muscle and skin and cartilage and glands and stuff! Oh yeah.. and throat. Things needed for swallowing. GreenDad kids. Siblings. They can't signal the way neurons can, electrically, but they can talk chemically, for sure, and they talk a lot that way, to us, their GreenDad neuron siblings...
"So, whenever I read something about the Body, or Nervous System, or signaling, or how smart glia are or how glia manage neurons in the brain, I already know who is who, and it makes sense. GreenDad is usually responsible. [He got around some back in the day, he did.. ]
"So, what about the BlueDad, you might be wondering... ? BlueDad's kids are skin cells, keratinocytes. They aren't neurons, but they do express TRPV channels, and are heavily involved in all the usual neuroendocrine signaling that goes on in skin. [GreenDad (my dad) has some skin cell kids too. Of course. Ha. He left kids everywhere.]
"I'll talk more about my GreenDad again some time, maybe, because of all the Dads, I think he has the most interesting kids, and not just because he's my particular dad - this is an objective opinion - I mean, c'mon.. teeth?? :D I am not kidding. The Body wouldn't even have a face if GreenDad hadn't been there to help build one."
1. Xiaoning Han, Michael Chen, Fushun Wang, Martha Windrem, Su Wang, Steven Shanz, Qiwu Xu, Nancy Ann Oberheim, Lane Bekar, Sarah Betstadt, Alcino J. Silva, Takahiro Takano, Steven A. Goldman, Maiken Nedergaard; Forebrain Engraftment by Human Glial Progenitor Cells Enhances Synaptic Plasticity and Learning in Adult Mice. Cell Stem Cell, Volume 12, Issue 3, 342-353, 7 March 2013
2. Rita Levi-Montalcini and Pietro Calissano; The Nerve-Growth Factor: A New Tool for Manipulating Neurons. Scientific American, June 1979
3. Nicholas Boulais, Laurent Misery; The epidermis: a sensory tissue. European Journal of Dermatology. Volume 18, Number 2, 119-27, march-april 2008, Review article
4. Biology 4361; Neural Crest Cells. July 24, 2008