Friday, February 15, 2013

Peripheral nerves and gorillas 2

Peripheral nerves and gorillas 1.

Today I spotted what I think might be a gorilla. Inattentional blindness. So I edited my first wikipedia page. More about that later.

Over at SomaSimple Barrett started yet another thread on his favorite topic, ideomotor movement: Revealing the Shadow II.  You can read it there if you wish. He asked what the difference was between his baby, simple contact, and my baby, dermoneuromodulation.

There is so much we agree on, except for one thing - he doesn't see the outer layer of the body as being very consequential [which may be because he is so tired (as am I) of all the operator nonsense that has grown up over the years that has to do with this layer].

What layer am I talking about? The epidermis/dermis/hypodermis layer. The blubber layer.

The nonsense we agree on has to do with people imagining that they are stretching the fascia inside it, instead of realizing they are setting into motion all sorts of motor output by the nervous system, a clear sign of the nervous system responding to outside exteroceptive input.

We both agree on that, and it's a huge overlap, almost entire. However, his stance is that ALL movement in response to treatment is outward from the brain, is ideomotor, from the brain, linked to some kind of idea or thought, conscious or unconscious.

This I cannot agree with. I think at first there is reflexive movement. A whole lot of reflexive movement. No thinking required. 

Can hypodermis "move"?
The blubber layer in question has no motor volition within itself*, other than autonomic. That is its only motor business. [And, just for the record, as a therapist I'm only interested in neural structure within that layer, and the vessels that feed it. There is only so much life left, and I'm spending mine studying that which has agency in the daily normal pain free life of the entire human organism. I could not care less about adipocytes etc..]

To me, this means that any "movement" that's palpable, by me as therapist, especially the small stuff, is likely to be of the fluid kind; one can sense pulsing or whooshing just below the skin, sometimes. I am pretty sure by now this is reflexive response, only.

A quick and dirty look at the peripheral nervous system
Mesodermalists ALWAYS think about muscle first. They can't help themselves. It's how they learned the body. When they learn nervous system, they ALWAYS learn the motor output system. That is to say, the corticospinal paths and the corticobulbar paths, the paths the brain uses to send commands to muscle. Striated muscle. The red stuff in pictures of the body. The meat. They are muscleheads. They want to relate everything, everything to movement, to motor control. When they treat, they imagine they are stretching muscle. They want to stretch it, knead it, strengthen it, lengthen it, soften it, harden it, get rid of what they think are its trigger points, whatever. They imagine if they can corral this misbehaving mesoderm somehow, all will be well.

When musclehead mesodermalists think of the PNS, they think only of motor nerves that go to muscle. But seriously folks, motor neurons are CNS, not true PNS, and muscles are just meat puppets at their ends.

I look at the peripheral nervous system differently, because although it has the same mommy, ectoderm, it has a different daddy - instead of being made out of neural tube, it's made out of neural crest.

Motor neurons that have their cell bodies inside the spinal cord, have neural tube daddies, go out to muscle targets, and have hitched a ride with their siblings, the rest of the peripheral nerves, which contain a variety of other kinds of neurons, all of which have neural crest as their daddy.

They might all travel together, but they have very different roles, and destinations. Some are bringing in information to tell the brain, and some are taking information from the brain or at least from the CNS, out to the muscles. Muscles are puppets of the nervous system. They do not have any volition of their own. Not that the spinal cord can't affect them if it wants to. I do not dispute that.

The autonomic system takes care of daily business "locally" which is to say, more peripherally, outside the spinal cord, with cell bodies in ganglia that live near to, but not within, the spinal cord. Not that they don't communicate with the spinal cord. They do. The peripheral nervous system, made from neural crest, and its sibling, the central nervous system, made from neural tube, talk to each other all the time and like conjoined twins born of the mother, ectoderm, share a lot of information of the signaling sort about the body they share.

But they can also operate - a little bit - autonomously from each other. What I'm saying is that although the central nervous system has evolved capacities that are light years more sophisticated than anything the PNS can do by ITself, like think, the PNS was running organisms all by itself very well before vertebrates came along about 500 million years ago, whose fish ancestors organized a CNS into a little something called a "spinal cord" with a little "brain" on one end. I call that, collectively, the critter brain. It's been busy running physicalities of various shapes and sizes and species way longer than the more sophisticated bits of CNS have, which, in humans, are only a couple hundred thousand years old. It developed "automaticity", auto-nimity, autono-mousness, autonomy, in that length of time. Little by little, as the brain (in the beginning just the critter brain only) grew bigger through evolutionary time, it developed more capacity to inhibit the peripheral nervous system. The critter brain and the PNS have had a lot longer together to figure each other out and learn how to work together. The human CNS, nice and fluffy though it is, is really new, only a couple hundred thousand years old; the old CNS has no problem at all knocking it offline in order to deal with itself, particularly if it senses any threat to itself coming in from the PNS.

Some of the different neurons in the PNS include sympathetic, parasympathetic (but not out to skin in humans, except lips, as I recall), and weird things called visceral afferents that do not belong to the first two categories, which are afferent, but do have efferent function anyway, sort of. The other big class of neurons are exteroceptive sensory neurons, which include big fast fibres that are well-connected to the primary sensory cortex of the brain, and lots of interoceptive neurons which also report to the brain but more slowly and through slower pathways.  They have cell bodies in prevertebral ganglia, sympathetic chain ganglia, and dorsal root ganglia. Each ganglia is like a little brain. It can make certain programed decisions by itself. As long as everything is going along in a fairly ordinary way.

A quick and dirty look at visceral afferents
See "visceral afferent neurons" (VANs), notes from Chapter 2 in Jänig's huge book, Integrative Action of the Autonomic Nervous System: Neurobiology of Homeostasis. VANs come in two main flavours, spinal visceral (SVANs) and vagal visceral (VVANs).

Here is a slide that lays out the intricacies of what visceral afferents do.

If you happened to miss it, here it is again, spelled out:
1. They report to CNS
2. They modify regulation of viscera by extracentral reflexes in prevertebral ganglia (NOTE: extracentral - outside the CNS. They have some autonomy. And some agency. But I doubt they can "think".)
3. They "release neuropeptides from peripheral endings, e.g., CGRP and Substance P - these travel both ways in neuron" (so presumably they could secrete them at both ends?)
4. Through their trophic capacity they might "influence synaptic connectivity in spinal cord with second-order neurons." (We know how well this goes, when it comes to situations like central sensitization - the brain doesn't like this a whole lot usually..)

They are not "efferent" in that they can't "move" anything - their business is reported to the older parts of CNS like crazy though. Which is why they are deemed to be "afferent" - they hang out with the sympathetic efferent fibres but are neither sympathetic nor parasympathetic - they are their own kind of unclassifiable neuron. See Is there anything “autonomous” in the nervous system?

The only thing they can do is squirt stuff out onto their target organ, which, of interest to us, in the outer layer, is the wall of blood vessel. Why? Because hypodermis contains so freaking much vasculature! Why? Because it's a cooling organ for all the heat we make as a) mammals, and b) mammals with freakishly huge brains that are only 2% of our body but use 20% of all the fuel! We run hot! No wonder we lost our fur.. 
Our hypodermis/dermis contains 10 times more blood than it needs for its own maintenance. Our nervous system keeps itself cool by running huge amounts of blood out toward the environment to cool it off. Sweating helps. It's hugely important, and requires a huge amount of finely controlled vasculature. Controlled by the PNS, monitored and regulated by the CNS, as long as things are going along normally.. 

Think of the effort involved in driving a car. Not much, right? Just enough steering to keep the car on the road between the ditches. 

Some visceral afferents are mechanoreceptive with high threshold, and others are mechanoinsensitive/chemoreceptive. 

If we skip through to notes on section 2.4.2, we meet up with the spinal kind, out in skin. 

The rest is a very detailed examination of all the reflexive connections between visceral afferent ascending pathways, and descending critter brain pathways which can be up to 5 times more powerful. [Anyway, the chapter is intense, but I made VERY careful notes, so if you're interested, go to the link and download the pdf directly.] 

My contention is that until and unless the critter brain gets this force of nature, this visceral afferent "behaviour", subdued, the human part of the brain won't be able to access the motor output part of itself very readily. 

Inner jellyfish?
It's all well and good, but no movement of this kind (to my knowledge) involves any "thought" - it seems all still pretty reflexive at this stage. Might as well be jellyfish neurology, this part is so old. Jelly fish are not noted for having much in the way of intellect. They can move in the wild, but if we were to consider visceral afferents as a trapped inner jellyfish, they can't go anywhere anymore - all they can do is squirt potentially irritating, annoying juice on their surroundings. 

Maybe it all works like a mirroring of evolutionary history of nervous system formation: visceral afferents are the inner jellyfish to the critter brain (fish onward) which came along and learned how to deal with the inner jelly fish just fine, long before humans came along with our big fat socially responsive neocortices.  Manual therapy soothes the critter brain AND human brain in a manner just sufficient and necessary to help the three nervous system aspects sort themselves out, and especially to help the critter brain to subdue the nasty sensations the jellyfish have created, and then the human brain makes friends once again with the critter brain. Ah sweet relief. THEN movement can happen unimpeded, and will feel good. Nociception will have changed to yes-ciception. The critter brain will relax/stretch its limbs, the human brain will stand up, bend its spine, twist its torso freely all around. 

When I went to look up hypodermis in Wikipedia, I realized they listed all the contents of hypodermis with out mentioning cutaneous nerve. So I made an edit to include a short point on them, with a link to Wikipedia's own page on cutaneous nerves. 

Seriously, how could I let that stand uncorrected? 

Cutaneous nerves
If I have anything that remotely resembles an obsession, this is it. And I really despair that no one but me, apparently sees the importance of these, how superficial they lie, especially their rami, all the way out to skin [scroll down for pictures], and how easy they are to construct new treatment models around. See Nash et al 2004 for a description of the skin ligaments that form neural tunnels for rami to branch out to innervate the outermost layer of skin.  

The cutaneous nerves are the nervous system's, the nervous systems', own feelers, out into the passive, heavy, thick skin organ all round the outside of the body, which is laced with all those spinal visceral afferents which can leak all those annoying substances on them not only from vessels on the outside of them but also on the inside of them, and woe betide any cutaneous nerve or ramus thereof which happens to be a bit entrapped somehow, because its neurons' membrane permeability will be adversely affected by compression or tension, and some of that nasty business will get straight on them and may well bug the heck out of them. Once that happens it's like being in a bank as it is being robbed. Bam! lockdown. No one can leave until after the police have arrived and have interviewed everyone in turn. In the body, movement can't happen until the neurology straightens itself back out again [or a bigger threat looms..]. I don't really care what kind of movement it is or it isn't - I think motor output phenomena happen very close together, but sequentially. This is the way I like to splice together the story of what happens to the nervous system as it resets its function to being "normal" again, able to move. I don't think movement requires much "thought", conscious or unconscious. I think once it turns back on, it's turned back on, period. Just like the doors are unlocked at the bank, once everyone has been interviewed by the police and the teller hits the switch. Then everyone is free to move again. Home. 

To sum up:
We humans love our illusion that we are in the driver's seat, that we "own" our bodies, that our nervous systems are under our control. 
Heck no. 
Our nervous system is the boss of us, not the other way round. It keeps us alive [whatever "us" is..]. It puts us to sleep at night so it can fix itself, restore dopamine stores, glutamate, whatever, keep us breathing, our hearts pumping, make us roll over without waking us all the way up. In the morning, our nervous system wakes "us" up, because its bladder needs to be emptied, and it's hungry and wants "us" to go get it something to eat. Nervous systems were around long before one end got very fluffy and decided to call itself "human." Once our nervous system shuts off, so do we. That's it. 

It can be a bit disconcerting, I realize, to face the fact that the "we" we think we are, is mostly just a projection out to the world, produced and directed by a nervous system that has been continuously evolving throughout evolutionary time, isn't finished, that needed a social module. But that still has bits of itself that are still a lot like the first bits to ever have evolved. 
"We" float from day to day embedded in a living ecosystem we recognize as "our" physicality, a bunch of cells made from atoms that came from stardust that stay organized as a "body" because a tiny percent of all the cells making it up are really long, skinny and can talk really-really fast to each other. And burn up a huge amount of oxygen and glucose in the process. 

Imagine three concentric spheres, one inside the other like Russian nesting dolls: 
1. Innermost sphere = peripheral nervous system (minus motor neurons) and visceral afferent system, or jelly fish brain. It can sting! And it does, all the time. As long as blood flow is sufficient, its annoying secretions do their immediately local task and are quickly washed away before they bother any other neurons. No prob. PNS looks after itself, plus a whole lot of circulatory issues, reflexively. Axon reflex, etc. It talks to itself through its ganglia. The central nervous system listens in, offers its opinion, keeps the car (the body) on the road (of homeostasis).   
2. Next sphere out = critter brain. This is the spinal cord and brainstem, and hypothalamus, a few bits of ancient cortex - insular cortex, anterior cingulate, limbic; also motor output but not very sophisticated, mostly there to approach mates or prey or escape being somebody else's lunch  ... Invented by fish ancestors, we have all of this in common with every other vertebrate species on the planet. Its job is to monitor and regulate, guard the boundaries of organismic existence. Social grooming evolved at this stage though, so there was some social connecting, within and between species. Food was usually involved, at first..  
3. Third and outermost sphere = human brain. Voluntary control of striated muscle. Shares motor control with critter brain. Can interrupt critter brain control for short periods of time, like not blinking, like not breathing. But can't keep it up for long. Has sensory afferent "spies" all the way out to skin. Needs to know what's out there in the environment, so if it sits on a thorn, for example, it can know to move. And when, depending on context. Needs to make contact with other creatures to feel safe, succored, socially accepted, mandatory while still an infant, finds pleasant even as adult. Loves to pretend, then believe, that it has dominion over self and even over others and over imaginary domains it has invented, like social structures. Even over other peoples' body structures. See operator models.

All three share the same peripheral nerve trunks.  

If the sk-input isn't right, the output will falter. People come to manual therapists because they want their skin organ, loaded with those visceral afferents, held in various directions, or moved certain ways so their nervous system can get a fix on the problem and solve it, so they can move freely once again. The only system that can "move" anything in the skin layer is the sympathetic NS (smooth muscle, vascular constriction, sweating) and visceral afferents through vasodilation. Those are cellular "movements" - but they can add up, I suppose... reflexively. The human brain can drag its hurting physicality off to a therapist and together they can work out what the system might need to get it rebooted so that it will hurt less. We hope. 

When we put our hands on somebody's skin surface we are NOT touching muscle directly. Muscle does NOT respond immediately, usually, unless someone flinches away because of expectation, because you haven't created a safe context, because you are creating some nociceptive input for them to deal with. But if all is set up to transpire smoothly, the autonomics start up right away, and the critter brain comes over to check you out. There isn't any thought to any of this - it's all hard-wired and normal. After the first two systems have checked you out, done their job, are satisfied, the critter brain can relax, because it managed to finally squirt the right stuff from the drug cabinet in the brain stem down the spinal cord: then - and only then, in my opinion [and I'll go to my grave being pretty sure about this], the critter brain will let the human brain move the body again - no problem. 

I do not think it's appropriate to skip over any of this information, or assert that one or more of these steps don't matter, or leave them entirely out of an explanatory model, or mistake an explanatory model for a treatment model. 
I would assert that understanding how the system works, how its parts work and what they need, is important, so that you can move ever further away from the possibility of creating any chronic pain patients. The world does not need more of these, especially when there are scads of human primate social groomers around, and all they need in order to work more intelligently, is to take on more and better information. 
We can do better. So much better. 


*There isn't any somatic motor output of the striate muscle persuasion anywhere in the hypodermis layer except for in the face and front of neck, as far as I have learned, to date. Please tell me if I'm mistaken on that. Striated muscle is found throughout the hypodermis layer there. Why? Because the face and front of neck are built from neural crest, and neural crest is very, VERY weird. It can build ANYthing. But it's still ectoderm, not mesoderm.  

Adv Physiol Educvol. 30 no. 1 9-12


Barrett Dorko said...

Diane, You've taken what to many is surreal and made it accessible. I think now that the movement I sense on the surface is reflexive and often turns into movement secondary to thought. When that happens is hard to say. Self-correction is present across this spectrum.

Diane Jacobs said...

Thank you for your comment Barrett. I'm glad I was able to make this very complex business more clear.