SomaSimple Discussion Lists  

Go Back   SomaSimple Discussion Lists > WWW The Wild Wise World > The Rubbish Cube > Decontamination Room
Albums Quiz PubMed Gray's Anatomy Tags Online Journals Statistics

Notices

Decontamination Room A special place for toxic subjects. Handle with care.

Post New Thread  Reply
 
Thread Tools Display Modes
Old 04-04-2008, 07:57 AM   #51
gilbert
Senior Member
 
Join Date: Mar 2008
Posts: 305
Thanks: 107
Thanked 71 Times in 31 Posts
Default

Point taken.

I quite agree about the primacy of the nervous system, and about the importance of our practice being firmly grounded in reality. Just some of the tone of the posts occasionally gets me concerned. I don't think that replacing an extreme "mesodigm" with an extreme "neurodigm" is necessarily the best way forward for our profession. After all, without the mesodermally derived musculature the NS would not be able to do much

That said I know how DIFFICULT it is to change the way people think and work. (First you need to get people to think, which in itself seems nearly impossible at times.)

-Gilbert
gilbert is offline   Reply With Quote
Old 04-04-2008, 08:31 AM   #52
bernard
Admin, Moderator...
 
bernard's Avatar
 
Join Date: Mar 2004
Location: France
Age: 57
Posts: 12,227
Thanks: 589
Thanked 337 Times in 163 Posts
Default

Quote:
Originally Posted by gilbert thomson
After all, without the mesodermally derived musculature the NS would not be able to do much
After all, without the ectodermally derived nervous system the muscle would not be able to do... Nothing.
__________________
Simplicity is the ultimate sophistication. L VINCI
We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. I NEWTON

Everything should be made as simple as possible, but not a bit simpler.
If you can't explain it simply, you don't understand it well enough. Albert Einstein
bernard

bernard is offline   Reply With Quote
Old 04-04-2008, 09:58 AM   #53
nari
NeuroNut Evangelist
 
nari's Avatar
 
Join Date: Mar 2004
Location: ACT Aust
Posts: 8,241
Thanks: 1,427
Thanked 466 Times in 331 Posts
Default

I agree that the body's systems are interdependent to a certain degree.
You can take out various bits and pieces and the body will function normally (whatever the definition of narmality is).

The point quite a few members on this board are making is that the nervous system is often forgotten when dealing with pain/dysfunction that appears to be mesodermal in origin.
For instance, a painful neck that is pathologically OK, might be helped by mesodermal interventions. Or might not. Calming down a hypersensitive nerve or two can result in rapid resolution of pain and return of function. No guarantees either way, but no method or technique has those attached. Attention to neural sensitivity can be more effective and longer-lasting; and a few on this site are doing studies to indicate its usefulness.

Quote:
First, you need people to think, which in itself seems nearly impossible at times
Absolutely!

Nari
nari is offline   Reply With Quote
Old 04-04-2008, 06:26 PM   #54
Diane
Human Primate Social Groomer and Neuroelastician
 
Diane's Avatar
 
Join Date: Mar 2004
Location: Weyburn Sask.
Posts: 21,860
Thanks: 2,651
Thanked 5,449 Times in 2,475 Posts
Default

Ditto what Nari said, and Bernard.

I'd like to add that by turning out batch after batch of human primate social groomers focused only on mesodermally derived tissue, and what mobilipulating it ostensibly does to it biomechanically, and not providing us with the most coherent model or even the simplest model of how or why the organism responds and at what levels for better or worse, insults our (collective) intelligence, plus leaves us (collectively) vulnerable to wild goose chases like this whole microtubule fascination, and trying to latch on to them, link them into mesodermal derivatives without any real idea of what is actually talked about in the field.

Not that I'd know anything about that either...just that the topic of "microtubules"
  • seems like one of those "unnecessary hypotheses" that Occam "admonished" people to "eliminate"
  • seems to be considered quite a conceptual stretch at any level of examination, including at the neuroscientific level.
__________________
Diane
www.dermoneuromodulation.com
SensibleSolutionsPhysiotherapy
HumanAntiGravitySuit blog
Neurotonics PT Teamblog
Canadian Physiotherapy Pain Science Division (Archived newsletters, paincasts)
Canadian Physiotherapy Association Pain Science Division Facebook page
@PainPhysiosCan
WCPT PhysiotherapyPainNetwork on Facebook
@WCPTPTPN
Neuroscience and Pain Science for Manual PTs Facebook page

@dfjpt
SomaSimple on Facebook
@somasimple

"Rene Descartes was very very smart, but as it turned out, he was wrong." ~Lorimer Moseley

“Comment is free, but the facts are sacred.” ~Charles Prestwich Scott, nephew of founder and editor (1872-1929) of The Guardian , in a 1921 Centenary editorial

“If you make people think they're thinking, they'll love you, but if you really make them think, they'll hate you." ~Don Marquis

"In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists" ~Roland Barth

"Doubt is not a pleasant mental state, but certainty is a ridiculous one."~Voltaire
Diane is offline   Reply With Quote
Old 04-04-2008, 06:38 PM   #55
Diane
Human Primate Social Groomer and Neuroelastician
 
Diane's Avatar
 
Join Date: Mar 2004
Location: Weyburn Sask.
Posts: 21,860
Thanks: 2,651
Thanked 5,449 Times in 2,475 Posts
Default

Here is what Jeffrey Gray, author of Consciousness: creeping up on the hard problem, has to say, after writing from page 241 to p. 259 a careful description of the Penrose Hammeroff theory in quite a favorable light, actually:

Quote:
Conclusions
Despite its magisterial complexity, then, we see that, in the end, the Hameroff-Penrose theory of how different quantum superpositions inmicrotubules in different brain areas give rise to different qualia must rely for the origin of these differences on arguments taken from neuroanatomy and neurophysiology. And, despite its intricate Gothic architecture, the theory is incomplete. It offers no account of how differences at the Plank scale might relate to differences between qualia; nor of how differences in space/time in one brain might relate to differences in another brain observing the same scene at the same time. Nonetheless, the theory does offer an account in principle of the origin of differences in qualia. Whether even this is testable in practice is another matter...
(Apparently he died shortly after or before this book was published.)

Nowhere in the entire chapter is fascia mentioned. Why? because after embryonic differentiation occurs, fascia ceases to have any ability to signal anything but mechanoreceptors, physically, I should think.

Plus, there is the opinion of particle physicist Victor Stenger to consider. He says,
Quote:
In a 1999 paper, physicist max Tegmark looked at the problem of quantum coherence in the brain and determined that the decoherence timescales would be ten or more orders of magnitude shorter than the timescales for events in the brain. The brain is simply too large and too hot to be a quantum device, coherent or not.
__________________
Diane
www.dermoneuromodulation.com
SensibleSolutionsPhysiotherapy
HumanAntiGravitySuit blog
Neurotonics PT Teamblog
Canadian Physiotherapy Pain Science Division (Archived newsletters, paincasts)
Canadian Physiotherapy Association Pain Science Division Facebook page
@PainPhysiosCan
WCPT PhysiotherapyPainNetwork on Facebook
@WCPTPTPN
Neuroscience and Pain Science for Manual PTs Facebook page

@dfjpt
SomaSimple on Facebook
@somasimple

"Rene Descartes was very very smart, but as it turned out, he was wrong." ~Lorimer Moseley

“Comment is free, but the facts are sacred.” ~Charles Prestwich Scott, nephew of founder and editor (1872-1929) of The Guardian , in a 1921 Centenary editorial

“If you make people think they're thinking, they'll love you, but if you really make them think, they'll hate you." ~Don Marquis

"In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists" ~Roland Barth

"Doubt is not a pleasant mental state, but certainty is a ridiculous one."~Voltaire

Last edited by Diane; 04-04-2008 at 10:51 PM.
Diane is offline   Reply With Quote
The Following User Says Thank You to Diane For This Useful Post:
Ravensara Travillian (09-10-2012)
Old 05-04-2008, 04:01 AM   #56
gilbert
Senior Member
 
Join Date: Mar 2008
Posts: 305
Thanks: 107
Thanked 71 Times in 31 Posts
Default

Diane
You'd be encouraged by the amount of attention here in Australia directed towards the nervous system, neural mechanosensitivity, and pain science among normal Ortho PTs. At the Aussie Physio Association Musculoskeletal Conference in Cairns last October some of the topics were:
"training the brain" and "the brain in chronic pain" by Lorimer Moseley,
David Butler's "explain pain" workshop, some great research on central sensitivity following Whiplash by Michelle Sterling and others at the University of Queensland, low back pain and motor control changes in the lumbar spine (Paul Hodges)
There seems to be a widespread awareness of, and attention to, neural involvement in painful conditions which I think you would appreciate.
- Gilbert
gilbert is offline   Reply With Quote
Old 05-04-2008, 04:23 AM   #57
nari
NeuroNut Evangelist
 
nari's Avatar
 
Join Date: Mar 2004
Location: ACT Aust
Posts: 8,241
Thanks: 1,427
Thanked 466 Times in 331 Posts
Default

Gilbert, I'm gald to hear that.

I've been out of the workforce for 2.5 years and when I left the general orthopaedic focus was still very musculoskeletal, with passing reference to the nervous system.
However the 4th year students took a keen interest in neural matters in considering topics such as gait anomalies, the dreaded SIJ and pelvic issues.

I suspect South Australia would be something of a leader in managing pain - the home of Butler et al...

Nari
nari is offline   Reply With Quote
Old 05-04-2008, 08:06 PM   #58
marcel
SomaSimpler
 
marcel's Avatar
 
Join Date: Feb 2006
Location: The Netherlands, Amsterdam
Posts: 358
Thanks: 53
Thanked 116 Times in 39 Posts
Default

Regarding the "fuzz" of this thread; microtubuli do things to people


(Also) Looking at cellular level as a PT can be (is) a good thing for understanding and perhaps coming up with new ideas.
Of course one has to be cautious with publications; as shown all to clear in this thread.
Microtubili play a role in axonal transport (as far as I know; and have other functions) so why not look at that cellular part (D.Butler
paid attention in his book : the sens.nerv.sys.) but the info will only be important as it has it place in the bigger picture.

As a fresh PT (years ago) I was excited about hearing about nerve growth factors and thought about the possibillities for SCI-patients.
Still has to happen, unfortunately.

Just a question regarding this thread in general : is your contact with patients any similar how you replied in this thread?

Thanks,
Marcel
marcel is offline   Reply With Quote
Old 05-04-2008, 08:14 PM   #59
marcel
SomaSimpler
 
marcel's Avatar
 
Join Date: Feb 2006
Location: The Netherlands, Amsterdam
Posts: 358
Thanks: 53
Thanked 116 Times in 39 Posts
Default

Regarding the "fuzz" of this thread; microtubuli do things to people

Looking at cellular level as a PT can be a good thing for understanding and perhaps coming up with new ideas.
Of course one has to be cautious with publications; as shown all to clear in this thread.
Microtubili play a role in axonal transport (as far as I know; and have other functions) so why not look at that cellular part
(D.Butler paid attention in his book : the sens.nerv.sys.) but the info will only be important as it has it place in the bigger picture.

As a fresh PT (years ago) I was excited about hearing about nerve growth factors and thought about the possibillities for SCI-patients.
Still has to happen, unfortunately.

Just a question regarding this thread in general : is your contact with patients any similar to how you replied in this thread?

Thanks,
Marcel

adjusted....
marcel is offline   Reply With Quote
Old 05-04-2008, 11:11 PM   #60
EricM
Arbiter
 
Join Date: Mar 2005
Location: Nanaimo, BC
Age: 40
Posts: 1,809
Thanks: 1
Thanked 5 Times in 5 Posts
Default

Quote:
is your contact with patients any similar to how you replied in this thread?
Marcel, who is this question directed to?
__________________
Eric Matheson, PT
EricM is offline   Reply With Quote
Old 07-04-2008, 04:13 PM   #61
Diane
Human Primate Social Groomer and Neuroelastician
 
Diane's Avatar
 
Join Date: Mar 2004
Location: Weyburn Sask.
Posts: 21,860
Thanks: 2,651
Thanked 5,449 Times in 2,475 Posts
Default

Mo at Neurophilosophy blog turned up with a post today to do with this topic. By reading this post it's more clear to me what "microtubules" actually are, in the first place. From reading this, it seems to me that their "significance" if there is some, has more to do with brain/neuronal function/attempts to create stronger synaptic connection (neuroplasticity) and nothing to do with fascia. Nada.

The function of fascia appears to still be to physically hold things together, keep things from coming apart, no more; no matter how hard the fascialists try to bestow special microtubular powers of communication on fascia, if it had any, the neuroscientists would have probably noticed it by now.

This isn't to say that the mechanoreceptors strewn through the body, including through fascia, aren't important signalers. But they are ectoderm, not mesoderm.
__________________
Diane
www.dermoneuromodulation.com
SensibleSolutionsPhysiotherapy
HumanAntiGravitySuit blog
Neurotonics PT Teamblog
Canadian Physiotherapy Pain Science Division (Archived newsletters, paincasts)
Canadian Physiotherapy Association Pain Science Division Facebook page
@PainPhysiosCan
WCPT PhysiotherapyPainNetwork on Facebook
@WCPTPTPN
Neuroscience and Pain Science for Manual PTs Facebook page

@dfjpt
SomaSimple on Facebook
@somasimple

"Rene Descartes was very very smart, but as it turned out, he was wrong." ~Lorimer Moseley

“Comment is free, but the facts are sacred.” ~Charles Prestwich Scott, nephew of founder and editor (1872-1929) of The Guardian , in a 1921 Centenary editorial

“If you make people think they're thinking, they'll love you, but if you really make them think, they'll hate you." ~Don Marquis

"In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists" ~Roland Barth

"Doubt is not a pleasant mental state, but certainty is a ridiculous one."~Voltaire
Diane is offline   Reply With Quote
Old 10-04-2008, 07:41 AM   #62
bernard
Admin, Moderator...
 
bernard's Avatar
 
Join Date: Mar 2004
Location: France
Age: 57
Posts: 12,227
Thanks: 589
Thanked 337 Times in 163 Posts
Default

Here is the result of an experience on a two dimensional network:

If fascia is an elastic network then what happens when it is stretched?

=> Quite nothing since the property of an elastic network is dampening!
Of course, with a tri dimensional network the effect will be much more reduced.
Attached Images
File Type: jpg network_01.jpg (193.7 KB, 6 views)
File Type: jpg network_02.jpg (189.8 KB, 6 views)
__________________
Simplicity is the ultimate sophistication. L VINCI
We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. I NEWTON

Everything should be made as simple as possible, but not a bit simpler.
If you can't explain it simply, you don't understand it well enough. Albert Einstein
bernard

bernard is offline   Reply With Quote
Old 10-04-2008, 08:43 AM   #63
gilbert
Senior Member
 
Join Date: Mar 2008
Posts: 305
Thanks: 107
Thanked 71 Times in 31 Posts
Default

Very nice demonstration Bernard!

The physical effects of deforming the tissues are dampened, so any distant effects would need another explanation, (like a nervous system response).
gilbert is offline   Reply With Quote
Old 10-04-2008, 09:43 AM   #64
bernard
Admin, Moderator...
 
bernard's Avatar
 
Join Date: Mar 2004
Location: France
Age: 57
Posts: 12,227
Thanks: 589
Thanked 337 Times in 163 Posts
Default

Yes. A huge (100% in my picture) mechanical deformation ends, at a cellular level, in few micrometers.
This is why a mechanical aspect of energy is easily discarded.
__________________
Simplicity is the ultimate sophistication. L VINCI
We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. I NEWTON

Everything should be made as simple as possible, but not a bit simpler.
If you can't explain it simply, you don't understand it well enough. Albert Einstein
bernard

bernard is offline   Reply With Quote
Old 20-04-2008, 06:44 PM   #65
bobmfrptx
Senior Member
 
Join Date: Nov 2006
Location: central PA
Age: 54
Posts: 274
Thanks: 0
Thanked 2 Times in 2 Posts
Default

http://www.springerlink.com:80/conte...3270672354763/

More food for thought.
And again mechanotransduction is affected by tensions of stretch.
http://www.nae.edu/NAE/bridgecom.nsf...ks/MKEZ-65RHQL

Bob
bobmfrptx is offline   Reply With Quote
Old 20-04-2008, 09:17 PM   #66
marcel
SomaSimpler
 
marcel's Avatar
 
Join Date: Feb 2006
Location: The Netherlands, Amsterdam
Posts: 358
Thanks: 53
Thanked 116 Times in 39 Posts
Default

Hi,

I agree with Barett and Nari.

Funny that this afternoon I've read some of Barett's essay's, somewhere comes the point of " a patient believe's his/her pain is in the muscle, and it must be there because thats what he/she is being thought/told;.....(PT) education still focusses much on pain origin from muscle tendon etc.,... why? because the teachers where being told it came from there(connect.tiss.); in fact a belief that is quite strong even if being presented with modern ideas in contrary to it.
But what about the microtubules?
A year ago I saw something on tv about (near death,) out of body experiences. An idea was postulated that in microtubules the organisation of atoms & molecules was the perfect enviroment for quantum effects to have place.
I looked up the refferences and it turned out a dutch dentist had made up a quassi review of very common ideas on quantum theory, neurology etc.
I'd like to say : just leave the microtubules, the fibroblasts and the other cytes,blasts, clasts for doing what they do best.
__________________
Marcel
"It's a poor sort of memory that only works backwards".
Lewis Caroll
marcel is offline   Reply With Quote
Old 22-04-2008, 07:37 AM   #67
bernard
Admin, Moderator...
 
bernard's Avatar
 
Join Date: Mar 2004
Location: France
Age: 57
Posts: 12,227
Thanks: 589
Thanked 337 Times in 163 Posts
Default

Quote:
Originally Posted by bobmfrptx View Post
And again mechanotransduction is affected by tensions of stretch.
And again mechanotransduction deserves directly the nervous system.
__________________
Simplicity is the ultimate sophistication. L VINCI
We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances. I NEWTON

Everything should be made as simple as possible, but not a bit simpler.
If you can't explain it simply, you don't understand it well enough. Albert Einstein
bernard

bernard is offline   Reply With Quote
Old 26-04-2008, 07:11 PM   #68
Diane
Human Primate Social Groomer and Neuroelastician
 
Diane's Avatar
 
Join Date: Mar 2004
Location: Weyburn Sask.
Posts: 21,860
Thanks: 2,651
Thanked 5,449 Times in 2,475 Posts
Default

I finally got around to reading up on microtubules. I took a few notes from Gray's. Here they are. I've highlighted the word "microtubules" as it appears. It looks like they are involved mostly in axonal transport. Let's be clear - we're talking about microtubules in neurons here.

It seems their main significance is most cell types is in helping with cell division, and in neurons they get retained for transport duties inside the cells. It doesn't say anywhere I could find that they are involved in signalling between cells, even nerve cells, per se.

NEURONAL SOMA (CNS)

Membrane:

* plasma membrane of the soma is unmyelinated, and contacted by inhibitory and excitatory axosomatic synapses
* very occasionally, somasomatic and dendrosomatic contacts may be made
* the non-synaptic surface is covered by either astrocytic or satellite oligodendrocyte processes


Cytoplasm:

* cytoplasm of a typical soma is rich in rough and smooth endoplasmic reticulum and free polyribosomes
* this reveals a high level of protein synthetic activity
* free polyribosomes often congregate in large groups associated with the rough endoplasmic reticulum
* these aggregates of RNA-rich structures are visible by light microscopy as basophilic Nissl (chromatin) bodies or granules and are more obvious in large, highly active cells, such as spinal motor neurones, which contain large stacks of rough endoplasmic reticulum and polyribosome aggregates
* maintenance and turnover of cytoplasmic and membranous components are necessary in all cells
* the huge total volume of cytoplasm within the soma and processes of many neurones requires a considerable commitment of protein synthetic machinery
* neurones synthesize other proteins (enzyme systems, etc.) which are involved in the production of neurotransmitters and in the reception and transduction of incoming stimuli.
* various transmembrane channel proteins and enzymes are located at the surfaces of neurones where they are associated with ion transport
* the apparatus for protein synthesis (including RNA and ribosomes) occupies the soma and dendrites, but is usually absent from axons
* cytoplasm contains many mitochondria and moderate numbers of lysosomes. Golgi complexes are typically seen close to the nucleus, near the bases of the main dendrites and opposite the axon hillock.
* nucleus is characteristically large, round and euchromatic, with one or more prominent nucleoli, as is typical of all cells engaged in substantial levels of protein synthesis


Cytoskeleton:

* neuronal cytoskeleton is a prominent feature of its cytoplasm - gives shape, strength and rigidity to the dendrites and axons
* neurofilaments (the intermediate filaments of neurones) and microtubules are abundant
* they occur in the soma and extend along dendrites and axons - proportions vary with the type of neurone and cell process
* bundles of neurofilaments constitute neurofibrils which can be seen by light microscopy in silver stained sections
* neurofilaments are heteropolymers of proteins assembled from three polypeptide subunits, NF-L (68 kDa), NF-M (160 kDa) and NF-H (200 kDa)
* NF-M and NF-H have long C-terminal domains which project as side arms from the assembled neurofilament and bind to neighbouring filaments
* they can be heavily phosphorylated, particularly in the highly stable neurofilaments of mature axons, and are thought to give axons their tensile strength
* some axons are almost filled by neurofilaments


Microtubules:
* microtubules are important in axonal transport
* centrioles persist in mature postmitotic neurones, where they are concerned with the generation of microtubules rather than cell division
* centrioles are associated with cilia on the surfaces of developing neuroblasts
* their significance, other than at some sensory endings (e.g. the olfactory mucosa), is not known
* dendrites usually have more microtubules than axons


Pigmentation:

* pigment granules appear in certain regions, e.g. neurones of the substantia nigra contain neuromelanin, probably a waste product of catecholamine synthesis
* in the locus coeruleus a similar pigment, rich in copper, gives a bluish colour to the neurones
* some neurones are unusually rich in certain metals, which may form a component of enzyme systems, e.g. zinc in the hippocampus and iron in the oculomotor nucleus
* ageing neurones especially in spinal ganglia accumulate granules of lipofuscin (senility pigment)
* they represent residual bodies, which are lysosomes packed with partially degraded lipoprotein material (corpora amylaceae)


Dendrites:

* dendrites are highly branched, usually short processes which project from the soma
* branching patterns of many dendritic arrays are probably established by random adhesive interactions between dendritic growth cones and afferent axons which occur during development
* dendrites are overproduced in early development, then pruned in response to functional demand as the individual matures and information is processed through the dendritic tree
* there is evidence that dendritic trees may be plastic structures throughout adult life, expanding and contracting as the traffic of synaptic activity varies through afferent axodendritic contacts
* groups of neurones with similar functions have a similar stereotypic tree structure suggesting that the branching patterns of dendrites are important determinants of the integration of afferent inputs which converge on the tree
* dendrites differ from axons in many respects:
  • they represent the afferent rather than the efferent system of the neurone
  • receive both excitatory and inhibitory axodendritic contacts
  • may also make dendrodendritic and dendrosomatic connections, some of which are reciprocal
* synapses occur either on small projections called dendritic spines or on the smooth dendritic surface
* dendrites contain ribosomes, smooth endoplasmic reticulum, microtubules, neurofilaments, actin filaments and Golgi complexes
* the neurofilament proteins of dendrites are poorly phosphorylated
* dendrite microtubules express the microtubule-associated protein (MAP-2) almost exclusively in comparison with axons

* dendritic spine shapes range from simple protrusions to structures with a slender stalk and expanded distal end
* most spines are not more than 2 μm long, and have one or more terminal expansions, but they can also be short and stubby, branched or bulbous
* free ribosomes and polyribosomes are concentrated at the base of the spine
* ribosomal accumulations near synaptic sites provide a mechanism for activity-dependent synaptic plasticity through the local regulation of protein synthesis


AXONS

* axon originates either from the soma or from the proximal segment of a dendrite, at a specialized region, the axon hillock, which is free of Nissl granules
* action potentials are initiated here
* the axonal plasma membrane (axolemma) is undercoated at the hillock by a concentration of cytoskeletal molecules, including spectrin and actin fibrils, which are thought to be important in anchoring numerous voltage sensitive channels to the membrane
* the axon hillock is unmyelinated and often participates in inhibitory axo-axonal synapses
* this region of the axon is unique because it contains ribosomal aggregates immediately below the postsynaptic membrane


Myelin:

* when present, myelin begins at the distal end of the axon hillock
* myelin thickness and internodal segment lengths are positively correlated with axon diameter
* in the PNS unmyelinated axons are embedded in Schwann cell cytoplasm, in the CNS they lie free in the neuropil
* nodes of Ranvier are specialized constricted regions of myelin-free axolemma where action potentials are generated and where an axon may branch
* the density of sodium channels in the axolemma is highest at nodes of Ranvier, and very low along internodal membranes
* in contrast, sodium channels are spread more evenly within the axolemma of unmyelinated axons
* fast potassium channels are also present in the paranodal regions of myelinated axons.
* fine processes of glial cytoplasm (astrocyte in the CNS, Schwann cell in the PNS) surround the nodal axolemma
* the terminals of an axon are unmyelinated
* they expand into presynaptic boutons which may form connections with axons, dendrites, neuronal somata or, in the periphery, muscle fibres, glands and lymphoid tissue
* they may themselves be contacted by other axons, forming axoaxonal presynaptic inhibitory circuits. Further details of neuronal microcircuitry are given in Kandel & Schwartz (2000)


Axons:

* contain microtubules, neurofilaments, mitochondria, membrane vesicles, cisternae, and lysosomes: they do not usually contain ribosomes or Golgi complexes, except at the axon hillock
* however, ribosomes are found in the neurosecretory fibres of hypothalamo-hypophyseal neurones which contain the mRNA of neuropeptides
* organelles are differentially distributed along axons, e.g. there is a greater density of mitochondria and membrane vesicles in the axon hillock, at nodes, and in presynaptic endings
* axonal microtubules are interconnected by cross-linking microtubule-associated proteins (MAPs) of which tau is the most abundant
* microtubules have an intrinsic polarity: in axons all microtubules are uniformly orientated with their rapidly growing ends directed away from the soma towards the axon terminal
* neurofilament proteins ranging from high to low molecular weights are highly phosphorylated in mature axons, whereas growing and regenerating axons express a calmodulin-binding membrane-associated phosphoprotein, growth-associated protein-43 (GAP-43), as well as poorly phosphorylated neurofilament
* axons respond differently to injury, depending on whether the damage occurs in the CNS or PNS:
* the glial microenvironment of a damaged central axon does not facilitate regrowth, and reconnection with original synaptic targets does not normally occur
* in the PNS, the glial microenvironment is capable of facilitating axonal regrowth, however the functional outcome of clinical repair of a large mixed peripheral nerve, especially if the injury occurs some distance from the target organ, or produces a long defect in the damaged nerve, is frequently unsatisfactory


Axonal transport:

* neuronal organelles and cytoplasm are in continual motion
* bidirectional streaming of vesicles along axons results in a net transport of materials from the soma to the terminals, with more limited movement in the opposite direction
* two major types of transport occur, one slow, and one relatively fast:
* slow axonal transport is a bulk flow of axoplasm only in the anterograde direction, carrying cytoskeletal proteins and soluble, non-membrane bound proteins at a rate of c.0.1-3 mm a day
* in contrast, fast axonal transport carries vesicular material at c.200 mm a day in the retrograde direction and c.40 mm per day anterogradely
* rapid flow depends on microtubules
* vesicles with side projections line up along microtubules and are transported along them by their side-arms
* two microtubule-based motor proteins with ATPase activity are involved in fast transport: kinesin family proteins are responsible for the fast component of anterograde transport, and cytoplasmic dynein is responsible for retrograde transport
* fast anterograde transport carries vesicles, including synaptic vesicles containing neurotransmitters, from the soma to the axon terminals retrograde axonal transport accounts for the flow of mitochondria, endosomes and lysosomal autophagic vacuoles from the axonal terminals into the soma
* retrograde transport mediates the movement of neurotrophic viruses, e.g. herpes zoster, rabies and polio, from peripheral terminals, and their subsequent concentration in the neuronal soma


Synaptic transmission:

* transmission of impulses across specialized junctions (synapses) between two neurones is largely chemical
* depends on the release of neurotransmitters from the presynaptic side: this causes a change in the electrical state of the postsynaptic neuronal membrane, resulting in either its depolarization or hyperpolarization


Patterns of axonal termination vary considerably:

* a single axon may synapse with one neurone, e.g. climbing fibres ending on cerebellar Purkinje neurones, or more often with many, e.g. cerebellar parallel fibres, which provide an extreme example of this phenomenon
* in synaptic glomeruli, e.g. in the olfactory bulb, and synaptic cartridges, groups of synapses between two or many neurones form interactive units encapsulated by neuroglia


Electrical synapses (direct communication via gap junctions) are rare in the human CNS and are confined largely to groups of neurones with tightly coupled activity, e.g. the inspiratory centre in the medulla
__________________
Diane
www.dermoneuromodulation.com
SensibleSolutionsPhysiotherapy
HumanAntiGravitySuit blog
Neurotonics PT Teamblog
Canadian Physiotherapy Pain Science Division (Archived newsletters, paincasts)
Canadian Physiotherapy Association Pain Science Division Facebook page
@PainPhysiosCan
WCPT PhysiotherapyPainNetwork on Facebook
@WCPTPTPN
Neuroscience and Pain Science for Manual PTs Facebook page

@dfjpt
SomaSimple on Facebook
@somasimple

"Rene Descartes was very very smart, but as it turned out, he was wrong." ~Lorimer Moseley

“Comment is free, but the facts are sacred.” ~Charles Prestwich Scott, nephew of founder and editor (1872-1929) of The Guardian , in a 1921 Centenary editorial

“If you make people think they're thinking, they'll love you, but if you really make them think, they'll hate you." ~Don Marquis

"In times of change, learners inherit the earth, while the learned find themselves beautifully equipped to deal with a world that no longer exists" ~Roland Barth

"Doubt is not a pleasant mental state, but certainty is a ridiculous one."~Voltaire

Last edited by Diane; 26-04-2008 at 08:40 PM.
Diane is offline   Reply With Quote
Post New Thread  Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Microtubules Jon Newman Cells and Stars 9 29-11-2006 02:35 AM


All times are GMT +2. The time now is 04:06 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SomaSimple © 2004 - 2013