more on axon projections
Jyl Boline
I haven't come up with any consensus definitions for nerve, nerve
fiber bundle, tract and pathway, because it seems this discussion
isn't finished yet. Clif has pointed out that nerves are considered
part of the PNS, while tracts and pathways are considered part of the
CNS (although these are not synonymous).
However, Onard brought up an interesting suggestion, which I hoped
people might weigh in on before we move forward. While some of the
names are a little different than the ones we're discussing, perhaps
we can create synonyms and also use this this structure to help us
organize. I've pasted Onard's suggestion below and all comments and
suggestions would be greatly appreciated. Thanks much!
Neural fiber bundle (aggregate or collection of axons in cord-like
configuration)
- CNS fiber bundle -
( Here we need to resolve what is the difference or what
are the similarities between, TRACT, FASCICULUS, LEMNISCUS, STRIA,
ANSA, FUNICULUS, DECUSSATION, RADIATION and PATHWAY. Which ones are
subtypes of another and which one are parts of another? E.g.
corticospinal TRACT has a part " pyramidal DECUSSATION segment of
corticospinal tract". Are they defined based on structural or
functional properties or both?)
- PNS fiber bundle
- Nerve trunk
-Cranial nerve trunk
-Spinal nerve trunk
-Nerve root
-Nerve rootlet
-Nerve cord (e.g. lateral cord of brachial plexus)
Nerve in the FMA is a neural tree which consists of root, trunk and
branches (each branch consists of its own trunk and its own set of
branches).
Best,
Jyl
On Thu, Dec 16, 2010 at 2:56 PM, Mihail Bota <mbo...@gmail.com> wrote:
> Thank you for correction Dr. Saper.
>
> So, the criterion to dissociate a nerve from a tract is actually a
> structural one, not only a positional one - it is the type of the cell that
> produces myelin.
>
> Can I ask for references regarding the myelinization of cranial nerves? If
> we get this, then we can better answer the questions of Chris Mungall.
>
> Mihai
> On Thu, Dec 16, 2010 at 4:27 AM, <csa...@bidmc.harvard.edu> wrote:
>>
>> Mihail, the optic nerve is not a nerve. It is a misnomer, because it is a
>> CNS tract (it has central myelin). Nerves are PNS structures and have
>> peripheral myelin.
>>
>> As for the olfactory nerve, this is a misnomer as well, but of a different
>> kind, because there really is no olfactory nerve. There are olfactor nerve
>> rootlets, which run from the olfactory epithelium, through the cribiform
>> plate, into the olfactory bulb, but then never form a distinct nerve bundle.
>> The thing that most neuroanatomy teachers point to when they teach the
>> cranial nerves is actually the olfactory tract, from the olfactory bulb
>> (which is already part of the CNS) to the basal forebrain.
>>
>> Clif
>>
>>
>>
>>
>>
>> Clifford B. Saper, MD, PhD
>>
>> James Jackson Putnam Professor of Neurology and Neuroscience, Harvard
>> Medical School
>>
>> Chairman, Department of Neurology
>>
>> Beth Israel Deaconess Medical Center
>>
>> 330 Brookline Avenue, Boston, MA 02215 USA
>>
>> Phone: 617-667-2622; Fax: 617-975-5161
>>
>> Email: csa...@bidmc.harvard.edu
>>
>>
>>
>> Note: This message is confidential and may be legally privileged. It is
>> intended solely for the addressee. If you receive it in error, please delete
>> this message and notify the sender immediately. Any use by an unintended
>> recipient is prohibited.
>>
>> ________________________________
>>
>> From: Mihail Bota [mailto:mbo...@gmail.com]
>> Sent: Wednesday, December 15, 2010 8:52 PM
>> To: Chris Mungall
>> Cc: Jyl Boline; Maryann Martone; Saper,Clifford (Chief, BIDMC Neurology);
>> structura...@googlegroups.com;
>> pons-representati...@googlegroups.com;
>> neur...@googlegroups.com
>> Subject: Re: nucleus and ganglion
>>
>>
>>
>> Very good questions!
>> Please see below some of my answers.
>>
>> On Wed, Dec 15, 2010 at 5:25 PM, Chris Mungall <cjmu...@lbl.gov> wrote:
>>
>> No answers, only questions and some exercises to help improve these
>>
>> * can we list examples of each of these? E.g the cranial nerves.
>>
>> --the list:
>> http://brancusi.usc.edu/bkms/brain/ontology-details.php?id=852
>>
>> Also, FMC definition for nerves:
>>
>> http://brancusi1.usc.edu/thesaurus/definition/nerves/
>>
>> and for tracts
>>
>> http://brancusi1.usc.edu/thesaurus/definition/white-matter-tract/ -- this
>> one answers, at least partially, to some of your questions.
>>
>> See also the definitions of the vomeronasal nerve:
>> http://brancusi.usc.edu/bkms/brain/ontology-details.php?id=855
>>
>> of the optic nerve:
>>
>> http://brancusi.usc.edu/bkms/brain/ontology-details.php?id=859
>>
>> As you'll see, some subparts of them have "tract" in their names.
>>
>> Optic nerve and olfactory nerve are in CNS.
>>
>> I'll think at the remaining questions.
>>
>> Mihai
>>
>>
>> * what are the relationships between these classes? Is NFB a superclass of
>> both nerve and tract? If not, are they all mutually disjoint classes? I
>> presume not, but it's good to make all assumptions explicit
>>
>> * are tract and nerve disjoint classes? I presume so based on the CNS/PNS
>> distinction. Again, it's good to make this explicit
>>
>>
>>
>> * can we avoid weasel-words like "largely"? Is there a tract that does not
>> go from one CNS location to another? If so, mention it. If not, remove
>> "largely"
>>
>> * Are nerves always part_of the nervous system, or can they overlap with
>> the CNS? Is there a name for the structure that is a continuous nerve+tract?
>>
>> * Many AOs have a class "peripheral nerve" but treatment is inconsistent.
>> Can we come up with a good shared definition for this?
>>
>> * FMA divides things into neural tree organs and segments of neural tree
>> organs. For example, cranial nerve II is not a subclass of cranial nerve -
>> it's a subclass of nerve trunk, which is a subclass of segment of neural
>> tree organ. Do we want to adopt their definitions?
>>
>> On Dec 15, 2010, at 10:27 AM, Jyl Boline wrote:
>>
>> > Hello again All,
>> >
>> > So far we haven't had any feedback on our set of definitions having to
>> > do with nerves/tracts etc. This is what we have so far, but we're
>> > probably missing terms, and some of these may be synonyms. Please let
>> > me know your thoughts on these.
>> >
>> > Nerve:
>> > 1) Bundles of axons located in the peripheral nervous system
>> > 2) Segment of neural tree organ which has as its direct proper
>> > parts a nerve trunk and its branches; together with other nerves of
>> > the same tree it constitutes a neural tree.
>> >
>> > Nerve fiber bundle:
>> > A fasciculated bundle of neuron projections largely or completely
>> > lacking synapses.
>> >
>> > Tract:
>> > A collection of axons that largely arises from one central nervous
>> > system part and terminates in another. Tracts are generally named by
>> > their region or origin followed by their region of primary
>> > termination, e.g., mammillothalamic tract contains axons that arise
>> > from neurons in the mammillary bodies and terminate in the thalamus.
>> >
>> > Pathway:
>> > A collection of nerve fibers
>> >
>> > Thanks much!
>> >
>> > Best,
>> > Jyl
>> >
>>
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>>
>
Maryann Martone
textbooks etc suggest that tracts are distinguished by having a common
origin and common destination and are named accordingly, e.g.,
cortical spinal tract.
Lemniscus according to one definition is used to describe flattened
(i.e., "ribbon") macroscopic white matter associated with ascending
sensory systems.
Decussation is the crossing of fibers not connecting the same
structures on both sides of the brain, as opposed to a commissure
which connects the same structures on both sides. The decussation is
certainly a site, i.e., the place where fibers cross, but the
decussation also refers to the crossing fibers themselves.
Pathways need not be macroscopically visible nor represent a bundle of
axons, e.g., the perforant pathway.
I'm all for simplifying the current mess according to Onard's
suggestions. The idea is to make it computable. The preferred label
can reflect the historic name, e.g., fasciculus, lemniscus.
Maryann Martone
Professor-In-Residence
Dept of Neurosciences
University of California, San Diego
San Diego, CA 92093-0446
Tel: 858 822 0745
Fax: 858 246 0644
Jyl Boline
Does anyone have comments on this? Otherwise, in addition to the
definitions Maryann gave, these are the others I have:
Nerve:
Bundles of axons located in the peripheral nervous system
*Examples include the spinal nerves and cranial nerves III-XII
*Peripheral nerve is a synonym?
*(olfactory and optic nerves, are misnomers. Optic nerve is a CNS
tract, and Olfactory nerve is never really formed (instead, rootlets
give rise to the olfactory tract)
Nerve fiber bundle:
A fasciculated bundle of neuron projections in the PNS, largely or
completely lacking synapses.
*(considered a synonym of nerve?)
Tract:
Macroscopically visible collection of axons in the CNS that arise
principally from one CNS part and terminates in another CNS part.
Tracts are generally named by their region or origin followed by their
region of primary termination, e.g., mammillothalamic tract contains
axons that arise from neurons in the mammillary bodies and terminate
in the thalamus.
Pathway:
Not macroscopically visible collection of CNS nerve fibers from a
specific cell population of origin that travel together (although not
necessarily in a compact tract) to one or more specific targets.
Best,
Jyl
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Jyl Boline
replace "collection," any suggestions?
Nerve:
1) Bundles of neuron projects located in the peripheral nervous system
2) Segment of neural tree organ which has as its direct proper parts a
nerve trunk and its branches; together with other nerves of the same
tree it constitutes a neural tree.
Nerve fiber bundle:
A fasciculated bundle of neuron projections largely or completely
lacking synapses.
Tract:
A collection of neuron projections that largely arise from one central
nervous system part and terminates in another. Tracts are generally
named by their region or origin followed by their region of primary
termination, e.g., mammillothalamic tract contains axons that arise
from neurons in the mammillary bodies and terminate in the thalamus.
Pathway:
A collection of nerve fibers
Best,
Jyl
On Fri, Jan 28, 2011 at 11:55 AM, David Osumi-Sutherland
<dj...@gen.cam.ac.uk> wrote:
> On 28 Jan 2011, at 28/Jan/2011 16:50:45, Jyl Boline wrote:
>
>> Hello again All,
>>
>> Does anyone have comments on this? Otherwise, in addition to the
>> definitions Maryann gave, these are the others I have:
>>
>> Nerve:
>> Bundles of axons located in the peripheral nervous system
>> *Examples include the spinal nerves and cranial nerves III-XII
>> *Peripheral nerve is a synonym?
>> *(olfactory and optic nerves, are misnomers. Optic nerve is a CNS
>> tract, and Olfactory nerve is never really formed (instead, rootlets
>> give rise to the olfactory tract)
>>
>> Nerve fiber bundle:
>> A fasciculated bundle of neuron projections in the PNS, largely or
>> completely lacking synapses.
>> *(considered a synonym of nerve?)
>>
>> Tract:
>> Macroscopically visible collection of axons in the CNS that arise
>> principally from one CNS part and terminates in another CNS part.
>> Tracts are generally named by their region or origin followed by their
>> region of primary termination, e.g., mammillothalamic tract contains
>> axons that arise from neurons in the mammillary bodies and terminate
>> in the thalamus.
>
> I'd rather this was neutral about the type of projection. So, I'd rather say 'neuron projection' than axon here. Shouldn't we also be refering to fasciculated bundles here? Collection seems terribly vague.
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>
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>
Mihail Bota
1. neurite may mean axon + dendrite, but you may find situations when neurite means only axons.
2. a branch of a nerve can be named a nerve by itself. you say that a nerve should have a branching pattern; thus any n'th branch that tappens to branch for the (n+1)th time should be a nerve. thus, you'll have an explosion of nerves. or, if you allow "can", then you need an extra criterion to avoid inconsistencies. moreover, the branch that becomes nerve is automatically a trunk. So, a trunk will be made by other trunks, that are also branches...
One of the best cases to work over is the trigeminal nerve, I think. If we can solve we may be closer to a good working definition.
3. in this definition I do not see anywhere the dissociation between motor and sensory fibers. Without these, the nerve is "floating". The same is true for "tracts".
4. I'm still not convinced that "the tree organ" is the best approach. This "tree" maybe ensures a strict and rigid hierarchy in the computer system, but then, one of the counter-arguments is that the circulatory system may be viewed as a tree. However, this view is false, since the angles of the branches are not chaotic, but follow rules from liquid dynamics. How about the branches of a nerve?
Again, the "tree view" is just a view. And since it's so high in hierarchy for FMA, then it should have some very strong arguments for it.
Mihai
Hi all,
Creating definitions is a very difficult task especially if there is no theory behind it. Definitions can be general or created for a specific purpose but the goal is to provide enough understanding or information to get the message across or to serve a particular level of application. Definition (1) for nerve below is probably sufficient enough for you and me because we have implicit understanding of what we are talking about however for computability the definition does not disambiguate between a trunk, a branch, and an entire tree. Sometimes we must think out of the box or else we come up with useless definitions or definitions with limited use.
Before we talk about the nerve, the neural tree organ, the PNS and CNS, we have to explicitly represent first the structural substrates that comprise them. There is no question about axons and dendrites as neurites. What we need to define initially is the nerve fiber. This is an exercise and one which I use in the FMA.
- Nerve fiber consists of a neurite (or specifically an axon), a connective tissue sheath (endoneurium), vasculature of neurite, (and myelin sheath if myelinated: myelinated nerve fiber [has sibling class unmyelinated nerve fiber).
Nerve fiber
Myelinated nerve fiber
Unmyelinated nerve fiber
- Part of a nerve fiber has a CNS location, central part of nerve fibers (central nerve fiber), and a part in PNS, peripheral part of nerve fiber (peripheral nerve fiber).
In the FMA I will define 'Nerve fiber' as a heterogeneous anatomical cluster which consists of neurite, endoneurium, vasculature of neurite and has regional parts, central part of nerve fiber and peripheral part of nerve fiber. Outside the FMA (without being burdened by unwanted superclasses such as 'anatomical cluster'), one can perhaps define it as "a neural structure which consists of neurite, etc.", with 'neural structure' defined as a "primitive".
Peripheral nerve fiber is a segment of nerve fiber located outside the CNS (neuraxis).
Central nerve fiber is a segment of nerve fiber located inside the CNS (neuraxis).
Now we group them into a bundle, 'nerve fiber bundle', which has parts, 'central nerve fiber bundle' and 'peripheral nerve fiber bundle'. Nerve fiber bundle is an aggregate of nerve fibers arranged in a cord-like shape and has regional parts 'central nerve fiber bundle' and 'peripheral nerve fiber bundle'.
We can then define a bigger structure in terms of the constituents:
Nerve (synonym 'peripheral nerve') is an aggregate of peripheral nerve fiber bundles arranged in a branching pattern. Examples: Maxillary nerve, Nasopalatine nerve ( note that nasopalatine nerve is a branch of maxillary nerve but both satisfies the definition of "nerve". If required and necessary to distinguish between the two, additional properties can be implemented to represent primary, secondary and nAry branches).
Neural tree organ is a nonparenchymatous organ (or neural structure, see reason above) which consists of an aggregate of central nerve fiber bundles (central part of neural tree organ) continuous with a peripheral nerve (whole nerve).
Cranial nerve is a neural tree organ the central region of which is located in the brain.
Spinal nerve is a neural tree organ the central region of which is located in the spinal cord.
These definitions may require some refinements (structurally) and enhancements (physiologically, chemically, etc) but you can appreciate there is some structure or theory behind the representation.
best,
Onard
On Wed, 23 Feb 2011, Chris Mungall wrote:
On Feb 23, 2011, at 12:33 PM, Jyl Boline wrote:
OK, modifications are below, although I wasn't sure what to use to
replace "collection," any suggestions?
Nerve:
1) Bundles of neuron projects located in the peripheral nervous system
2) Segment of neural tree organ which has as its direct proper parts a
nerve trunk and its branches; together with other nerves of the same
tree it constitutes a neural tree.
For the purposes of evaluation I recommend expanding out recursive definitions. For (1) we can assume definitions for neuron projections and PNS, so nothing needs done here.
Here is an example for (2). I expanded out using FMA, assuming that is the source of the original definition:
Segment of neural tree organ which has as its direct proper parts a
nerve trunk and its branches; together with other nerves of the same
tree it constitutes a neural tree.
A neural tree organ is a nonparenchymatous organ which has as its parts an aggregate of neurons (nuclei or ganglia) and their axons which are grouped into fasciculi by connective tissue to form elongated, cable-like structures that are arranged into a tree.
A nerve trunk is a segment of neural tree organ which consists of nerve fiber bundles aggregated to form a cable-like structure that branches off to different nerves; together with all nerves of the same tree constitutes a neural tree
Onard would be able to do a better job here. A diagram might help. There's an almost circularity here, in that expanding the definitions for nerve itself leads to a reference to nerves. Also, this definition depends on a definition of "branches" which I can't find.