Bragging about NeuroMOOC students
When I was first approached to teach a massively open on-line course or MOOC, I had never heard of the acronym and was only dimly aware in a vague way of Coursera and edX. Now, roughly 9 months later, I am finishing week 1 of my (really ours – doesn’t happen without an amazing team) very own MOOC: Understanding the Brain: The Neurobiology of Everyday Life, NeuroMOOC for short (@NeuroMOOC in Twitterese). The experience has been transformative. And the students are clearly enjoying the experience too! Not only are they enjoying it, they are incorporating what they learn into their experience of everyday life. For example, myelin has truly resonated with the students. The spouse of a former on-campus student is taking the course and my former student forwarded her spouse’s text message, “Super glad I have myelin because I almost fell while stretching. Whew for quick moving neural signals… Like, cheers for myelinated axons, amiright?!?” Two days into the course, Armando Duvoli found another use for myelin. He tweeted (@TrustInSciences) “Next time I’m upset I’ll just remember that at least my axons are Mylinated
@neuroMOOC #LovingThisClass”. Myelin being used for balance and for mental health – awesome!!
There is much fodder in this MOOC for many posts to come but for right now, I am going to stick to one big brag about the amazing, smart, clever students in Understanding the Brain. NeuroMOOC students are working and thinking and not settling for superficial information without understanding. The example that is the primary subject of this post started after I introduced the three layers of meninges (dura, arachnoid and pia) that surround the brain. I then explained how oligodendrocytes are glial cells that myelinate axons in the central nervous system and Schwann cells are the glia that myelinate axons in the peripheral nervous system.
Later, in a different segment, I went on to talk about tumors that should properly be called vestibular Schwannomas (because they are tumors made up of dividing Schwann cells) but are more typically called vestibular or auditory neuromas. I showed the students where vestibular Schwannomas form (at the root of cranial nerve VIII at the cerebellopontine angle). The students realized, without me explicitly saying it, that vestibular Schwannomas form inside the cranium and inside the dura! They then realized that something was awry given the information that I had communicated. They realized that the information given presented a paradox. Here is one students opening query:
“…is it not the oligodendrocytes that do the myelinating in the brain? (Schwann cells myelinate peripheral axons.)”
Right you are. Another student chimed in:
“Thanks for asking this, I had a similar thought, and wondered if these cancerous Schwann cells meant the nerves in question, though clearly within the brain (therefore part of the CNS) were in fact some sort of intrusion of the PNS?”
The latter student’s further comments are exemplary of how much the students are really working with the material:
“I had come to visualize the Meninges as a sort of diving suit or space suit for the PNS–the Dura mater as a kind of armor layer, then the arachnoid as an environmental seal and the pia mater as padding on the inside. Without thinking about it, I had embellished this model with the idea that nerves connecting the CNS to the PNS passed through some kind of ports in the meninges.”
My response was as follows: Dura as armor is a great analogy but pia is delicate and aimed at chemical rather than mechanical protection. So rather than viewing pia as padding, let’s think of pia as an environmental sealant, such as the polyurethane that is put on top of polished and stained wood. I couldn’t and still can’t think of a good analogy for arachnoid so we’ll leave that aside. The question then becomes, where is the edge of the brain? The answer is clear: it’s at the polyurethane, at the pia. The pia constitutes the blood brain barrier or BBB. Anything inside of the pia is brain/CNS and anything outside of the pia is PNS. Anything inside the dura of the skull is located in the cranium or intracranially.
Taking this concept further, we see that there are several areas that are inside the dura but outside the pia and still inside the cranium!! The pineal gland (see photo at top) is a good example.
The pineal attaches to the back of the midbrain, between the two superior colliculi. The pia gives out at the stalk. The pineal is not neuronal but rather a gland. It is one of a small number of tissues that is derived from neural tube but is not neural. Other examples include choroid epithelium (part of the choroid plexus) and the septum pellucidum.
To return to our original problem, the axons of cranial nerves (nerves that leave the skull rather than the spinal nerves which leave the vertebral column) exit the brain and leave the protective confines of the pia, while still well within the cranium and dural sac. As they exit the pia, these cranial nerve roots (the name for the nerves as they travel between the brain and the dura; spinal roots are the axonal bundles that travel between the spinal cord and the dura) get invested with Schwann cells. And yes, the same axons that are covered in Schwann cells outside of the pia are covered by oligodendrocytes inside of the pia.
Truthfully, this is fairly fancy neuroanatomy. A colleague of mine who is a neuropathologist was not aware that Schwann cells make myelin for the cranial nerve roots. So I thought to myself, “Great, the students are up to speed and all is well with the world”. As I was about to move on to another question, a student wrote:
” I am intrigued by how the pineal manages to be inside the dura and outside the pia. …Does this apply to the pituitary as well (ant. and post. or just anterior)?”
Well, that stumped me. So I dialed up a colleague who said he’d never thought of that and asked whether it was a question from a blog reader? When I told him that it was a question from a MOOC student, he was very surprised. But back to our story. After admitting that I did not know, and that my colleague did not know either, I gave my guess that both parts of the pituitary are outside dura and pia (probably wrong as it turns out). I added some more information:
As bundled axons (spinal or cranial) transition from central roots to peripheral nerves, dura is continuous with a tough membrane called epineurium which is the analog to dura in the PNS (you didn’t think we were going to leave those peripheral nerves completely vulnerable, did you??)…. Dura also extends out to cover the optic nerve and the back of the eye before it transitions into sclera which is in the front of the eye and which we see.
At this point the students and I were seriously down the rabbit hole. I thought, once again that we were done. But then Felipe Sales Nogueira Anorim Canedo posted this response:
“I was revisiting my neuroanatomy books to try to help solving this matter and I have come across this structure, the sellar diaphragm, that seems to be an infolding of the interior layer of the dura mater that covers the superior part of the hypophysis. That has left me with the impression that the dura would only cover the “roof” of the sella turcica, although, by saying only the most interior layer of the dura folds to form the diaphragm, the book may be implying that the inferior part of the sella is covered by the whole dura mater. I’m still not sure, but I’ve found this picture (cannot guarantee the reliabilty of the source) that seems to indicate that indeed the dura mater involves all of the pituitary – https://www.dartmouth.edu/~humananatomy/figures/chapter_43/43-22.HTM.
Regarding the pia mater involvement (no pun intended ^^), I’ve found no reference at all, so far, about its relation to the human hypophysis. However, I have found one article at PubMed about rats pituitaries that indicates only the neuro-hypophysis (posterior lobe of the gland) is covered by the pia mater, which I think is consistent with the fact that this part is almost an extension of the hypothalamus – http://www.ncbi.nlm.nih.gov/pubmed/7139318. And there are these three articles that imply the pituitary is either partially or not at all covered by the meninges, or even that the capsule it is surrounded by is originated from a primitive pia mater: a) http://www.ncbi.nlm.nih.gov/pubmed/23361322; b) http://www.ncbi.nlm.nih.gov/pubmed/7373394; c) http://www.ncbi.nlm.nih.gov/pubmed/845648.
I really don’t know what to think now but I look forward to your comments on that. I don’t know if I have helped at all, but I hope I’ve contributed a bit to the discussion.”
I don’t think that Felipe’s erudite contribution requires a word of commentary.
In closing, I will make a few points:
- First, Felipe is my teacher and I am his student. This is the ultimate dream for anyone interested in education. Talk about flipping the classroom!!
- Second, there are no flies on NeuroMOOCers. NeuroMOOCers are a smart, engaged, interesting and interested lot.
- Third, my colleagues in academia who underestimate the general public, do so at their own peril.
- Fourth, I have long had the hunch that the level of public discourse rises to the level that those in-the-know are willing to share and able to explain. These days leaders and experts talk down to the public. I don’t know whether that is because they are unable to explain themselves (suggesting they may not know what they are talking about) or because they think that the public is not smart or interested enough to understand. Regardless, NeuroMOOC is evidence to me that people will soak up information and think deeply if given the opportunity and the information.
I will end this post on a very serious note. To wit, what could be more fun than obsessing over the nervous system? MOOC on, NeuroMOOCers!