Neural Architecture 01: Reductionism in Illustrations of the Vagus and why this matters
AUTONOMIC PHYSIOLOGY
If you were to peruse the internet, or, for that matter, medical textbooks, looking for images of the Vagus nerve, you would come away with the impression that it is, as it sounds like from the name, a single nerve. When we learn about nerves in neurobiology, the template from which the conceptualization arises is based on the neuron, and the template of the neuron is a cell which has short dendrites to receive input signals, and a long axon. We tend to think of neurons as having long rope-like tails, and we tend to think of nerves in a similar manner: as telephone wires that connect distant parts of the body like so many telephone lines spanning the interstices between parts of us. The reality is so much more complex. Nerve cells come in such a radical proliferation of types that if you couldn't recognize their functional equivalence you wouldn't be able to class them together based on appearance, because they do not look anything alike, and many of them don't look much of anything like what we are taught a neuron looks like. This is important, because, similarly, the Vagus nerve looks nothing like a telephone wire. It looks more like a cloud of cotton candy woven through all the organs of the viscera. Let's deepen in.
This is the basic template of a neuron typically taught in collegiate and graduate school neurobiology courses.
This is a series of illustrations of different types of neurons in the human body.
Morphological variants in human neurons based on function.
One of the challenges of our (possibly?) necessarily reductionistic desire to simplify the systems of the human body so that we can understand them is that this abridging often denatures something fundamental about them, obscuring the multiple ways in which they actually work. If we think about the vagus as a 'wandering nerve', which is in fact the latinate origin of the name, we end up with a mental representation of it that is so far away from the neuro-anatomical reality as to actually obscure a direct experiential understanding of what the Vagus is, and what it is doing.
The illustration below is more or less how the Vagus is generally pictured diagrammatically. It is about the most accurate illustration you’ll find in the general world of these kinds of illustrations. It is accurate in as much as it correctly illustrates the sources of the vagus, it’s bi-laterality, and its innervation of visceral organs. 70% of vagal fibers are afferent, monitoring bodily processes, and we can see that the vagus touches the internal organs, so that is accurate enough. Yet it is also distortional in a way that largely precludes your understanding of how the Vagus actually works. In reality, the vagus is as different from this illustration as the Oak in winter, with no leaves, is from the Oak in summer, when most of what you see are leaves.
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