This is less about giving you physiological information- there’s nothing here you couldn’t look up yourself in six seconds- and more about demonstrating my process for fact checking information sources.
The Second Brain spends an awful lot of time talking about how miraculous the enteric nervous system (the nerves integrated with the large and small intestines) is (are), because they respond to stimuli in predictable manners even when cut off from the brain. It contrasts this with all other reflexes, with the implication that they do require a connection to the brain. That struck me as not right. I could have sworn the entire point of reflexes was that they worked without the brain.
I checked with Dr. Wikipedia, and I was half right. In humans reflexes are defined by not needing to reach the brain- but they do need to reach the spinal column. What makes the enteric system special is that it keeps operating without any connection to the spinal column or brain at all. That’s still not entirely unique; the heart does it too. But as it turns out, both the heart and intestines receive signals via my new fixation, the vagus nerve. The Second Brain talks as if the vagus nerve is the only connection the enteric system has with the gastrointestinal system, but like its use of the word reflex, I suspect I’m slightly misreading it. I’m very sure the heart has additional connections, because the vagus nerve is responsible for only the slow-down signal, and at a bare minimum there must be something to send a speed-up signal.