I have had a look around the web, as well as here, and there seems to be a vagueness in the explanation of what causes butterflies in the stomach.
They say it’s brought on by a flow of adrenaline, during either good stress or bad, but they don’t go on to explain how that translates into the fluttery sensation itself.
What is actually going on in my gut when I’m nervous; what is it that manifests as butterflies? It feels physical, rather than mental, but is it? And if so, what’s jiggling about in there?
Really, you didn’t check Wikipedia? Release of adrenaline causes blood to be diverted to your muscles. Your stomach shuts down and you get the resulting tingly feeling.
This may be oblique or just wrong, but a while back I remember reading about a big net of nerves throughout the abdomen that appears to be a distant relative of the brain itself. IIRC the idea was that long ago the common ancestors of today’s typical animals had two clusters of nervous tissue, towards the ends. What became the brain, at the mouth end of the animal, clearly won over, and is generally thought of as the only one. But the other one is still hanging around as a faint echo of its former self. Supposedly it is most involved in emotional response. It’s the origin of concepts like “feel in in your gut”.
I realize that thinking doesn’t feel like it happens in a specific place, and overall the whole thing sound doubtful, but wherever I read it, I got the impression there was something to it.
That sounds like the enteric nervous system (ENS). It’s a massive largely self-contained neural network integrated into the gut that handles a lot of the local sensing and muscular activity. Not sure what the evolutionary background of it is, but it’s found throughout the intestines and is responsible for the various movements that the gut needs to do in order to move food from point A to point B. Denervation of the gut results in bad things happening (see Hirschprung’s disease, etc).