vagus-nerve

Hiccups come from a three-part nerve reflex arc that fires the diaphragm early and snaps the vocal cords shut. Here is the mechanism, in detail.

In 1921, Otto Loewi transferred fluid from one frog heart to another and proved that nerves communicate chemically. The substance he found became acetylcholine.

The gut-brain axis explained: why nervousness, excitement, and love all produce the same fluttery stomach sensation through the vagus nerve and fight-or-flight.

Your gut and brain exchange signals through nerves, immune cells, and microbial chemicals. Here is what animal and human studies show about mood, anxiety, and cognition, and where the evidence is still thin.