Vagus nerve

The main nerve of the body’s “rest and digest” calming system.

The vagus nerve is the longest cranial nerve and the backbone of your parasympathetic nervous system — the branch that slows your heart and calms you after a threat passes. A useful practical fact: your exhale gently stimulates it, which is why breathing out slowly, longer than you breathe in, is one of the fastest deliberate ways to lower your own arousal. Techniques like 4-7-8 breathing lean directly on this.