Vagus Physiology: Afferents, Efferents, Reflexes
Why 'stimulating the vagus' is never one single intervention.
What's covered
- 01Afferent signaling to NTS and onward to PBN, hypothalamus, insula
- 02Efferent parasympathetic outflow via DMNV and nucleus ambiguus
- 03Vagovagal reflexes: swallow, cough, gag, Hering-Breuer, Bezold-Jarisch
- 04Gastric motility, satiety, interoception
- 05Fiber types: A, B, C — recruitment thresholds
- 06Fascicular and somatotopic organization
What this means for you
Your vagus nerve is constantly sending signals up from your organs to your brain and back down — handling reflexes you don't think about, like swallowing, coughing, slowing your heart when you stand still too long, and telling your brain when your stomach is full.
Vagovagal reflex arcs underpin cough, gag, and Bezold-Jarisch–type cardioinhibitory responses. Important for syncope evaluation and stimulation planning. Recall: large myelinated A-fibers have lowest electrical threshold; small unmyelinated C-fibers (which carry much of the visceral afferent traffic) require higher current.
Organ- and function-specific fascicular organization (Settell et al., Brain Stim 2023+) is reshaping precision VNS device design. Selective stimulation of efferent vs afferent fibers, and of cardiac vs pulmonary vs immune-relevant pathways, is the frontier.
The vagus nerve only sends signals from brain to body.
About 80% of vagal fibers carry sensory information from organs to the brain; only ~20% are motor/efferent.