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References: The Vagus Highway

  1. 13.4 The Peripheral Nervous System - OpenStax, Anatomy and Physiology 2e (CC BY 4.0) - Free open textbook section on the twelve cranial nerves, with a table showing which are sensory, motor, or mixed. A clear review of where the vagus nerve (CN X) fits in Section 2.3.

  2. 15.1 Divisions of the Autonomic Nervous System - OpenStax, Anatomy and Physiology 2e (CC BY 4.0) - Explains the sympathetic and parasympathetic branches, where their nerves leave the brainstem and spinal cord, and why "fight or flight" is an incomplete nickname.

  3. Internal senses of the vagus nerve - Prescott SL, Liberles SD. Neuron, 2022 - Research review on how vagal sensory neurons detect stretch, nutrients, and other signals from the organs. Source for the "about 80% sensory" figure (traced to classic animal fiber counts, a 1937 cat study by Foley and DuBois), the nodose ganglion to NTS pathway, and the 1% share of enteroendocrine cells.

  4. The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis - Bonaz B, Bazin T, Pellissier S. Frontiers in Neuroscience, 2018 - Open-access review describing the vagus as the main parasympathetic nerve, its 80/20 fiber split, how gut hormones signal through it, and the link between low vagal tone and IBD and IBS.

  5. A gut-brain neural circuit for nutrient sensory transduction - Kaelberer MM, et al. Science, 2018 - The mouse study that named neuropod cells, analyzed in this chapter's "How to read a gut-brain claim" box. The full text lists its experiments, funding, and patent disclosure.

  6. Extrinsic primary afferent signalling in the gut - Brookes SJ, Spencer NJ, Costa M, Zagorodnyuk VP. Nature Reviews Gastroenterology & Hepatology, 2013 - Review describing the three sensory pathways from the gut (vagal and two spinal) and the sensations they produce, such as fullness, nausea, urgency, and pain. The abstract is a good summary.

  7. Spinal Afferent Innervation of the Colon and Rectum - Brierley SM, Hibberd TJ, Spencer NJ. Frontiers in Cellular Neuroscience, 2018 - Open-access review of the spinal sensory nerves that reach the colon and rectum and how they give rise to discomfort, bloating, urgency, and pain. Background for Section 2.8.

  8. Vagal neurocircuitry and its influence on gastric motility - Travagli RA, Anselmi L. Nature Reviews Gastroenterology & Hepatology, 2016 - Explains the brainstem "vago-vagal" loop between the NTS and the dorsal motor nucleus and how it controls the stomach, including changes after stress. Advanced, but the opening sections are readable.

  9. Heart Rate Variability and Cardiac Vagal Tone in Psychophysiological Research - Laborde S, Mosley E, Thayer JF. Frontiers in Psychology, 2017 - Explains what HRV can and can't tell us about vagal tone and why HRV results are easy to misread. Useful for judging claims made by wearables and wellness apps.

  10. Function and mechanisms of enteroendocrine cells and gut hormones in metabolism - Gribble FM, Reimann F. Nature Reviews Endocrinology, 2019 - Review of how gut sensor cells release hormones such as GLP-1 in response to food, and how GLP-1-based medicines grew out of this research.

  11. A relic or still relevant: the narrowing role for vagotomy in the treatment of peptic ulcer disease - Lagoo J, Pappas TN, Perez A. American Journal of Surgery, 2014 - Surgical review explaining why vagotomy was once common for ulcers and why acid-reducing medicines and the discovery of H. pylori made it rare.

  12. Transcutaneous auricular vagus nerve stimulation attenuates inflammatory bowel disease in children: a proof-of-concept clinical trial - Sahn B, et al. Bioelectronic Medicine, 2023 - Small 16-week study of an ear stimulator in 22 young people aged 10 to 21 with IBD, cited in the At the Bedside case. Only the first 4 weeks had a sham comparison; the authors list their limits clearly.