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Vagus Signal Router

Run the Vagus Signal Router MicroSim Fullscreen

About This MicroSim

The vagus nerve is a two-way highway between the gut and the brainstem. Afferent fibers carry news up to the brain (stretch, nutrients, hormones, inflammation), and efferent fibers carry commands down to the gut. Classic fiber counts in animals suggest that about 80% of vagus fibers are afferent, so most of the traffic runs uphill.

This MicroSim shows a stylized body with the brain, the brainstem (with the nucleus tractus solitarius, NTS, where sensory signals arrive, and the dorsal motor nucleus, DMV, where motor signals leave), the nodose ganglion, the vagus nerve, and the gut. A second, separate path shows the spinal nerves, which carry many gut sensations, including much of gut pain, and the sympathetic (fight-or-flight) signals that slow digestion.

  • Teal pulses are afferent signals traveling up.
  • Coral pulses are efferent vagal signals traveling down; orange pulses on the spinal path are sympathetic signals.
  • The fiber bundle in the panel shows 8 of 10 fibers as sensory.
  • The Cut the vagus (vagotomy) checkbox blocks the vagus in both directions so you can see what still gets through.

How to Use

  1. Press Meal stretches stomach. Watch teal pulses rise to the NTS, then coral pulses leave the DMV and travel back down. This is the vago-vagal reflex that relaxes the upper stomach.
  2. Press Fat arrives (CCK). The gold sensor cell releases CCK, and afferent pulses carry a satiety signal up.
  3. Press Gut inflammation and notice that both the vagus and the spinal route light up.
  4. Press Stressful thought. This one starts in the brain: vagal output dips and sympathetic signals travel down the spinal route.
  5. Compare the Signals up and Signals down counters after several events.
  6. Check Cut the vagus (vagotomy) and repeat each event. Predict which signals still reach the brain before you press.
  7. Press Reset to clear the counters.

Learning Objective

Bloom level: Analyze. The learner will compare afferent (gut-to-brain) and efferent (brain-to-gut) vagus signaling across four everyday events, and contrast the vagal route with the spinal route.

Iframe Embed Code

<iframe src="https://aaryavvatts-lab.github.io/gut-brain-textbook/sims/ch02-vagus-signal-router/main.html" height="662px" width="100%" scrolling="no"></iframe>

Lesson Plan

Grade level: 9 to 12 (biology, anatomy and physiology, or health science)

Duration: 20 to 25 minutes

Activity:

  1. Warm-up (3 minutes). Ask: "When you feel full, which way is the signal traveling, from gut to brain or brain to gut?" Students write a prediction.
  2. Explore (8 minutes). In pairs, students trigger each event three times and record the Signals up and Signals down counters in a table.
  3. Compare (5 minutes). Students compare their up-to-down ratio with the 8-of-10 fiber bundle and explain why most vagus traffic is sensory.
  4. Predict and test (5 minutes). Before checking "Cut the vagus," each pair predicts which events will still reach the brain. Then they test it and connect the result to the vagotomy case in Chapter 2.
  5. Limits (3 minutes). Read the "What this model leaves out" box in the chapter and name one way the sim is simpler than a real nerve.

Assessment questions:

  1. What is the difference between an afferent and an efferent signal? Give one example of each from the sim.
  2. Why does the meal event send signals down only after signals arrive at the NTS?
  3. After the vagus is cut, which events can still reach the brain, and by what route?
  4. Why can't the sim's counters tell you the true percentage of sensory fibers in a human vagus nerve?

Chapter 2: The Vagus Highway