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The vagus nerve starts in the medulla, part of the brain stem, and it has dense upwards connections to the limbic system, the stress centers in the brain, made up of the amygdala, the hippocampus, the prefrontal cortex and the cingulate gyrus. When it leaves the skull and descends down through the neck into the trunk, it becomes the longest and most complex nerve in the body.19,20
The vagus motor fibers start in the nucleus ambiguous and control every muscle that controls speech and swallowing and even some muscles of the face. The recurrent laryngeal nerve opens the vocal cords so you can breathe, and a different branch closes the vocal cords so you can make sounds. The vagus nerve is why you can speak. The superior laryngeal branch of the vagus is why you can scream or sing high notes. The vagus supplies the pre-ganglionic neurons for the heart muscle. It beats your heart. The vagus moves your digestive system and vagus secretory fibers are why you have saliva and mucous in your pharynx and larynx. The vagus controls the smooth muscles in your bronchi and esophagus. The vagus is why you can swallow. The left side of the vagus slows the left ventricle (AV node) and it is why you do not have ventricular tachycardia. The right vagus slows the atria (sino-atrial, SA node) and it is why you don’t have atrial fibrillation.
The motor fibers of the vagus follow the esophagus through the diaphragm and it controls the esophageal sphincter that keeps the contents of the stomach out of your esophagus. The vagus is why you don’t have reflux.
When you’re under stress, your muscles and brain need glucose from the blood. The vagus has fibers to the liver that stop the liver from producing glucose. These vagus fibers need to be quiet when the stress response from the sympathetic nerves and the adrenal glands send signals to the liver to pump out more glucose so you can run.
The visceral sensory fibers of the vagus are why you know you have pain anyplace in your abdomen – the stomach, the liver, pancreas, spleen, and the gut. The vagus has stretch receptors in the stomach that tell you when you should stop eating. The vagus sensory fibers are why you feel hunger, satiety and nausea. The visceral pain information from your heart, esophagus, and trachea travel up the vagus and make you cough and tell you you’re having angina. The pressure receptors in the aortic arch and the airways tell your heart to slow down before something bursts. There are chemo receptors from the vagus in the aorta that tell your system that you need more bicarbonate from the pancreas. The vagus chemo receptors in the upper small intestine make you crave certain foods because you need certain nutrients. Those chemo receptors could also be responding to organic chemicals in the blood that cannot be processed by your liver because you lack the enzymes or substrate to take them apart. There aren’t good references for this hypothesis, but it’s a reasonable guess.
The recurrent branches of the vagus follow the posterior meningeal artery from the upper cervical spine into the skull. This branch is sensitive to dilation of the blood vessels in the posterior portion of the dura. This contributes to the sensation of headaches that happen when air pressure drops. Vagal nerve stimulators are approved for the treatment of migraine.
The vagus general sensory fibers carry sensations of touch, pain and temperature from the ear pharynx and larynx. The branch of the vagus for the ear (auricular branch) enters the superior vagal jugular ganglion and joins up with the C2-3 nerve root and the mandibular (lower) branch of cranial nerve V. The general sensory fibers from the pharynx and larynx join with the motor fibers.
This gets complicated but stay with it. It all makes sense and once you see it, you can’t ever un-see it.
All of the general sensory fibers of this portion of the vagus synapse within the spinal nucleus of Cranial Nerve V at the place where the cervical 3, 4 and 5 nerve roots exit the spine. Why is this important? In neurology you learn a memory trick, “C3-4-5 keep the diaphragm alive.” It’s why you cough when you put a cotton swab too far into your ear. It’s why you cough when you get something in your throat that you didn’t even know you swallowed. The sensory fibers of the vagus, join up with the motor fibers of the nerve roots that control your diaphragm and make you cough before you even know you need to. It’s automatic.19
Basically, the vagus nerve keeps you alive. It beats and controls your heart, moves your digestive system, keeps you from choking, allows you to empty your bowels and tells you what to eat and when you’re full, tells you that you have inflammation in your liver, pancreas or gut, regulates your blood sugar and allows you to breathe and speak.
And the vagus controls your immune system. This is where the vagus becomes crucial in FMS, CFS, and MCS. The vagus quiets the immune system by fibers that go from the celiac ganglion to the spleen to quiet T-cells and macrophages, and from the splenic nerve to the spleen to control antibody responses. Signals from the (afferent) vagus tell the brain when there is threat from infection, stress, or physical trauma. The brain sends signals down the vagus that tell the vagus to turn itself off or down. The (efferent) vagus by way of the celiac and splenic ganglia are now NOT turning off the macrophages, T-cells and antibodies in the spleen. If there is infection, stress, threat, or trauma, the vagus needs to be off to help with survival. The spleen and the immune system need to increase inflammation to fight infection and repair trauma.21
Take a moment and think about that. When life is good, the vagus slows the heart, digests your food, reduces inflammation, and quiets immune response. When there is threat, stress, infection or trauma you don’t need to digest your food, therefore you don’t need digestive enzymes or stomach acid or gut motility. You don’t need bronchial relaxation or a slow heart rate; you need stress hormones and the sympathetic nerves to dilate the bronchi and speed up your heart so you can run. You don’t need to sleep right now because you might miss your chance to run away if the threat eases for even a moment. You need to run away from the “tiger” that is chasing you.
When the vagus tells the brain that there is infection, threat, stress, or trauma, it sends those signals up from the body to the vagal nuclei in the medulla and that message goes directly up to the midbrain limbic system stress centers, the amygdala and the hippocampus, and others. The amygdala registers and mediates emotions and feelings. The hippocampus puts into subconscious, rarely conscious or sometimes conscious memory every “tiger” you’ve ever encountered. Every infection, every physical trauma, emotional trauma and every stress or threat is stored in the hippocampus so that the next time that threat is encountered, the hippocampus can remember how to get away from it faster. Short-term memory is reduced. There is only the “tiger.” Long-term memory is specific for every bad thing that has ever happened because the only thing you need to remember is how you got away from the “tiger” the last time. That’s why patients can only remember being sick since childhood. The threat receptors literally fire faster in the presence of very little objective external stimulus because the hippocampus remembers the last time this “tiger” was a threat.
And it doesn’t matter what the “tiger” is. The “tiger” response is primitive and exactly the same whether it is a stressful job, an abusive spouse, hunger and lack of nutrients, a broken leg, torn connective tissue because you have Ehlers Danlos syndrome and your connective tissue is constantly stretching past its integrity, or toxic chemical exposure, a virus, parasite, worm or dental or mold infection. If there is infection, stress or trauma, the vagus goes down or off, the immune system is unregulated, inflammation increases, and nothing works right.
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