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More than two vagus nerves
The two vagus nerves start in the brain at about the level of the ears, one on each side. They travel down the neck, across the chest, and into the abdomen, and along the way they send branches to organs that never cross your mind during the day, like the heart, the lungs, the pancreas, and the spleen.
The vagus nerve controls heart rate, the lungs, the diaphragm, and breathing rate. Each fiber carries instructions either from the body to the brain or from the brain to the body, and those instructions are critical to the healthy, balanced functioning of the organs and of health overall.
Why is it called the vagus nerve?
Vagus is Latin for wandering. Early anatomists chose the name because the nerve strays far from the head, down through the neck and chest to the abdomen. It is the tenth of twelve cranial nerves, which are the nerves that leave the brain directly rather than the spinal cord. It is also the longest of them.
Why do most vagus fibers carry signals upward?
Anatomical counts in animals show that roughly 80 percent of vagus fibers are afferent, which means they carry information from the organs to the brain. The brain relies on that stream to monitor the state of the heart, lungs, and gut. Many of those fibers report stretch, pressure, and chemistry in the tissues they pass through. The remaining fibers carry commands from the brain out to the organs.
Why do vagus fibers vary so much in thickness?
Fiber thickness and insulation set how fast a signal travels. Most vagal fibers are thin and unmyelinated, called C fibers, and they conduct at roughly one meter per second. Myelinated B fibers carry commands to organs like the heart at moderate speed. Large myelinated A fibers can conduct at up to about 100 meters per second.