Behind the Brain

The vagus nerve is the one of the longest nerves of the human body. Made up of sensory and motor fibers, the vagus nerve interacts with the heart, lungs, and digestive system. Technically, the vagus nerves consist of two parts, the right and left vagal nerves, but they are referred to as one collective under the name vagus nerve.

Anatomy

The motor fibers of the vagus nerve originates from the medulla oblongata (the connection between the brainstem and the spinal cord). The sensory fibers come from the nodose ganglion. These fibers intertwine at the medulla oblongata, which is considered the origin of the vagal nerves. The vagus nerve then snakes down the jugular foramen (left and right), which is one of the opening at the base of the skull. From there, the vagus nerve continues into the carotid sheath, located between the internal carotid artery and the internal jugular vein. The vagus nerve goes all the way down to the neck, chest and abdomen.

Function

1. The vagus nerve is responsible for lowering heart rate. They do this by releasing acetychloline, which bonded to receptors on heart muscles, which slowed down heart rate. Thus stimulation of the vagus nerve results in slower heart rate.
2. The vagus nerve can also harm the heart, especially during emotional stress. Emotional stress causes unnecessary activation of the vagus nerve, which can result in a drop in cardiac output, or less blood being pumped out of the heart. This in extreme cases results in reflex syncope (passing out due to drop in blood pressure). Furthermore, vasovagal syncope can lead to loss of bladder control (peeing in pants) in young children.
3. The vagus nerve also affects the liver by leading to decreased production of glucose by the liver. When insulin is released, the vagus nerve decreases production of gluconeogenic enzymes which produce glucose.
4. Moving up the body, to the throat, the vagus nerve is responsible for the gag reflex. When the vagus nerve is touched, the soft palate elevates and moves toward the spot the vagus nerve was touched.
5. Another reflex the vagus nerve is responsible for is the inflammatory reflex. When a part of the body is injured/ inflamed, electrical signals are transmitted via the vagus nerve to prevent production of cytokine, which contributes to inflammation.
6. Speech is also controlled by the vagus nerve. The recurrent laryngeal nerve (RNL) is a branch of vagus nerve that give sensation to the larynx (AKA our voice box). Intrinsic muscles of the larynx, the posterior cricoarytenoid muscles are the only muscles that can open the vocal folds.
7. Digestion is also controlled by the vagus nerve. First of all, peristalsis (the movement of food down the esophagus) is affected by the vagus nerve. Secondly, the vagus nerve triggers the stomach to produce the correct amount of stomach acid, in order to properly digest food. Thirdly, in order for food to move to the intestines, it must pass through the pyloric valve, which opens by signaling of the vagus nerve. Lastly, once in the intestines, peristalsis must happen again to push food along the intestines. This peristalsis is also controlled by the vagus nerve.

Conclusion

Although we cannot see the vagus nerve, the wonders it does for our body are uncountable. From regulating our heart rate, to controlling our vocal folds, to regulating digestion, to controlling sweating and several reflexes, the vagus nerve provides several vital functions. It is one of the most important nerves in the whole nervous system, and it is truly fascinating how the vagus nerve interacts in different ways with different parts of our body.