Vagus Nerve is the largest cranial nerve in the body. It starts at the base of the skull and runs throughout the whole body. It plays a central role in your emotional and physical health. It directly influences the nervous system – particularly the Parasympathetic branch of the Autonomic Nervous System (covered in a previous post). Our breath, heart rate, and digestion — as well as our overall ability to experience the world (particular how to handle the stress in today’s world) — are all directly related to the Vagus Nerve.

In a normal course, when your mind perceives something dangerous or stressful, it activates the Sympathetic Nervous System (SNS i.e. fight-and-flight mode). This triggers a biological “Stress Response” to prepare the body to handle the situation. It causes lungs to furnish more oxygen to muscles, heart rate to increases to pump more blood, pupils of the eyes to dilate, various stress hormones to release, and much more.

For any reason, if this stress response stays activated for a longer period of time, without getting a chance for body and mind to calm down, it can cause various physical, physiological and emotional disorders. A consistently elevated stress response may create conditions like depression, anxiety, hypertension, diabetes. Hence it is important to get back to “Relaxation Response” as soon as the real danger is gone. This is nothing but activation of another branch of the autonomic nervous system called Parasympathetic Nervous System (PNS i.e. rest-and-digest mode),

When a relaxation response is activated, the Hypothalamus sends a signal through the vagus nerve to the heart to decrease the heart rate. At the same time, similar signals are sent to visceral organs to perform to their optimum level. For example, it triggers insulin production in the pancreas, acid production in the stomach and bile production in the liver.

There are two vagus nerves, the left and the right. Both go to the throat, lungs, heart, and upper stomach. The right vagus nerve continues into the abdominal cavity and connects with the digestive and reproductive organs all the way down to the perineum.

The vagus nerves pass through the chest cavity and hence the motions of the lungs and diaphragm seem to stimulate them. It is found that on inhalation, there is a sympathetic excitation of the heart – and the heart rate increases. On exhalation the parasympathetic response is activated through the vagus nerves – and hence the heart rate decreases. This alternating effect in the breathing cycle on the heart rate is known as the “Respiratory Sinus Arrhythmia (RSA)”.

There are two ways to voluntarily activate the parasympathetic mode:

• you convince your mind that you are safe so that it itself activates the relaxation response
• somehow the body signals the mind to stop the stress response. This is possible through the Vagus Nerve. In the Yogasana we use this method, which is nothing but a form of biofeedback (we covered in a post). Let’s see how.

The Vagus Nerve does the job of communicating relaxation response messages between the brain and the body. Anatomically the Vagus Nerve branches out to various parts of the body – mainly throat, lungs, heart, and abdominal organs. Out of these, you can voluntarily influence only throat and lungs (that means on your breath) – and that too only to a certain degree (without causing dangerous side effects). Such an influence can be activated through certain Yogasana postures or through certain Pranayama techniques that stimulate the Vagus Nerve.

Yogasana postures trigger the relaxation response through:

• deep and easy diaphragmatic breathing which naturally activates the Vagus Nerve and hence the parasympathetic nervous system. You can practice diaphragmatic breathing through certain Pranayama techniques. There are many Yogasana poses, particularly the restorative ones, that automatically induce diaphragmatic breathing without you consciously controlling the breath. We will cover them in detail in a future post.
• stimulating body-mind reflexes like Ocular-Vagal reflex and Baroreflex. We covered Ocular-Vagal reflex in an earlier post “Why should you cover eyes using a blanket or eye pillow during restorative yoga poses ”. We will soon cover “Baro-reflex”, which is stimulated in postures like Sarvangasana and Setubandha Sarvangasana.

The breath and body-mind reflexes directly influence your nervous system. This is the reason why it is always recommended that Yogasana and Pranayama practices be done only under the supervision of an experienced teacher.