Yoga and the Vagus Nerve

What is the vagus nerve?
The vagus nerve is a pair of cranial nerves which are extremely long, extending from the brain stem all the way to the internal organs.  It is also called “Cranial Nerve X”, as it is the 10th (of 12 paired) cranial nerve, or the “Wandering Nerve” (Vagus is Latin for “wandering”).
The vagus nerve emerges at the back of the skull and wanders through the abdomen, with a number of branching nerves coming into contact with the heart, lungs, voice box, stomach, and ears, etc. The vagus nerve carries incoming information from the nervous system to the brain, providing information about what the body is doing, and it also transmits outgoing information which governs a range of reflex responses.  Besides output to the various organs in the body, the vagus nerve conveys sensory information about the state of the body’s organs to the central nervous system.  80-90% of the nerve fibers in the vagus nerve are sensory nerves communicating the state of the organs to the brain.
The vagus nerve also helps to regulate the heartbeat, control muscle movement, keep a person breathing, and to transmit a variety of chemicals through the body. It is also responsible for keeping the digestive tract in working order, contracting the muscles of the stomach and intestines to help process food, and sending back information about what is being digested and what the body is getting out of it.
The vagus nerve supplies motor parasympathetic fibers to all the organs except the suprarenal (adrenal) glands, from the neck down to the second segment of the transverse colon. It also controls a few skeletal muscles.  This means that the vagus nerve is responsible for such varied tasks as heart rate, gastrointestinal peristalsis, sweating, and quite a few muscle movements in the mouth, including speech (via the recurrent laryngeal nerve) and keeping the larynx open for breathing (via action of the posterior cricoarytenoid muscle, the only abductor of the vocal folds). It also has some afferent fibers that innervate the inner (canal) portion of the outer ear, via the Auricular branch (also known as Alderman’s nerve) and part of the meninges. This explains why a person may cough when tickled on the ear.
When the vagus nerve is stimulated, the response is often a reduction in heart-rate or breathing. In some cases, excessive stimulation can cause someone to have what is known as a vaso-vagal response, appearing to fall into a faint or coma because his or her heart rate and blood pressure drop so much. Selective stimulation of this nerve is also used in some medical treatment; vagus stimulation appears to benefit people who suffer from depression, for example, and it is also sometimes used to treat epilepsy.
How is the vagus nerve related to Yoga?
The vagus nerve literally activates the parasympathetic nervous system – the body’s “rest and digest” system that functions when the body is not experiencing stress.  Doctors sometimes implant vagus nerve stimulators into patients with treatment-resistant depression, but yoga can produce this same effect.
How does Yoga stimulate the vagus nerve?
• Asana
When one practises asanas, one can activate the parasympathetic nervous system by massaging the organs, improving circulation, relaxing muscles, and quieting the mind.  For example, Sarvangasana.  Sarvangasana or Shoulder Stand, stimulates the vagus nerve most directly as it runs through the neck.  To maximize stimulation of the vagus nerve and protect it at the same time, practice the pose with the support of two or three folded yoga blankets. Stack the folded blankets evenly on top of each other and lie with your shoulder just at the edge of the blankets. In this way, when you move into the pose, the blankets will support your body weight. The neck, and the vagus nerve, will not be dangerously compressed and you will be able to experience the pose’s PNS activation. Gravity works to pull most of the blood in your body into the abdomen where it can nourish organs. This enhances your body’s ability to rest and digest.
• Pranayama
When we breathe deeply and slowly, we stimulate the vagus nerve resulting in activation of the  parasympathetic nervous system.  The PNS aims to turn off the brain and nervous system and helps to keep the systems relaxed and calm.  It promotes relaxation and rest by slowing our heart rate, slowing our breathing, constricts the pupils of our eyes, decreases muscular contraction and relaxes tissue throughout the body.
• Mantra
The vagus nerve controls physical functions in the throat, larynx, and ears – the area known as the throat chakra.  Chanting or listening to chants energizes nerves in the throat area via vibration and releases blocked energy.

Submitted by Lillian, 200 hour weekend Jul-Oct 2013
Eileen Pfefferle , Demand Media

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