Medically known as ‘Enteric Nervous System’, our so-called second brain is a part of the Autonomic Nervous System. It consists of sheaths of 100 million neurons embedded in the walls of our digestive tract (alimentary canal) from the esophagus to the anus. It has its own reflexes and senses, and can behave independently of the brain for the process of digestion and excretion. The business of digestion is delegated to this nervous system in our gut. It controls the involuntary actions of the digestive system quite independently of any other components of nervous system.
That is precisely the reason why our psychological/emotional state drastically affects our gut and vice versa. This phenomenon is also known as the “Gut-Brain Axis.” It is well known that the stress and emotions originating from the brain can affect gastrointestinal function. Also, a sensation from the gastrointestinal tract can affect emotions and pain. For example, we get butterflies in our stomach when we are anxious, or when we have indigestion we may feel disturbed. We will see this in detail.
An inner layer of the gastrointestinal tract (esophagus, stomach, and intestines) is strongly muscular. But it is not under any voluntary control. These muscles break down food mechanically, mix it with digestive juices, and push it toward the other end. This process is called “Peristalsis” or “Peristaltic Reflex”.
Why is Enteric Nervous System considered Independent?
In medical science literature, the enteric nervous system is often classified as part of the parasympathetic nervous system. But, from a neuroscience perspective, though its actions appear to be largely parasympathetic and localized within the gastrointestinal tract, it gets the recognition of an independent third branch of the autonomic nervous system for the following reasons:
- The enteric nervous system is known to operate efficiently without any connection to any of the other nerves of the nervous system i.e. within the central nervous system (spinal cord) or within the parasympathetic nervous system (Vagus nerve – Cranial Nerve X). Even if all of the parasympathetic Vagus nerves from the brain to the intestine are severed in a person, the Peristalsis action remains active.
- It uses “Serotonin” as a neurotransmitter, which is active in the brain but is not found to be active in either the sympathetic or parasympathetic autonomic branches. The majority of Serotonin is actually produced in the gut!
- The enteric system also has its own sensors that do not connect with the central nervous systems or parasympathetic or sympathetic branches. Hence it is able to drive the peristaltic action independently.
- The enteric nervous system has over 100 million neurons – more neurons than in the spinal cord.
A link between Stress and Digestive functions
When the body is under stress – physical or emotional, the sympathetic nervous system (“stress response”) dominates. The blood is shunted towards the large muscles of the body for defense. And hence, the blood flow to the small intestine is severely curtailed. Consequently, peristalsis in the small intestine slows down. The transfer of nutrients from the small intestine into the intestinal vascular system comes to a halt. In the stomach, the acidity increases – leading to indigestion and heartburn.
If the stress is chronic, one craves complex carbohydrates (like pasta, bread), as these foods trigger the release of Serotonin in the brain – which is a calming neurotransmitter. When chronic stress is consistent, one can become addicted to the calming effects of serotonin release. This may result in an increase in body weight.
“Gut-Brain Axis” – A link between Emotions and Digestive functions
The gut-brain axis (GBA) consists of bidirectional signaling between the central and the enteric nervous system. It links the emotional and cognitive centers of the brain with digestive functions. For example, irritable bowel syndrome (IBS) is the most common phenomenon affected by the gut-brain axis. Many patients with IBS suffer from anxiety, and when their stress level increases, they tend to have more digestive problems like constipation, diarrhea, bloating.
The gut-brain axis includes the central nervous system, endocrine system, and immune systems. The particular components of interest among these systems include Hypothalamic-Pituitary-Adrenal (called HPA axis), the sympathetic nervous system, the parasympathetic nervous system, the enteric nervous system, and microbiota. Recent advances in neuroscience research have described the importance of gut microbiota in influencing these interactions. This interaction between microbiota and the gut-brain axis appears to be bidirectional i.e. signaling from gut-microbiota to brain and from the brain to gut-microbiota. This uses various neural, endocrine, immune channels.
“Ayurveda”, an ancient Indian medical science has been practiced for many thousands of years. The digestive system has long been an area of critical importance in the Ayurvedic system. Keeping the gut healthy to achieve overall wellness a key principle of Ayurveda. It is only now that modern science is acknowledging it as a key component in the regulation of physical and mental well-being.
The neuroscience research on the gut-brain axis is reasonably new. Over the past few years, scientific interest in the gut-brain axis has increased, mostly due to identification of the gut microbiota as a key player in this communication. The results of many neuroscience studies show that gut microbiota composition is influenced by emotional and physiological stress. Also, microbiota composition affects various nervous system activities such as stress response, behavior, and mood.
Scientific evidence is yet to be established on the influence of various Yogasanas in maintaining a healthy gut-brain axis. But it is very well known that Yogasanas that focus on the pelvic-abdominal region have a therapeutic effect on the mind – improving the mood, creating a positive attitude and bring emotional balance. Yogasana practice – restorative yoga poses in particular, are known to be effective in the reduction of stress and increase in the quality of life. Regular practice of Adhomukh Virasana, Adhomukh Swastikasana, Supta Baddha Konasana, Setubandha Sarvangasana, Viparit Karani, and Savasana is helpful in maintaining the health of the gut-brain axis.