Have you ever experienced that nervous feeling of “butterflies” in your stomach? Or feel the toss and turn of your tummy just before boarding a roller coaster? Well, there may be more to it than just nerves that cause these feelings. Underlying these sensations is an extensive network of neurons lining our guts, which unfortunately is often over-looked. This system of neural tissue however, handles much more than digestion. In fact, a deeper understanding of this network of neurotransmitters has led many researchers to deem our guts as the “second brain”.
In connection with the brain in our heads, the “second brain” in our gut plays an important part in determining our mental state and is a major component of certain diseases throughout the body. The complicated system of the second brain consists of more than 100 million neurons, more than both the spinal cord and the peripheral nervous system. Known anatomically as the enteric nervous system, the second brain is composed of sheaths of neurons which are embedded in the walls of our intestines. Because the majority of the gut is focused on digestion (breaking down food, absorbing nutrients, and expelling waste), it is equipped with its own reflexes and senses – acting independently of the “first” brain.
Many scientists have been shocked to learn that 90 percent of the vessels in the vagus nerve (the primary visceral nerve of the brain) transport information from the gut to the brain, but not the other way around. That being said, the nerves in our gut could also influence a large majority of our emotions. Hence, the nervous “butterflies” in our stomach when we feel anxious.
More so, our everyday emotional well-being may be determined not only by our mind, but by our gut. Take for example, the treatment of depression. Just like the brain, the enteric nervous system (the gut), uses more than 30 neurotransmitters, and the bowels contain 95 percent of the body’s serotonin. Antidepressent medications, called selective serotonin reuptake inhibitors (SSRIs) increase serotonin levels in the brain and increase mood. However, these medications that are meant to cause chemical changes in the mind frequently incite gastrointestinal issues as a side effect.
Many researchers are employing cutting-edge technology to explore how the “second brain” mediates the body’s immune response; after all, 70 percent of the immune system is in the gut. Through this research, we are coming to learn that the serotonin produced by the “second brain” might also play a role in many other disorders from osteoporosis to autism.