At one time or another, we've all had the feeling of "butterflies" in our stomach before taking a test, or telling our crush we like them. This fluttery sensation makes us feel as if we're going to throw up, while our heart beats faster, our mouth is dry, and our palms are sweaty and shaky. This is a prime example of the brain-gut connection, a reaction to the psychological stress we’re experiencing in that moment.

Our gut instinct and the feeling of butterflies in our stomach are both signals coming from the second brain. Hidden within the walls of the digestive system, is the "brain in our gut," or enteric nervous system (ENS), according to Johns Hopkins Medicine. The ENS consists of two thin layers of more than 100 million nerve cells lining the gastrointestinal tract from the esophagus to the rectum. Its main role is controlling digestion, from swallowing to the release of enzymes that break down food, to controlling blood flow that helps with nutrient absorption and finally elimination. It communicates back and forth with the “big brain” to produce results.

The second brain communicates with our mind in several ways. A large portion of our emotions is believed to be influenced by the nerves in our gut. So, the butterflies in the stomach feeling is a signal in the gut that's part of our physiological fight-or-flight stress response. When we get nervous, signals travel from the thinking part of our brain to the hypothalamus and pituitary gland, which are responsible for controlling several bodily functions.

Then, the pituitary gland instantly signals the adrenal glands, which are on top of each kidney. The adrenal glands release adrenaline and other chemicals into your bloodstream. This is why we feel a more rapid heart rate, increased blood pressure and improved circulation in our muscles. As blood rushes to the lungs and muscles, it's pulled from other areas, such as the stomach, which results in the signature fluttery feeling.

Similar to the anxiety inspired by taking a test, love can trigger a spot in the brain, the medial insula, associated with perception of pain and gut feelings. In a study in NeuroReport, neurologists found the medial insula, which has a particular link with our gut, “lights up” when we see our crush or significant other. The physical effects of this brain activity can account for sensations we associate with love, like euphoria, butterflies in the stomach, love sickness, and love addiction.

Whether we’re nervous about taking a test or falling in love, trusting our “gut feeling” can help us understand the emotions triggered by certain situations a lot better.