That said, conversation between the CNS and ENS is constant. It begins the moment you sense food. In response to smells (or tastes, sights or the sounds of eating), your sensory organs send data to your brain (in the CNS). Your brain then sends information to your stomach, priming it for digestion.
Then while food passes through your gut, sensory nerve cells in its lining detect nutrient content. These cells send this information back to the brain (CNS), which might react—for example, by telling your system that you are full and should stop eating. “The CNS can ‘fine-tune’ the activity of the ENS,” Hyland says.
Meanwhile, these nerve cells in the gut also trigger reactions in the ENS. Specifically, they cause other cells and organs to secrete digestive enzymes to break down food and absorb nutrients, Anderson explains. For instance, they alert the gall bladder to secrete bile to break down fats, the stomach to release pepsin to break down proteins, and the pancreas to squirt out amylase to break down complex carbohydrates.
Although the CNS and ENS work in sync, they also operate independently. The CNS alone controls chewing and swallowing and the movement of food from the esophagus to the stomach. Meanwhile, the ENS controls digestive processes in the intestines and rectum exclusively.
Why does the ENS matter?