The mouth is the entry point for our nutrition. The most obvious function is to masticate, or chew, food to a size and texture able to pass through the esophagus to the stomach. Many more things happen in the mouth. Saliva contains enzymes that begin to break down food. The nerves of the brain send signals to the rest of the digestive tract to prepare for digestion. Both fluids and chewed foods have to be passed to the back of the throat and into the esophagus without blocking the breathing tube (the trachea).