Swallowing, also known as deglutition, is the name for the process by which food goes from mouth to pharynx to esophagus. Swallowing has three phases - the oral, or buccal phase, the pharyngeal phase, and the esophageal phase. The oral phase is the only voluntary part of swallowing. After food has been chewed and moistened with saliva, the resulting bolus is pushed to the back of the throat, called the pharynx, by the tongue. This involves the tongue rolling back to prevent food from going forward into the mouth. As this happens, the soft palate rises to prevent food from entering the nasal cavity. The pharyngeal phase begins when receptors in the oropharynx are stimulated. This triggers initiation of the swallow reflex, which is involuntary. This part of swallowing must be coordinated perfectly, because the pharynx is the entrance to both the esophagus and the trachea. While the esophagus leads to the stomach, the trachea leads to the lungs. The vocal folds are located in the larynx, which is at the top of the trachea. The vocal cords close and the larynx gets pulled up as the epiglottis flips over the entrance to the trachea. The upper esophageal sphincter opens to allow the bolus to enter the esophagus. During the esophageal phase, food is propelled down the esophagus towards the stomach by waves of muscular contractions known as peristalsis. The larynx moves back down and the epiglottis flips back up so respiration can resume.