Ans. B. Pre botzinger complexRhythmic respiration is initiated by a small group of synaptically coupled pacemaker cells in the pre-Botzinger complex (pre-BOTC) on either side of the medulla between the nucleus ambiguus and the lateral reticular nucleus.The main components of the respiratory control pattern generator responsible for automatic respiration are located in the medulla.Rhythmic respiration is initiated by a small group of synaptically coupled pacemaker cells in the pre-Botzinger complex (pre-BOTC) on either side of the medulla between the nucleus ambiguus and the lateral reticular nucleus.