Figure 31.14: Where Does the Breathing Rhythm Originate? To find the neural tissue where the breathing rhythm starts, physiologists studied thin slices of living brain tissue from nestling mice. (A) This slice, cut from the medulla oblongata, has no connections to other parts of the nervous system. Its neural activity is therefore completely self-contained. (B) Electrical recordings were made from one of two clusters of nerve cells called the pre-Bötzinger complexes. The investigators found that these complexes generate electrical signals that control normal breathing. From simultaneous recordings from one of two other nerve cell clusters called the hypoglossal nuclei, the investigators found that the breathing rhythm that starts in the pre-Bötzinger complexes is relayed to the hypoglossal nuclei. In an intact mouse, the breathing rhythm would then be relayed to the breathing muscles via the hypoglossal nerves.