( ( breathing center ) ( ( is ( in ( the ( medulla ( oblongata ( or ( brain stem ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN breathing) (NN center)) (VP (VBZ is) (PP (IN in) (NP (DT the) (NN medulla) (NN oblongata) (CC or) (NN brain) (NN stem)))) (. .)))
breathing center is in the medulla oblongata or brain stem.
(ROOT (S (NP (DT The) (NN brain) (NN stem)) (VP (VBZ regulates) (NP (NP (DT the) (NN rate)) (PP (IN of) (NP (NN breathing))))) (. .)))