( ( the ( parasympathetic system ) ) ( ( ( slows it ) down ) . ) )
(ROOT (S (NP (DT the) (JJ parasympathetic) (NN system)) (VP (VBZ slows) (NP (PRP it)) (PRT (RP down))) (. .)))
the parasympathetic system slows it down.
(ROOT (S (NP (DT The) (JJ parasympathetic) (NN system)) (VP (MD can) (ADVP (RB also)) (VP (VB be) (VP (VBN referred) (S (VP (TO to))) (PP (IN as) (NP (DT the) (JJ craniosacral) (NN system)))))) (. .)))