( ( When ( ( a ( migraine headache ) ) ( is triggered ) ) ) ( , ( ( the ( trigeminal nerve ) ) ( ( ( ( releases neuropeptides ) , ) ( causing ( ( ( inflammation and ) dilation ) ( of ( the ( blood vessels ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT a) (JJ migraine) (NN headache)) (VP (VBZ is) (VP (VBN triggered))))) (, ,) (NP (DT the) (JJ trigeminal) (NN nerve)) (VP (VBZ releases) (NP (NNS neuropeptides)) (, ,) (S (VP (VBG causing) (NP (NP (NN inflammation) (CC and) (NN dilation)) (PP (IN of) (NP (DT the) (NN blood) (NNS vessels))))))) (. .)))
When a migraine headache is triggered, the trigeminal nerve releases neuropeptides, causing inflammation and dilation of the blood vessels.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (NN blood) (NNS vessels)) (PP (IN in) (NP (DT the) (NN head)))) (VP (VBP dilate)))) (, ,) (NP (NP (DT a) (NN migraine)) (, ,) (NP (DT a) (JJ severe) (NN headache)) (, ,)) (VP (MD can) (VP (VB occur))) (. .)))