 The general function of norepinephrine is to mobilize the brain and body for action . Norepinephrine release is lowest during sleep , rises during wakefulness , and reaches much higher levels during situations of stress or danger , in the so @-@ called fight @-@ or @-@ flight response . In the brain , norepinephrine increases arousal and alertness , promotes vigilance , enhances formation and retrieval of memory , and focuses attention ; it also increases restlessness and anxiety . In the rest of the body , norepinephrine increases heart rate and blood pressure , triggers the release of glucose from energy stores , increases blood flow to skeletal muscle , reduces blood flow to the gastrointestinal system , and inhibits voiding of the bladder and gastrointestinal motility . 
