Examples would be epinephrine or adrenaline and norepinephrine. These are neurotransmitters of the sympathetic nervous system which is responsible for fight/flight response during situations that either threatens the host’s survival. Now, these neurotransmitters vasodilate the blood vessels increasing the flow of blood to many vital organs. Physiologically, increased heart rate, increased motor function and dilated pupils are some of the biological reactions to stressful situations.