Melissa has just completed running a marathon. She is so elated that she feels little fatigue or discomfort. Her lack of pain is probably the result of the release of

A) ACh.
B) endorphins.
C) dopamine.
D) norepinephrine.

Endorphins are natural neurotransmitters produced by the body that act as painkillers and can produce feelings of euphoria or well-being. They are released during exercise and can help mask feelings of fatigue and discomfort. This is likely why Melissa feels little pain or fatigue after running a marathon. ACh, dopamine, and norepinephrine do not play as significant a role in pain relief or euphoria as endorphins do.