The sympathetic nervous system is what gets the body ready to react, and is primarily activated by a release of norepinephrine. This handles the physiological changes. After that the parasympathetic nervous system is activated to handle the aftereffects.

Seriously, there's a great write-up on Wikipedia that handles everything from the physical to the cognitive effects. No research needed, it's all been done for you.

Amazing what a 5-second google search can give you.