What is it that makes the body get excited?
Adrenaline! A hormone produced by the body in « stressful » moments. These could be fear or extreme joy. Adrenal glands are responsible for producing adrenaline as & when the body requires it.
Situations most likely to cause a peak in adrenaline are group or solo adventures, parties, sports events, and in a more local context why not the pre-election meetings (^^,) ...
Adrenaline along with various other hormones puts the body in a state of readiness ahead of a situation. One usually feels excited before or during an event. It's the mind that pictures & creates the situation, thus alerting the rest of the body of what's happening next. The body responds by pumping adrenaline. The hormones altogether raise heart rate, increase respiration, dilate the pupils, slow down digestion and allow muscles to contract. Thus making the body more agile, allowing more information to be taken in & processed and helps the body use more energy.
Notice the text in bold? Adrenaline doesn't just act on the muscles but also allows the brain to process information easily. Maybe folks would now understand why I am most of the times in an « excited » stated during work (^^,) ...
Image source: raveshades.com