Aorta

noun

1. The great artery which carries the blood from the heart to all parts of the body except the lungs; the main trunk of the arterial system.
2. The liveliest part of something.

   "Tracing their battles, I had many occasions to walk along Second Avenue, the aorta of the Lower East Side, exploring places that were once as vibrant and tumultuous as Midtown Manhattan. http//travel.nytimes.com/2007/01/26/travel/escapes/26yiddish.html?8dpc"