The brain constitutes only about 2 percent of the human body, yet it is responsible for all of the body's functions. Learn about the parts of the human brain, as well as its unique defenses, like the blood brain barrier. ➡ Subscribe: http://bit.ly/NatGeoSubscribe About National Geographic: National Geographic is the world's premium destination for science, exploration, and adventure. Through their world-class scientists, photographers, journalists, and filmmakers, Nat Geo gets you closer to the stories that matter and past the edge of what's possible. Get More National Geographic: Official Site: http://bit.ly/NatGeoOfficialSite Facebook: http://bit.ly/FBNatGeo Twitter: http://bit.ly/NatGeoTwitter Instagram: http://bit.ly/NatGeoInsta Brain 101 | National Geographic https://www.youtube.com/watch?v=pRFXSjkpKWA National Geographic null