What does chiefly animate Japanese soups and broths is an amino acid called glutamate. In the best ramen shops it's made naturally from boiling dried kombu seaweed; it can also come from dried shrimp or bonito flakes, or from fermented soy. More cheaply and easily, you get it from a tin, where it is stabilised with ordinary salt and is thus monosodium glutamate.
This last fact is of little interest to the Japanese - like most Asians, they have no fear of MSG. And there lies one of the world's great food scare conundrums. If MSG is bad for you - as Jeffrey Steingarten, the great American Vogue food writer once put it - why doesn't everyone in China have a headache?