Definition of "Medulla" :

noun: the inner part of an organ or structure in plant or animal

noun: lower or hindmost part of the brain; continuous with spinal cord; (bulb' is an old term for medulla oblongata)

"The medulla oblongata is the most vital part of the brain because it contains centers controlling breathing and heart functioning."

noun: a white fatty substance that forms a medullary sheath around the axis cylinder of some nerve fibers