Medúlla definition

(1) The inner part of an organ or structure in plant or animal

(2) 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"

(3) A white fatty substance that forms a medullary sheath around the axis cylinder of some nerve fibers