medulla

Noun

• the inner part of an organ or structure in plant or animal

• 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
    

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

Related words

• Synonyms: 
  medulla oblongata , bulb , myelin , myeline