MeSH Tree Structures

Some terms appear in more than one branch of the tree. For example:

• Anatomy
  • Body Regions
    • Head
      • Ear

• Anatomy
  • Sense Organs
    • Ear
      • Ear, External +
      • Ear, Middle +
      • Ear, Inner +

The hierarchy allows a MEDLINE/PubMed search of a broader term to include the narrower terms in all branches automatically. This is known as "exploding." For example, a search of ear in PubMed would automatically explode to include records indexed with Ear, External; Ear, Middle; and Ear, Inner, as well as all narrower terms under each of these.