Mesencephalon

**Semantic type:** Body Part, Organ, or Organ Component

**Definition:** The uppermost portion of the brainstem located between the pons and the diencephalon. The midbrain contains the cerebral peduncles, oculomotor, trochlear and red nuclei, substantia nigra and various other nuclei and tracts.

**Synonyms:** - BRAIN, MIDBRAIN - MIDBRAIN - Mid-brain - Midbrain - Midbrain - midbrain