GLOSSARY

The midbrain (mesencephalon) is the highest and smallest part of the brainstem, lying between the diencephalon and the pons, and plays a part in visual and auditory reflexes, eye movements, motor control (via the substantia nigra), reward, and arousal.

Important Structures

• Superior colliculi: visual reflexes, turning the eyes and head towards a sudden visual stimulus.
• Inferior colliculi: auditory relay, reacting to a sudden sound.
• Substantia nigra: produces dopamine for the basal ganglia; motor control.
• Ventral tegmental area (VTA): dopamine for reward and motivation.
• Red nucleus: motor coordination (especially of the arms).
• Nuclei of cranial nerves III and IV: eye movements and pupil constriction.
• Periaqueductal grey (PAG): descending pain inhibition.

Clinical Application