Tectum and Tegmentum

brain midbrain mesencephalon tegmentum tectum

Brainstem and Midbrain

Midbrain Structures

• Periaqueductal Gray (PAG): around cerebral aqueduct; involved in pain modulation and defensive behaviors (e.g., freezing).
• Inferior colliculus: auditory processing and orienting.
• Red nucleus: motor control, connects cerebellum to spinal cord.
• Substantia nigra: dopamine, movement, reward, learning (degenerates in Parkinson’s).
• Ventral tegmental area (VTA): dopamine; reward, motivation, addiction.

Midbrain

• Divided into:
  • Tectum:
    • Superior colliculus – visual orienting, depth perception, blinking.
    • Inferior colliculus – auditory orienting response.
  • Tegmentum: contains reticular formation, raphe nuclei, and pathways for arousal and movement.