Midbrain

Anatomy

• It is located in Brainstem
• It is subdivided into three parts:
  • Tectum: It comprises superior and inferior colliculi and is the dorsal covering of the cerebral aqueduct.
    • Inferior colliculus receives input from several peripheral brainstem nuclei and auditory cortex
    • Superior colliculus is involved in the special sense of vision
  • Tegmentum
  • Ventral tegmental area (VTA) transmit axons of upper motor neurons.

Midbrain nuclei

• Periaqueductal gray which prevent pain sensation transmission.
• Oculomotor nerve nucleus (CN-3)
• Trochlear nerve nucleus (CN-4)
• Red nucleus: A motor nucleus that sends a descending tract to the lower motor neurons.
• Substantia nigra pars compacta: This is a concentration of neurons in the ventral portion of the midbrain that uses dopamine as its neurotransmitter and is involved in both motor function and emotion. Its dysfunction is implicated in Parkinson's disease.
• Reticular formation: Pain desensitization pathway, Arousal and consciousness systems, and contains the locus coeruleus, which is involved in intensive alertness modulation and in autonomic reflexes.
• Central tegmental tract: Directly anterior to the floor of the fourth ventricle, this is a pathway by which many tracts project up to the cortex and down to the spinal cord.
• VTA: A dopaminergic nucleus
• Rostromedial tegmental nucleus: A GABAergic nucleus

Related entities

• Diplopia (CN-3), (CN-4)
• UMN (Spasticity, Hyper reflexia) Red nucleus
• Parkinsonism (Tremor, Rigidity, Bradykinesia): Substantia nigra pars compacta
• Coma / Disorientation: Reticular formation
• Cranial nerve palsies
• Depression, Cognition (VTA)