Brainstem Anatomy (NEET PG Focus)
Brainstem anatomy is high-yield for the localization of lesions. Focus on the vertical columns of nuclei and the specific pathways passing through each level.
1. Midbrain (Tectum to Crus Cerebri)
- Level of Superior Colliculus: Contains CN III nucleus, Red Nucleus, and Substantia Nigra. Key pathway: Corticospinal tract in the middle 3/5 of the crus cerebri.
- Level of Inferior Colliculus: Contains CN IV nucleus (decussates dorsally).
2. Pons (Basal vs. Tegmentum)
| Level | Key Structures |
|---|---|
| Caudal Pons | CN VI and VII nuclei (Facial colliculus). |
| Mid Pons | Principal sensory and motor nuclei of CN V. |
3. Medulla (Open vs. Closed)
- Open (Upper Medulla): CN IX, X, XII nuclei; Nucleus Solitarius.
- Closed (Lower Medulla): Sensory decussation (medial lemniscus) and motor decussation (pyramidal).
NEET PG Hint: Remember the rule of 4s: 4 nerves in medulla (9-12), 4 in pons (5-8), 4 in midbrain (3-4). For lesions, medial structures start with ‘M’ (Motor pathway, Medial lemniscus, Medial longitudinal fasciculus, Motor nuclei 3, 4, 6, 12) and lateral structures start with ‘S’ (Spinothalamic, Sympathetic pathway, Spinocerebellar, Sensory nucleus of 5).