Brain stem medulla oblongata (external & internal features)

🧠 Brainstem & Medulla Oblongata Notes

🖇 General Structure of Brainstem

• 🟠 Consists of: Midbrain – Pons – Medulla Oblongata
• 🟣 Connects: Cerebral cortex (↑) ↔ Spinal cord (↓)
• 📌 Connected to Cerebellum via:
• • Midbrain → Superior Peduncles
  • Pons → Middle Peduncles
  • Medulla → Inferior Peduncles
• 📌 Ventricle: 4th ventricle (diamond shape) between Cerebellum (post) & Pons/Medulla (ant)
• Pons called "Abu Kirsh" (bulging belly appearance)

🖇 Functions of Brainstem

• 📌 Pathway: Ascending & descending tracts between brain & spinal cord
• 📌 Cranial nerves: Origin of CN III–XII (except I & II)
• 📌 Vital centers: Cardiovagal + Respiratory → essential for life (affected in hanging)
• 📌 Reticular Formation: Consciousness & arousal

🖇 Medulla Oblongata – External Features

🔸 Ventral (Anterior) Surface

• Anterior Median Fissure → divides medulla into halves
• Pyramids → corticospinal tract (motor)
• Decussation of Pyramids → 90% fibers cross → contralateral paralysis in lesions
• Olives → lateral to pyramids, over Inferior Olivary Nucleus
• Cranial Nerves:
• • CN XII → Pre-olivary sulcus (anterolateral)
  • CN IX, X, XI → Post-olivary sulcus (retro-olivary)

🔸 Dorsal (Posterior) Surface

• Divided into Closed Medulla (↓) & Open Medulla (↑, part of 4th ventricle)
• Closed Medulla:
• • Posterior Median Sulcus
  • Gracile tubercle (medial, Gracile nucleus)
  • Cuneate tubercle (lateral, Cuneate nucleus)
• Open Medulla:
• • Superior border → Striae Medullares
  • Floor of 4th ventricle:
  • • Hypoglossal Trigone (CN XII nucleus)
    • Vagal Trigone (CN X nucleus)

🖇 Key Questions (Exam Focus)

• 📌 Why CN III–XII only in Brainstem? → CN I & II are special sensory (not in brainstem)
• 📌 Which tract forms the Pyramids? → Corticospinal tract (motor to spinal cord)
• 📌 Clinical significance of Pyramidal Decussation? → Explains contralateral paralysis
• 📌 Which cranial nerve emerges dorsally? 🚨 CN IV (Trochlear) (unique exception)
• 📌 Why vital centers are important in hanging? → Their damage = death