Brain stem mid brain (external & internal features)

🟣 3. The Midbrain (Mesencephalon)

🖇 Smallest part of the brainstem.

📌 External Features:

• Anterior surface: two large cerebral peduncles (crura cerebri); between them lies the interpeduncular fossa.
• Posterior surface (Tectum): has four colliculi (Corpora Quadrigemina):
• • Superior colliculi → visual reflexes
  • Inferior colliculi → auditory reflexes

📌 Cranial Nerves from the Midbrain:

• CN III (Oculomotor): emerges from the interpeduncular fossa (anterior).
• CN IV (Trochlear): the only cranial nerve emerging from the dorsal surface.

📌 Internal Structure (Transverse Section):

• Crus Cerebri: contains descending motor tracts.
• Substantia Nigra: dark-pigmented motor center.
• Tegmentum: contains the Red Nucleus and various ascending tracts.

🟠 4. Cranial Nerve Nuclei and Pathways

📌 Trigeminal Nuclei (CN V):

1. Main Sensory Nucleus → touch & pressure.
2. Spinal Nucleus → pain & temperature.
3. Mesencephalic Nucleus → proprioception.
4. Motor Nucleus → muscles of mastication.

📌 Facial Nucleus (CN VII):

• Motor fibers loop around CN VI nucleus, forming the Facial Colliculus on the floor of the 4th ventricle.

📌 Motor Nuclei Alignment:

• Aligned vertically in the brainstem: CN III, IV, VI, XII → control eye and tongue movements.

🟣 5. Functional Summary of Brainstem Components

🖇 Midbrain:

• Reflex centers for vision (superior colliculi) and hearing (inferior colliculi).
• Contains Red Nucleus and Substantia Nigra (motor control).

🖇 Pons:

• Relay center between cerebrum and cerebellum.
• Contains Pontine nuclei and tracts (vertical + transverse).

🖇 Medulla Oblongata:

• Forms lower part of brainstem.
• Contains vital centers for respiration, heart rate, and vasomotor control.

🚨 6. Key Exam-Focused Questions

الأسئلة دي لل Mid Brain وال Pons مع بعض

1. Which cranial nerve emerges from the dorsal surface?
   → CN IV (Trochlear).
2. What forms the floor of the 4th ventricle?
   → Posterior surfaces of the Pons and Medulla.
3. What separates the Pons and Medulla posteriorly?
   → Striae medullares (striae acusticae).
4. What are the two fiber directions in the Pons?
   → Transverse (Pontine) to cerebellum, Vertical (Corticopontine) from cortex.
5. Which Trigeminal nucleus handles pain & temperature?
   → Spinal nucleus of CN V.
6. Which motor nuclei are aligned for eye & tongue movement?
   → CN III, IV, VI, XII.
7. What are the functions of the four colliculi?
   → Superior → visual reflex; Inferior → auditory reflex.