Brain stem - pons (external & internal features)

🧠 Brainstem Anatomy and Associated Structures

🟣 1. General Development and Structure

🖇 Origin:
The brain develops from the neural tube, which closes at both ends.
The upper part expands into three primary vesicles:

1. Forebrain (Prosencephalon)
2. Midbrain (Mesencephalon)
3. Hindbrain (Rhombencephalon)

📌 Ventricles & Connections:

• The lateral ventricle is the largest.
• The Pons and Medulla form the floor of the 4th ventricle (rhomboid fossa).
• The Cerebellum connects to the brainstem via three peduncles — the middle cerebellar peduncle is the largest.

📌 Gray vs. White Matter:

• Gray matter → neuron cell bodies (nuclei inside the CNS).
• White matter → nerve fibers (axons).
• Cerebrum: gray outside, white inside.
• Brainstem & Spinal Cord: gray inside, white outside.

🟠 2. The Pons

🖇 Location:
Between the Midbrain (above) and Medulla Oblongata (below).

📌 External Features:

• Anterior surface: convex with a basilar sulcus (for basilar artery).
• Posterior surface: forms part of the 4th ventricle; separated from the medulla by striae medullares (striae acusticae).

📌 Internal Structure:
Divided into two parts:

1. Basilar portion (anterior):
2. • Contains Pontine nuclei (gray matter).
   • Two fiber directions:
   • • Transverse fibers (Pontine fibers) → connect to cerebellum via the middle peduncle.
     • Vertical fibers (Corticopontine fibers) → descend from cerebrum to Pontine nuclei.
2. Tegmentum (posterior):
3. • Contains ascending sensory tracts → Medial, Spinal, Lateral, and Trigeminal Lemnisci.

📌 Cranial Nerves from the Pons:

• CN V (Trigeminal): middle of the pons.
• CN VI (Abducens), CN VII (Facial), CN VIII (Vestibulocochlear): emerge at the ponto-medullary junction.

الأسئلة موجودة في محاضرة ال MIDBrain