A 30-year-old woman at 10 weeks gestation undergoes detailed embryological assessment. The clinician explains that the neural tube, which is currently closing, will eventually give rise to the entire central nervous system. Which of the following structures is NOT derived from the neural tube?

Explanation

## Neural Tube Derivatives The neural tube is the embryological precursor of the entire central nervous system (CNS). It arises from the ectoderm during the third week of gestation and undergoes primary neurulation to form the brain and spinal cord. ### Structures Derived from Neural Tube: - **Brain** (all three primary vesicles: prosencephalon, mesencephalon, rhombencephalon) - Cerebellum (from rhombencephalon/metencephalon) - Midbrain, pons, medulla - Cerebral hemispheres, thalamus, hypothalamus - **Spinal cord** - **Optic nerve** (CN II) — extends from the diencephalon as an outgrowth of the neural tube - **Olfactory nerve** (CN I) — from olfactory placode (though placode-derived, functionally CNS) ### Structures NOT Derived from Neural Tube: - **Peripheral sensory ganglia** (dorsal root ganglia, cranial nerve sensory ganglia) — derived from **neural crest**, not neural tube - Autonomic ganglia — neural crest origin - Schwann cells — neural crest origin - Melanocytes — neural crest origin **Key Point:** Neural crest cells migrate from the dorsal aspect of the closing neural tube and give rise to peripheral nervous system structures, including all sensory ganglia. This is a critical distinction in embryology. **High-Yield:** The neural tube gives rise to CNS; the neural crest gives rise to PNS ganglia and other non-neuronal structures.