Which of the following is NOT derived from the neural crest?

Explanation

## Neural Crest vs. Mesodermal Derivatives of the Eye ### Neural Crest Derivatives **Key Point:** Neural crest cells migrate extensively and give rise to diverse structures including melanocytes, odontoblasts, neurons, glia, and endocrine cells. Classic neural crest derivatives: - **Melanocytes** — pigment cells of skin, hair, eye - **Odontoblasts** — dentin-forming cells of teeth - **Adrenal medulla** — chromaffin cells (sympathetic neurons) - **Peripheral nervous system** — sensory and autonomic neurons, Schwann cells - **Cranial and spinal ganglia** - **Meninges** (pia and arachnoid) - **Connective tissue of head and neck** - **Iris stroma and corneal endothelium** ### Ocular Muscles: Mesodermal Origin **High-Yield:** The **extraocular muscles** (medial, lateral, superior, inferior recti; superior and inferior obliques) are derived from **paraxial mesoderm** (somites and prechordal mesoderm), NOT neural crest. The **ciliary muscle** is also **mesodermal** in origin — it is derived from the **mesoderm surrounding the optic cup**. The ciliary muscle is smooth muscle innervated by parasympathetic fibers (CN III) and functions to accommodate the lens. ### Ocular Structures: Origin Summary | Structure | Origin | | --- | --- | | Retina, optic nerve | Neuroectoderm (CNS) | | Lens, corneal epithelium | Surface ectoderm | | Sclera, choroid, corneal stroma | Mesoderm + neural crest | | Iris stroma | Neural crest | | **Ciliary muscle** | **Mesoderm** | | Extraocular muscles | Mesoderm | | Melanocytes (uvea, retina) | Neural crest | **Clinical Pearl:** When examining the eye, remember that the **smooth muscle components** (ciliary muscle, dilator/sphincter pupillae) have different origins — ciliary muscle is mesodermal, while the pupillary muscles are neural crest-derived smooth muscle. **Mnemonic: CONE** — Ciliary muscle is NOT neural crest; it's mesodermal (Ciliary = mOdal, Ocular muscles = mOdal, Neural crest = Elsewhere for eye).