## Embryological Origin of Tissues The **peripheral nervous system (PNS)** is derived from the **ectoderm**, specifically from neural crest cells that arise from the neural tube. ### Germ Layer Derivatives: | Structure | Germ Layer Origin | |-----------|-------------------| | **Peripheral nervous system** | **Ectoderm (neural crest)** | | Central nervous system | Ectoderm (neuroectoderm) | | Epidermis, hair, nails | Ectoderm (surface ectoderm) | | Thyroid gland | Endoderm | | Liver | Endoderm | | Pancreas | Endoderm | | Skeletal muscle, bone, connective tissue | Mesoderm | ### Key Point: **Neural crest cells** are a specialized population of ectodermal cells that migrate extensively during embryonic development and give rise to: - Dorsal root ganglia - Sympathetic and parasympathetic ganglia - Schwann cells - Melanocytes - Adrenal medulla - Cranial nerve ganglia ### High-Yield Mnemonic: **"ENDO" for Endoderm** → **E**ndocrine glands (thyroid, pancreas), **N**otochord derivatives, **D**igestive tract, **O**ther organs (liver, lungs) The three endodermal derivatives in the options (thyroid, liver, pancreas) are all derived from the **foregut and midgut** endoderm, making them all incorrect.
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